Source/modules/webgl/WebGLRenderingContextBase.cpp

/*
 * Copyright (C) 2009 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "modules/webgl/WebGLRenderingContextBase.h"

#include "bindings/core/v8/ExceptionMessages.h"
#include "bindings/core/v8/ExceptionState.h"
#include "bindings/modules/v8/WebGLAny.h"
#include "core/dom/DOMArrayBuffer.h"
#include "core/dom/DOMTypedArray.h"
#include "core/dom/ExceptionCode.h"
#include "core/dom/FlexibleArrayBufferView.h"
#include "core/fetch/ImageResource.h"
#include "core/frame/LocalFrame.h"
#include "core/frame/Settings.h"
#include "core/html/HTMLCanvasElement.h"
#include "core/html/HTMLImageElement.h"
#include "core/html/HTMLVideoElement.h"
#include "core/html/ImageData.h"
#include "core/inspector/ConsoleMessage.h"
#include "core/inspector/InspectorInstrumentation.h"
#include "core/layout/LayoutBox.h"
#include "core/loader/FrameLoader.h"
#include "core/loader/FrameLoaderClient.h"
#include "modules/webgl/ANGLEInstancedArrays.h"
#include "modules/webgl/CHROMIUMSubscribeUniform.h"
#include "modules/webgl/CHROMIUMValuebuffer.h"
#include "modules/webgl/EXTBlendMinMax.h"
#include "modules/webgl/EXTFragDepth.h"
#include "modules/webgl/EXTShaderTextureLOD.h"
#include "modules/webgl/EXTTextureFilterAnisotropic.h"
#include "modules/webgl/OESElementIndexUint.h"
#include "modules/webgl/OESStandardDerivatives.h"
#include "modules/webgl/OESTextureFloat.h"
#include "modules/webgl/OESTextureFloatLinear.h"
#include "modules/webgl/OESTextureHalfFloat.h"
#include "modules/webgl/OESTextureHalfFloatLinear.h"
#include "modules/webgl/OESVertexArrayObject.h"
#include "modules/webgl/WebGLActiveInfo.h"
#include "modules/webgl/WebGLBuffer.h"
#include "modules/webgl/WebGLCompressedTextureASTC.h"
#include "modules/webgl/WebGLCompressedTextureATC.h"
#include "modules/webgl/WebGLCompressedTextureETC1.h"
#include "modules/webgl/WebGLCompressedTexturePVRTC.h"
#include "modules/webgl/WebGLCompressedTextureS3TC.h"
#include "modules/webgl/WebGLContextAttributeHelpers.h"
#include "modules/webgl/WebGLContextAttributes.h"
#include "modules/webgl/WebGLContextEvent.h"
#include "modules/webgl/WebGLContextGroup.h"
#include "modules/webgl/WebGLDebugRendererInfo.h"
#include "modules/webgl/WebGLDebugShaders.h"
#include "modules/webgl/WebGLDepthTexture.h"
#include "modules/webgl/WebGLDrawBuffers.h"
#include "modules/webgl/WebGLFramebuffer.h"
#include "modules/webgl/WebGLLoseContext.h"
#include "modules/webgl/WebGLProgram.h"
#include "modules/webgl/WebGLRenderbuffer.h"
#include "modules/webgl/WebGLShader.h"
#include "modules/webgl/WebGLShaderPrecisionFormat.h"
#include "modules/webgl/WebGLTexture.h"
#include "modules/webgl/WebGLUniformLocation.h"
#include "modules/webgl/WebGLVertexArrayObject.h"
#include "modules/webgl/WebGLVertexArrayObjectOES.h"
#include "platform/CheckedInt.h"
#include "platform/NotImplemented.h"
#include "platform/RuntimeEnabledFeatures.h"
#include "platform/geometry/IntSize.h"
#include "platform/graphics/GraphicsContext.h"
#include "platform/graphics/UnacceleratedImageBufferSurface.h"
#include "platform/graphics/gpu/AcceleratedImageBufferSurface.h"
#include "platform/graphics/gpu/DrawingBuffer.h"
#include "public/platform/Platform.h"
#include "wtf/ArrayBufferContents.h"
#include "wtf/PassOwnPtr.h"
#include "wtf/text/StringBuilder.h"

namespace blink {

namespace {

const double secondsBetweenRestoreAttempts = 1.0;
const int maxGLErrorsAllowedToConsole = 256;
const unsigned maxGLActiveContexts = 16;

} // namespace

// FIXME: Oilpan: static vectors to heap allocated WebGLRenderingContextBase objects
// are kept here. This relies on the WebGLRenderingContextBase finalization to
// explicitly retire themselves from these vectors, but it'd be preferable if
// the references were traced as per usual.
Vector<WebGLRenderingContextBase*>& WebGLRenderingContextBase::activeContexts()
{
    DEFINE_STATIC_LOCAL(Vector<WebGLRenderingContextBase*>, activeContexts, ());
    return activeContexts;
}

Vector<WebGLRenderingContextBase*>& WebGLRenderingContextBase::forciblyEvictedContexts()
{
    DEFINE_STATIC_LOCAL(Vector<WebGLRenderingContextBase*>, forciblyEvictedContexts, ());
    return forciblyEvictedContexts;
}

void WebGLRenderingContextBase::forciblyLoseOldestContext(const String& reason)
{
    size_t candidateID = oldestContextIndex();
    if (candidateID >= activeContexts().size())
        return;

    WebGLRenderingContextBase* candidate = activeContexts()[candidateID];

    // This context could belong to a dead page and the last JavaScript reference has already
    // been lost. Garbage collection might be triggered in the middle of this function, for
    // example, printWarningToConsole() causes an upcall to JavaScript.
    // Must make sure that the context is not deleted until the call stack unwinds.
    RefPtrWillBeRawPtr<WebGLRenderingContextBase> protect(candidate);

    candidate->printWarningToConsole(reason);
    InspectorInstrumentation::didFireWebGLWarning(candidate->canvas());

    // This will call deactivateContext once the context has actually been lost.
    candidate->forceLostContext(WebGLRenderingContextBase::SyntheticLostContext, WebGLRenderingContextBase::WhenAvailable);
}

size_t WebGLRenderingContextBase::oldestContextIndex()
{
    if (!activeContexts().size())
        return maxGLActiveContexts;

    WebGLRenderingContextBase* candidate = activeContexts().first();
    ASSERT(!candidate->isContextLost());
    size_t candidateID = 0;
    for (size_t ii = 1; ii < activeContexts().size(); ++ii) {
        WebGLRenderingContextBase* context = activeContexts()[ii];
        ASSERT(!context->isContextLost());
        if (context->webContext()->lastFlushID() < candidate->webContext()->lastFlushID()) {
            candidate = context;
            candidateID = ii;
        }
    }

    return candidateID;
}

void WebGLRenderingContextBase::activateContext(WebGLRenderingContextBase* context)
{
    unsigned removedContexts = 0;
    while (activeContexts().size() >= maxGLActiveContexts && removedContexts < maxGLActiveContexts) {
        forciblyLoseOldestContext("WARNING: Too many active WebGL contexts. Oldest context will be lost.");
        removedContexts++;
    }

    ASSERT(!context->isContextLost());
    if (!activeContexts().contains(context))
        activeContexts().append(context);
}

void WebGLRenderingContextBase::deactivateContext(WebGLRenderingContextBase* context)
{
    size_t position = activeContexts().find(context);
    if (position != WTF::kNotFound)
        activeContexts().remove(position);
}

void WebGLRenderingContextBase::addToEvictedList(WebGLRenderingContextBase* context)
{
    if (!forciblyEvictedContexts().contains(context))
        forciblyEvictedContexts().append(context);
}

void WebGLRenderingContextBase::removeFromEvictedList(WebGLRenderingContextBase* context)
{
    size_t position = forciblyEvictedContexts().find(context);
    if (position != WTF::kNotFound)
        forciblyEvictedContexts().remove(position);
}

void WebGLRenderingContextBase::willDestroyContext(WebGLRenderingContextBase* context)
{
    removeFromEvictedList(context);
    deactivateContext(context);

    // Try to re-enable the oldest inactive contexts.
    while(activeContexts().size() < maxGLActiveContexts && forciblyEvictedContexts().size()) {
        WebGLRenderingContextBase* evictedContext = forciblyEvictedContexts().first();
        if (!evictedContext->m_restoreAllowed) {
            forciblyEvictedContexts().remove(0);
            continue;
        }

        IntSize desiredSize = DrawingBuffer::adjustSize(evictedContext->clampedCanvasSize(), IntSize(), evictedContext->m_maxTextureSize);

        // If there's room in the pixel budget for this context, restore it.
        if (!desiredSize.isEmpty()) {
            forciblyEvictedContexts().remove(0);
            evictedContext->forceRestoreContext();
        }
        break;
    }
}

namespace {

GLint clamp(GLint value, GLint min, GLint max)
{
    if (value < min)
        value = min;
    if (value > max)
        value = max;
    return value;
}

// Return true if a character belongs to the ASCII subset as defined in
// GLSL ES 1.0 spec section 3.1.
bool validateCharacter(unsigned char c)
{
    // Printing characters are valid except " $ ` @ \ ' DEL.
    if (c >= 32 && c <= 126
        && c != '"' && c != '$' && c != '`' && c != '@' && c != '\\' && c != '\'')
        return true;
    // Horizontal tab, line feed, vertical tab, form feed, carriage return
    // are also valid.
    if (c >= 9 && c <= 13)
        return true;
    return false;
}

bool isPrefixReserved(const String& name)
{
    if (name.startsWith("gl_") || name.startsWith("webgl_") || name.startsWith("_webgl_"))
        return true;
    return false;
}

// Strips comments from shader text. This allows non-ASCII characters
// to be used in comments without potentially breaking OpenGL
// implementations not expecting characters outside the GLSL ES set.
class StripComments {
public:
    StripComments(const String& str)
        : m_parseState(BeginningOfLine)
        , m_sourceString(str)
        , m_length(str.length())
        , m_position(0)
    {
        parse();
    }

    String result()
    {
        return m_builder.toString();
    }

private:
    bool hasMoreCharacters() const
    {
        return (m_position < m_length);
    }

    void parse()
    {
        while (hasMoreCharacters()) {
            process(current());
            // process() might advance the position.
            if (hasMoreCharacters())
                advance();
        }
    }

    void process(UChar);

    bool peek(UChar& character) const
    {
        if (m_position + 1 >= m_length)
            return false;
        character = m_sourceString[m_position + 1];
        return true;
    }

    UChar current()
    {
        ASSERT_WITH_SECURITY_IMPLICATION(m_position < m_length);
        return m_sourceString[m_position];
    }

    void advance()
    {
        ++m_position;
    }

    static bool isNewline(UChar character)
    {
        // Don't attempt to canonicalize newline related characters.
        return (character == '\n' || character == '\r');
    }

    void emit(UChar character)
    {
        m_builder.append(character);
    }

    enum ParseState {
        // Have not seen an ASCII non-whitespace character yet on
        // this line. Possible that we might see a preprocessor
        // directive.
        BeginningOfLine,

        // Have seen at least one ASCII non-whitespace character
        // on this line.
        MiddleOfLine,

        // Handling a preprocessor directive. Passes through all
        // characters up to the end of the line. Disables comment
        // processing.
        InPreprocessorDirective,

        // Handling a single-line comment. The comment text is
        // replaced with a single space.
        InSingleLineComment,

        // Handling a multi-line comment. Newlines are passed
        // through to preserve line numbers.
        InMultiLineComment
    };

    ParseState m_parseState;
    String m_sourceString;
    unsigned m_length;
    unsigned m_position;
    StringBuilder m_builder;
};

void StripComments::process(UChar c)
{
    if (isNewline(c)) {
        // No matter what state we are in, pass through newlines
        // so we preserve line numbers.
        emit(c);

        if (m_parseState != InMultiLineComment)
            m_parseState = BeginningOfLine;

        return;
    }

    UChar temp = 0;
    switch (m_parseState) {
    case BeginningOfLine:
        if (WTF::isASCIISpace(c)) {
            emit(c);
            break;
        }

        if (c == '#') {
            m_parseState = InPreprocessorDirective;
            emit(c);
            break;
        }

        // Transition to normal state and re-handle character.
        m_parseState = MiddleOfLine;
        process(c);
        break;

    case MiddleOfLine:
        if (c == '/' && peek(temp)) {
            if (temp == '/') {
                m_parseState = InSingleLineComment;
                emit(' ');
                advance();
                break;
            }

            if (temp == '*') {
                m_parseState = InMultiLineComment;
                // Emit the comment start in case the user has
                // an unclosed comment and we want to later
                // signal an error.
                emit('/');
                emit('*');
                advance();
                break;
            }
        }

        emit(c);
        break;

    case InPreprocessorDirective:
        // No matter what the character is, just pass it
        // through. Do not parse comments in this state. This
        // might not be the right thing to do long term, but it
        // should handle the #error preprocessor directive.
        emit(c);
        break;

    case InSingleLineComment:
        // The newline code at the top of this function takes care
        // of resetting our state when we get out of the
        // single-line comment. Swallow all other characters.
        break;

    case InMultiLineComment:
        if (c == '*' && peek(temp) && temp == '/') {
            emit('*');
            emit('/');
            m_parseState = MiddleOfLine;
            advance();
            break;
        }

        // Swallow all other characters. Unclear whether we may
        // want or need to just emit a space per character to try
        // to preserve column numbers for debugging purposes.
        break;
    }
}

static bool shouldFailContextCreationForTesting = false;
} // namespace anonymous

class ScopedTexture2DRestorer {
    STACK_ALLOCATED();
public:
    explicit ScopedTexture2DRestorer(WebGLRenderingContextBase* context)
        : m_context(context)
    {
    }

    ~ScopedTexture2DRestorer()
    {
        m_context->restoreCurrentTexture2D();
    }

private:
    RawPtrWillBeMember<WebGLRenderingContextBase> m_context;
};

class ScopedFramebufferRestorer {
    STACK_ALLOCATED();
public:
    explicit ScopedFramebufferRestorer(WebGLRenderingContextBase* context)
        : m_context(context)
    {
    }

    ~ScopedFramebufferRestorer()
    {
        m_context->restoreCurrentFramebuffer();
    }

private:
    RawPtrWillBeMember<WebGLRenderingContextBase> m_context;
};

class WebGLRenderingContextLostCallback final : public GarbageCollectedFinalized<WebGLRenderingContextLostCallback>, public WebGraphicsContext3D::WebGraphicsContextLostCallback {
public:
    static WebGLRenderingContextLostCallback* create(WebGLRenderingContextBase* context)
    {
        return new WebGLRenderingContextLostCallback(context);
    }

    ~WebGLRenderingContextLostCallback() override { }

    virtual void onContextLost() { m_context->forceLostContext(WebGLRenderingContextBase::RealLostContext, WebGLRenderingContextBase::Auto); }

    DEFINE_INLINE_TRACE()
    {
        visitor->trace(m_context);
    }

private:
    explicit WebGLRenderingContextLostCallback(WebGLRenderingContextBase* context)
        : m_context(context) { }

    RawPtrWillBeMember<WebGLRenderingContextBase> m_context;
};

class WebGLRenderingContextErrorMessageCallback final : public GarbageCollectedFinalized<WebGLRenderingContextErrorMessageCallback>, public WebGraphicsContext3D::WebGraphicsErrorMessageCallback {
public:
    static WebGLRenderingContextErrorMessageCallback* create(WebGLRenderingContextBase* context)
    {
        return new WebGLRenderingContextErrorMessageCallback(context);
    }

    ~WebGLRenderingContextErrorMessageCallback() override { }

    virtual void onErrorMessage(const WebString& message, WGC3Dint)
    {
        if (m_context->m_synthesizedErrorsToConsole)
            m_context->printGLErrorToConsole(message);
        InspectorInstrumentation::didFireWebGLErrorOrWarning(m_context->canvas(), message);
    }

    DEFINE_INLINE_TRACE()
    {
        visitor->trace(m_context);
    }

private:
    explicit WebGLRenderingContextErrorMessageCallback(WebGLRenderingContextBase* context)
        : m_context(context) { }

    RawPtrWillBeMember<WebGLRenderingContextBase> m_context;
};

PassOwnPtr<WebGraphicsContext3D> WebGLRenderingContextBase::createWebGraphicsContext3D(HTMLCanvasElement* canvas, WebGLContextAttributes attributes, unsigned webGLVersion)
{
    Document& document = canvas->document();
    LocalFrame* frame = document.frame();
    if (!frame) {
        canvas->dispatchEvent(WebGLContextEvent::create(EventTypeNames::webglcontextcreationerror, false, true, "Web page was not allowed to create a WebGL context."));
        return nullptr;
    }
    Settings* settings = frame->settings();

    // The FrameLoaderClient might block creation of a new WebGL context despite the page settings; in
    // particular, if WebGL contexts were lost one or more times via the GL_ARB_robustness extension.
    if (!frame->loader().client()->allowWebGL(settings && settings->webGLEnabled())) {
        canvas->dispatchEvent(WebGLContextEvent::create(EventTypeNames::webglcontextcreationerror, false, true, "Web page was not allowed to create a WebGL context."));
        return nullptr;
    }

    WebGraphicsContext3D::Attributes wgc3dAttributes = toWebGraphicsContext3DAttributes(attributes, document.topDocument().url().string(), settings, webGLVersion);
    WebGLInfo glInfo;
    OwnPtr<WebGraphicsContext3D> context = adoptPtr(Platform::current()->createOffscreenGraphicsContext3D(wgc3dAttributes, 0, &glInfo));
    if (!context || shouldFailContextCreationForTesting) {
        shouldFailContextCreationForTesting = false;
        String statusMessage;
        if (!glInfo.contextInfoCollectionFailure.isEmpty()) {
            statusMessage.append("Could not create a WebGL context. ");
            statusMessage.append(glInfo.contextInfoCollectionFailure);
            String vendorId = String::number(glInfo.vendorId);
            String deviceId = String::number(glInfo.deviceId);
            if (vendorId.isEmpty())
                statusMessage.append("VendorId = Not Available");
            else
                statusMessage.append("VendorId = " + vendorId);
            if (deviceId.isEmpty())
                statusMessage.append(", DeviceId = Not Available");
            else
                statusMessage.append(", DeviceId = " + deviceId);
        } else {
            statusMessage.append("Could not create a WebGL context");
            if (!glInfo.vendorInfo.isEmpty()) {
                statusMessage.append(", VendorInfo = ");
                statusMessage.append(glInfo.vendorInfo);
            } else {
                statusMessage.append(", VendorInfo = Not Available");
            }
            if (!glInfo.rendererInfo.isEmpty()) {
                statusMessage.append(", RendererInfo = ");
                statusMessage.append(glInfo.rendererInfo);
            } else {
                statusMessage.append(", RendererInfo = Not Available");
            }
            if (!glInfo.driverVersion.isEmpty()) {
                statusMessage.append(", DriverInfo = ");
                statusMessage.append(glInfo.driverVersion);
            } else {
                statusMessage.append(", DriverInfo = Not Available");
            }
            statusMessage.append(".");
        }
        canvas->dispatchEvent(WebGLContextEvent::create(EventTypeNames::webglcontextcreationerror, false, true, statusMessage));
        return nullptr;
    }

    return context.release();
}

void WebGLRenderingContextBase::forceNextWebGLContextCreationToFail()
{
    shouldFailContextCreationForTesting = true;
}

namespace {

// ES2 enums
static const GLenum kSupportedInternalFormatsES2[] = {
    GL_RGB,
    GL_RGBA,
    GL_LUMINANCE_ALPHA,
    GL_LUMINANCE,
    GL_ALPHA,
};

// Exposed by GL_ANGLE_depth_texture
static const GLenum kSupportedInternalFormatsOESDepthTex[] = {
    GL_DEPTH_COMPONENT,
    GL_DEPTH_STENCIL,
};

// Exposed by GL_EXT_sRGB
static const GLenum kSupportedInternalFormatsEXTsRGB[] = {
    GL_SRGB,
    GL_SRGB_ALPHA_EXT,
};

// ES3 enums
static const GLenum kSupportedInternalFormatsES3[] = {
    GL_R8,
    GL_R8_SNORM,
    GL_R16F,
    GL_R32F,
    GL_R8UI,
    GL_R8I,
    GL_R16UI,
    GL_R16I,
    GL_R32UI,
    GL_R32I,
    GL_RG8,
    GL_RG8_SNORM,
    GL_RG16F,
    GL_RG32F,
    GL_RG8UI,
    GL_RG8I,
    GL_RG16UI,
    GL_RG16I,
    GL_RG32UI,
    GL_RG32I,
    GL_RGB8,
    GL_SRGB8,
    GL_RGB565,
    GL_RGB8_SNORM,
    GL_R11F_G11F_B10F,
    GL_RGB9_E5,
    GL_RGB16F,
    GL_RGB32F,
    GL_RGB8UI,
    GL_RGB8I,
    GL_RGB16UI,
    GL_RGB16I,
    GL_RGB32UI,
    GL_RGB32I,
    GL_RGBA8,
    GL_SRGB8_ALPHA8,
    GL_RGBA8_SNORM,
    GL_RGB5_A1,
    GL_RGBA4,
    GL_RGB10_A2,
    GL_RGBA16F,
    GL_RGBA32F,
    GL_RGBA8UI,
    GL_RGBA8I,
    GL_RGB10_A2UI,
    GL_RGBA16UI,
    GL_RGBA16I,
    GL_RGBA32I,
    GL_RGBA32UI,
    GL_DEPTH_COMPONENT16,
    GL_DEPTH_COMPONENT24,
    GL_DEPTH_COMPONENT32F,
    GL_DEPTH24_STENCIL8,
};

// ES2 enums
static const GLenum kSupportedFormatsES2[] = {
    GL_RGB,
    GL_RGBA,
    GL_LUMINANCE_ALPHA,
    GL_LUMINANCE,
    GL_ALPHA,
};

// Exposed by GL_ANGLE_depth_texture
static const GLenum kSupportedFormatsOESDepthTex[] = {
    GL_DEPTH_COMPONENT,
    GL_DEPTH_STENCIL,
};

// Exposed by GL_EXT_sRGB
static const GLenum kSupportedFormatsEXTsRGB[] = {
    GL_SRGB,
    GL_SRGB_ALPHA_EXT,
};

// ES3 enums
static const GLenum kSupportedFormatsES3[] = {
    GL_RED,
    GL_RED_INTEGER,
    GL_RG,
    GL_RG_INTEGER,
    GL_RGB,
    GL_RGB_INTEGER,
    GL_RGBA,
    GL_RGBA_INTEGER,
    GL_DEPTH_COMPONENT,
    GL_DEPTH_STENCIL,
};

// ES2 enums
static const GLenum kSupportedTypesES2[] = {
    GL_UNSIGNED_BYTE,
    GL_UNSIGNED_SHORT_5_6_5,
    GL_UNSIGNED_SHORT_4_4_4_4,
    GL_UNSIGNED_SHORT_5_5_5_1,
};

// Exposed by GL_OES_texture_float
static const GLenum kSupportedTypesOESTexFloat[] = {
    GL_FLOAT,
};

// Exposed by GL_OES_texture_half_float
static const GLenum kSupportedTypesOESTexHalfFloat[] = {
    GL_HALF_FLOAT_OES,
};

// Exposed by GL_ANGLE_depth_texture
static const GLenum kSupportedTypesOESDepthTex[] = {
    GL_UNSIGNED_SHORT,
    GL_UNSIGNED_INT,
    GL_UNSIGNED_INT_24_8,
};

// ES3 enums
static const GLenum kSupportedTypesES3[] = {
    GL_BYTE,
    GL_UNSIGNED_SHORT,
    GL_SHORT,
    GL_UNSIGNED_INT,
    GL_INT,
    GL_HALF_FLOAT,
    GL_FLOAT,
    GL_UNSIGNED_INT_2_10_10_10_REV,
    GL_UNSIGNED_INT_10F_11F_11F_REV,
    GL_UNSIGNED_INT_5_9_9_9_REV,
    GL_UNSIGNED_INT_24_8,
};

// ES2 enums
static const FormatType kSupportedFormatTypesES2[] = {
    { GL_RGB, GL_RGB, GL_UNSIGNED_BYTE },
    { GL_RGB, GL_RGB, GL_UNSIGNED_SHORT_5_6_5 },
    { GL_RGBA, GL_RGBA, GL_UNSIGNED_BYTE },
    { GL_RGBA, GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4 },
    { GL_RGBA, GL_RGBA, GL_UNSIGNED_SHORT_5_5_5_1 },
    { GL_LUMINANCE_ALPHA, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE },
    { GL_LUMINANCE, GL_LUMINANCE, GL_UNSIGNED_BYTE },
    { GL_ALPHA, GL_ALPHA, GL_UNSIGNED_BYTE },
};

// Exposed by GL_OES_texture_float
static const FormatType kSupportedFormatTypesOESTexFloat[] = {
    { GL_RGB, GL_RGB, GL_FLOAT },
    { GL_RGBA, GL_RGBA, GL_FLOAT },
    { GL_LUMINANCE_ALPHA, GL_LUMINANCE_ALPHA, GL_FLOAT },
    { GL_LUMINANCE, GL_LUMINANCE, GL_FLOAT },
    { GL_ALPHA, GL_ALPHA, GL_FLOAT },
};

// Exposed by GL_OES_texture_half_float
static const FormatType kSupportedFormatTypesOESTexHalfFloat[] = {
    { GL_RGB, GL_RGB, GL_HALF_FLOAT_OES },
    { GL_RGBA, GL_RGBA, GL_HALF_FLOAT_OES },
    { GL_LUMINANCE_ALPHA, GL_LUMINANCE_ALPHA, GL_HALF_FLOAT_OES },
    { GL_LUMINANCE, GL_LUMINANCE, GL_HALF_FLOAT_OES },
    { GL_ALPHA, GL_ALPHA, GL_HALF_FLOAT_OES },
};

// Exposed by GL_ANGLE_depth_texture
static const FormatType kSupportedFormatTypesOESDepthTex[] = {
    { GL_DEPTH_COMPONENT, GL_DEPTH_COMPONENT, GL_UNSIGNED_SHORT },
    { GL_DEPTH_COMPONENT, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT },
    { GL_DEPTH_STENCIL, GL_DEPTH_STENCIL, GL_UNSIGNED_INT_24_8 },
};

// Exposed by GL_EXT_sRGB
static const FormatType kSupportedFormatTypesEXTsRGB[] = {
    { GL_SRGB, GL_SRGB, GL_UNSIGNED_BYTE },
    { GL_SRGB_ALPHA_EXT, GL_SRGB_ALPHA_EXT, GL_UNSIGNED_BYTE },
};

// ES3 enums
static const FormatType kSupportedFormatTypesES3[] = {
    { GL_R8, GL_RED, GL_UNSIGNED_BYTE },
    { GL_R8_SNORM, GL_RED, GL_BYTE },
    { GL_R16F, GL_RED, GL_HALF_FLOAT },
    { GL_R16F, GL_RED, GL_FLOAT },
    { GL_R32F, GL_RED, GL_FLOAT },
    { GL_R8UI, GL_RED_INTEGER, GL_UNSIGNED_BYTE },
    { GL_R8I, GL_RED_INTEGER, GL_BYTE },
    { GL_R16UI, GL_RED_INTEGER, GL_UNSIGNED_SHORT },
    { GL_R16I, GL_RED_INTEGER, GL_SHORT },
    { GL_R32UI, GL_RED_INTEGER, GL_UNSIGNED_INT },
    { GL_R32I, GL_RED_INTEGER, GL_INT },
    { GL_RG8, GL_RG, GL_UNSIGNED_BYTE },
    { GL_RG8_SNORM, GL_RG, GL_BYTE },
    { GL_RG16F, GL_RG, GL_HALF_FLOAT },
    { GL_RG16F, GL_RG, GL_FLOAT },
    { GL_RG32F, GL_RG, GL_FLOAT },
    { GL_RG8UI, GL_RG_INTEGER, GL_UNSIGNED_BYTE },
    { GL_RG8I, GL_RG_INTEGER, GL_BYTE },
    { GL_RG16UI, GL_RG_INTEGER, GL_UNSIGNED_SHORT },
    { GL_RG16I, GL_RG_INTEGER, GL_SHORT },
    { GL_RG32UI, GL_RG_INTEGER, GL_UNSIGNED_INT },
    { GL_RG32I, GL_RG_INTEGER, GL_INT },
    { GL_RGB8, GL_RGB, GL_UNSIGNED_BYTE },
    { GL_SRGB8, GL_RGB, GL_UNSIGNED_BYTE },
    { GL_RGB565, GL_RGB, GL_UNSIGNED_BYTE, },
    { GL_RGB565, GL_RGB, GL_UNSIGNED_SHORT_5_6_5 },
    { GL_RGB8_SNORM, GL_RGB, GL_BYTE },
    { GL_R11F_G11F_B10F, GL_RGB, GL_UNSIGNED_INT_10F_11F_11F_REV },
    { GL_R11F_G11F_B10F, GL_RGB, GL_HALF_FLOAT },
    { GL_R11F_G11F_B10F, GL_RGB, GL_FLOAT },
    { GL_RGB9_E5, GL_RGB, GL_UNSIGNED_INT_5_9_9_9_REV },
    { GL_RGB9_E5, GL_RGB, GL_HALF_FLOAT },
    { GL_RGB9_E5, GL_RGB, GL_FLOAT },
    { GL_RGB16F, GL_RGB, GL_HALF_FLOAT },
    { GL_RGB16F, GL_RGB, GL_FLOAT },
    { GL_RGB32F, GL_RGB, GL_FLOAT },
    { GL_RGB8UI, GL_RGB_INTEGER, GL_UNSIGNED_BYTE },
    { GL_RGB8I, GL_RGB_INTEGER, GL_BYTE },
    { GL_RGB16UI, GL_RGB_INTEGER, GL_UNSIGNED_SHORT },
    { GL_RGB16I, GL_RGB_INTEGER, GL_SHORT },
    { GL_RGB32UI, GL_RGB_INTEGER, GL_UNSIGNED_INT },
    { GL_RGB32I, GL_RGB_INTEGER, GL_INT },
    { GL_RGBA8, GL_RGBA, GL_UNSIGNED_BYTE },
    { GL_SRGB8_ALPHA8, GL_RGBA, GL_UNSIGNED_BYTE },
    { GL_RGBA8_SNORM, GL_RGBA, GL_BYTE },
    { GL_RGB5_A1, GL_RGBA, GL_UNSIGNED_BYTE },
    { GL_RGB5_A1, GL_RGBA, GL_UNSIGNED_SHORT_5_5_5_1 },
    { GL_RGB5_A1, GL_RGBA, GL_UNSIGNED_INT_2_10_10_10_REV },
    { GL_RGBA4, GL_RGBA, GL_UNSIGNED_BYTE },
    { GL_RGBA4, GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4 },
    { GL_RGB10_A2, GL_RGBA, GL_UNSIGNED_INT_2_10_10_10_REV },
    { GL_RGBA16F, GL_RGBA, GL_HALF_FLOAT },
    { GL_RGBA16F, GL_RGBA, GL_FLOAT },
    { GL_RGBA32F, GL_RGBA, GL_FLOAT },
    { GL_RGBA8UI, GL_RGBA_INTEGER, GL_UNSIGNED_BYTE },
    { GL_RGBA8I, GL_RGBA_INTEGER, GL_BYTE },
    { GL_RGB10_A2UI, GL_RGBA_INTEGER, GL_UNSIGNED_INT_2_10_10_10_REV },
    { GL_RGBA16UI, GL_RGBA_INTEGER, GL_UNSIGNED_SHORT },
    { GL_RGBA16I, GL_RGBA_INTEGER, GL_SHORT },
    { GL_RGBA32I, GL_RGBA_INTEGER, GL_INT },
    { GL_RGBA32UI, GL_RGBA_INTEGER, GL_UNSIGNED_INT },
    { GL_DEPTH_COMPONENT16, GL_DEPTH_COMPONENT, GL_UNSIGNED_SHORT },
    { GL_DEPTH_COMPONENT16, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT },
    { GL_DEPTH_COMPONENT24, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT },
    { GL_DEPTH_COMPONENT32F, GL_DEPTH_COMPONENT, GL_FLOAT },
    { GL_DEPTH24_STENCIL8, GL_DEPTH_STENCIL, GL_UNSIGNED_INT_24_8 },
};

} // namespace anonymous

#define ADD_VALUES_TO_SET(set, values) \
    for (size_t i = 0; i < arraysize(values); ++i) {   \
        set.insert(values[i]);                         \
    }

WebGLRenderingContextBase::WebGLRenderingContextBase(HTMLCanvasElement* passedCanvas, PassOwnPtr<WebGraphicsContext3D> context, const WebGLContextAttributes& requestedAttributes)
    : CanvasRenderingContext(passedCanvas)
    , m_contextLostMode(NotLostContext)
    , m_autoRecoveryMethod(Manual)
    , m_dispatchContextLostEventTimer(this, &WebGLRenderingContextBase::dispatchContextLostEvent)
    , m_restoreAllowed(false)
    , m_restoreTimer(this, &WebGLRenderingContextBase::maybeRestoreContext)
    , m_generatedImageCache(4)
    , m_requestedAttributes(requestedAttributes)
    , m_synthesizedErrorsToConsole(true)
    , m_numGLErrorsToConsoleAllowed(maxGLErrorsAllowedToConsole)
    , m_multisamplingAllowed(false)
    , m_multisamplingObserverRegistered(false)
    , m_onePlusMaxNonDefaultTextureUnit(0)
    , m_isWebGL2FormatsTypesAdded(false)
    , m_isOESTextureFloatFormatsTypesAdded(false)
    , m_isOESTextureHalfFloatFormatsTypesAdded(false)
    , m_isWebGLDepthTextureFormatsTypesAdded(false)
    , m_isEXTsRGBFormatsTypesAdded(false)
{
    ASSERT(context);

    m_contextGroup = WebGLContextGroup::create();
    m_contextGroup->addContext(this);

    m_maxViewportDims[0] = m_maxViewportDims[1] = 0;
    context->getIntegerv(GL_MAX_VIEWPORT_DIMS, m_maxViewportDims);

    RefPtr<DrawingBuffer> buffer = createDrawingBuffer(context);
    if (!buffer) {
        m_contextLostMode = SyntheticLostContext;
        return;
    }

    m_drawingBuffer = buffer.release();

    drawingBuffer()->bind(GL_FRAMEBUFFER);
    setupFlags();

    ADD_VALUES_TO_SET(m_supportedInternalFormats, kSupportedInternalFormatsES2);
    ADD_VALUES_TO_SET(m_supportedFormats, kSupportedFormatsES2);
    ADD_VALUES_TO_SET(m_supportedTypes, kSupportedTypesES2);
    ADD_VALUES_TO_SET(m_supportedFormatTypeCombinations, kSupportedFormatTypesES2);
}

PassRefPtr<DrawingBuffer> WebGLRenderingContextBase::createDrawingBuffer(PassOwnPtr<WebGraphicsContext3D> context)
{
    WebGraphicsContext3D::Attributes attrs;
    attrs.alpha = m_requestedAttributes.alpha();
    attrs.depth = m_requestedAttributes.depth();
    attrs.stencil = m_requestedAttributes.stencil();
    attrs.antialias = m_requestedAttributes.antialias();
    attrs.premultipliedAlpha = m_requestedAttributes.premultipliedAlpha();
    DrawingBuffer::PreserveDrawingBuffer preserve = m_requestedAttributes.preserveDrawingBuffer() ? DrawingBuffer::Preserve : DrawingBuffer::Discard;
    return DrawingBuffer::create(context, clampedCanvasSize(), preserve, attrs);
}

void WebGLRenderingContextBase::initializeNewContext()
{
    ASSERT(!isContextLost());
    ASSERT(drawingBuffer());

    m_markedCanvasDirty = false;
    m_activeTextureUnit = 0;
    m_packAlignment = 4;
    m_unpackAlignment = 4;
    m_unpackFlipY = false;
    m_unpackPremultiplyAlpha = false;
    m_unpackColorspaceConversion = GC3D_BROWSER_DEFAULT_WEBGL;
    m_boundArrayBuffer = nullptr;
    m_currentProgram = nullptr;
    m_framebufferBinding = nullptr;
    m_renderbufferBinding = nullptr;
    m_valuebufferBinding = nullptr;
    m_depthMask = true;
    m_stencilEnabled = false;
    m_stencilMask = 0xFFFFFFFF;
    m_stencilMaskBack = 0xFFFFFFFF;
    m_stencilFuncRef = 0;
    m_stencilFuncRefBack = 0;
    m_stencilFuncMask = 0xFFFFFFFF;
    m_stencilFuncMaskBack = 0xFFFFFFFF;
    m_numGLErrorsToConsoleAllowed = maxGLErrorsAllowedToConsole;

    m_clearColor[0] = m_clearColor[1] = m_clearColor[2] = m_clearColor[3] = 0;
    m_scissorEnabled = false;
    m_clearDepth = 1;
    m_clearStencil = 0;
    m_colorMask[0] = m_colorMask[1] = m_colorMask[2] = m_colorMask[3] = true;

    GLint numCombinedTextureImageUnits = 0;
    webContext()->getIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &numCombinedTextureImageUnits);
    m_textureUnits.clear();
    m_textureUnits.resize(numCombinedTextureImageUnits);

    GLint numVertexAttribs = 0;
    webContext()->getIntegerv(GL_MAX_VERTEX_ATTRIBS, &numVertexAttribs);
    m_maxVertexAttribs = numVertexAttribs;

    m_maxTextureSize = 0;
    webContext()->getIntegerv(GL_MAX_TEXTURE_SIZE, &m_maxTextureSize);
    m_maxTextureLevel = WebGLTexture::computeLevelCount(m_maxTextureSize, m_maxTextureSize, 1);
    m_maxCubeMapTextureSize = 0;
    webContext()->getIntegerv(GL_MAX_CUBE_MAP_TEXTURE_SIZE, &m_maxCubeMapTextureSize);
    m_maxCubeMapTextureLevel = WebGLTexture::computeLevelCount(m_maxCubeMapTextureSize, m_maxCubeMapTextureSize, 1);
    m_maxRenderbufferSize = 0;
    webContext()->getIntegerv(GL_MAX_RENDERBUFFER_SIZE, &m_maxRenderbufferSize);

    // These two values from EXT_draw_buffers are lazily queried.
    m_maxDrawBuffers = 0;
    m_maxColorAttachments = 0;

    m_backDrawBuffer = GL_BACK;

    m_readBufferOfDefaultFramebuffer = GL_BACK;

    if (isWebGL2OrHigher()) {
        m_defaultVertexArrayObject = WebGLVertexArrayObject::create(this, WebGLVertexArrayObjectBase::VaoTypeDefault);
    } else {
        m_defaultVertexArrayObject = WebGLVertexArrayObjectOES::create(this, WebGLVertexArrayObjectBase::VaoTypeDefault);
    }
    addContextObject(m_defaultVertexArrayObject.get());
    m_boundVertexArrayObject = m_defaultVertexArrayObject;

    m_vertexAttribValue.resize(m_maxVertexAttribs);

    createFallbackBlackTextures1x1();

    webContext()->viewport(0, 0, drawingBufferWidth(), drawingBufferHeight());
    webContext()->scissor(0, 0, drawingBufferWidth(), drawingBufferHeight());

    m_contextLostCallbackAdapter = WebGLRenderingContextLostCallback::create(this);
    m_errorMessageCallbackAdapter = WebGLRenderingContextErrorMessageCallback::create(this);

    webContext()->setContextLostCallback(m_contextLostCallbackAdapter.get());
    webContext()->setErrorMessageCallback(m_errorMessageCallbackAdapter.get());

    // This ensures that the context has a valid "lastFlushID" and won't be mistakenly identified as the "least recently used" context.
    webContext()->flush();

    for (int i = 0; i < WebGLExtensionNameCount; ++i)
        m_extensionEnabled[i] = false;

    m_isWebGL2FormatsTypesAdded = false;
    m_isOESTextureFloatFormatsTypesAdded = false;
    m_isOESTextureHalfFloatFormatsTypesAdded = false;
    m_isWebGLDepthTextureFormatsTypesAdded = false;
    m_isEXTsRGBFormatsTypesAdded = false;

    m_supportedInternalFormats.clear();
    ADD_VALUES_TO_SET(m_supportedInternalFormats, kSupportedInternalFormatsES2);
    m_supportedFormats.clear();
    ADD_VALUES_TO_SET(m_supportedFormats, kSupportedFormatsES2);
    m_supportedTypes.clear();
    ADD_VALUES_TO_SET(m_supportedTypes, kSupportedTypesES2);
    m_supportedFormatTypeCombinations.clear();
    ADD_VALUES_TO_SET(m_supportedFormatTypeCombinations, kSupportedFormatTypesES2);

    activateContext(this);
}

void WebGLRenderingContextBase::setupFlags()
{
    ASSERT(drawingBuffer());
    if (Page* p = canvas()->document().page()) {
        m_synthesizedErrorsToConsole = p->settings().webGLErrorsToConsoleEnabled();

        if (!m_multisamplingObserverRegistered && m_requestedAttributes.antialias()) {
            m_multisamplingAllowed = drawingBuffer()->multisample();
            p->addMultisamplingChangedObserver(this);
            m_multisamplingObserverRegistered = true;
        }
    }

    m_isDepthStencilSupported = extensionsUtil()->isExtensionEnabled("GL_OES_packed_depth_stencil");
}

void WebGLRenderingContextBase::addCompressedTextureFormat(GLenum format)
{
    if (!m_compressedTextureFormats.contains(format))
        m_compressedTextureFormats.append(format);
}

void WebGLRenderingContextBase::removeAllCompressedTextureFormats()
{
    m_compressedTextureFormats.clear();
}

// Helper function for V8 bindings to identify what version of WebGL a CanvasRenderingContext supports.
unsigned WebGLRenderingContextBase::getWebGLVersion(const CanvasRenderingContext* context)
{
    if (!context->is3d())
        return 0;
    return static_cast<const WebGLRenderingContextBase*>(context)->version();
}

WebGLRenderingContextBase::~WebGLRenderingContextBase()
{
    // Remove all references to WebGLObjects so if they are the last reference
    // they will be freed before the last context is removed from the context group.
    m_boundArrayBuffer = nullptr;
    m_defaultVertexArrayObject = nullptr;
    m_boundVertexArrayObject = nullptr;
    m_vertexAttrib0Buffer = nullptr;
    m_currentProgram = nullptr;
    m_framebufferBinding = nullptr;
    m_renderbufferBinding = nullptr;
    m_valuebufferBinding = nullptr;

    // WebGLTexture shared objects will be detached and deleted
    // m_contextGroup->removeContext(this), which will bring about deleteTexture() calls.
    // We null these out to avoid accessing those members in deleteTexture().
    for (size_t i = 0; i < m_textureUnits.size(); ++i) {
        m_textureUnits[i].m_texture2DBinding = nullptr;
        m_textureUnits[i].m_textureCubeMapBinding = nullptr;
        m_textureUnits[i].m_texture3DBinding = nullptr;
        m_textureUnits[i].m_texture2DArrayBinding = nullptr;
    }

    m_blackTexture2D = nullptr;
    m_blackTextureCubeMap = nullptr;

    detachAndRemoveAllObjects();

    // Release all extensions now.
    for (ExtensionTracker* tracker : m_extensions) {
        tracker->loseExtension(true);
    }
    m_extensions.clear();

    // Context must be removed from the group prior to the destruction of the
    // WebGraphicsContext3D, otherwise shared objects may not be properly deleted.
    m_contextGroup->removeContext(this);

    destroyContext();

    if (m_multisamplingObserverRegistered)
        if (Page* page = canvas()->document().page())
            page->removeMultisamplingChangedObserver(this);

    willDestroyContext(this);
}

void WebGLRenderingContextBase::destroyContext()
{
    if (!drawingBuffer())
        return;

    m_extensionsUtil.clear();

    webContext()->setContextLostCallback(nullptr);
    webContext()->setErrorMessageCallback(nullptr);

    ASSERT(drawingBuffer());
    m_drawingBuffer->beginDestruction();
    m_drawingBuffer.clear();
}

void WebGLRenderingContextBase::markContextChanged(ContentChangeType changeType)
{
    if (m_framebufferBinding || isContextLost())
        return;

    drawingBuffer()->markContentsChanged();

    LayoutBox* layoutBox = canvas()->layoutBox();
    if (layoutBox && layoutBox->hasAcceleratedCompositing()) {
        m_markedCanvasDirty = true;
        canvas()->clearCopiedImage();
        layoutBox->contentChanged(changeType);
    } else {
        if (!m_markedCanvasDirty) {
            m_markedCanvasDirty = true;
            canvas()->didDraw(FloatRect(FloatPoint(0, 0), clampedCanvasSize()));
        }
    }
}

WebGLRenderingContextBase::HowToClear WebGLRenderingContextBase::clearIfComposited(GLbitfield mask)
{
    if (isContextLost())
        return Skipped;

    if (!drawingBuffer()->bufferClearNeeded() || (mask && m_framebufferBinding))
        return Skipped;

    Nullable<WebGLContextAttributes> contextAttributes;
    getContextAttributes(contextAttributes);
    if (contextAttributes.isNull()) {
        // Unlikely, but context was lost.
        return Skipped;
    }

    // Determine if it's possible to combine the clear the user asked for and this clear.
    bool combinedClear = mask && !m_scissorEnabled;

    webContext()->disable(GL_SCISSOR_TEST);
    if (combinedClear && (mask & GL_COLOR_BUFFER_BIT)) {
        webContext()->clearColor(m_colorMask[0] ? m_clearColor[0] : 0,
            m_colorMask[1] ? m_clearColor[1] : 0,
            m_colorMask[2] ? m_clearColor[2] : 0,
            m_colorMask[3] ? m_clearColor[3] : 0);
    } else {
        webContext()->clearColor(0, 0, 0, 0);
    }
    webContext()->colorMask(true, true, true, true);
    GLbitfield clearMask = GL_COLOR_BUFFER_BIT;
    if (contextAttributes.get().depth()) {
        if (!combinedClear || !m_depthMask || !(mask & GL_DEPTH_BUFFER_BIT))
            webContext()->clearDepth(1.0f);
        clearMask |= GL_DEPTH_BUFFER_BIT;
        webContext()->depthMask(true);
    }
    if (contextAttributes.get().stencil()) {
        if (combinedClear && (mask & GL_STENCIL_BUFFER_BIT))
            webContext()->clearStencil(m_clearStencil & m_stencilMask);
        else
            webContext()->clearStencil(0);
        clearMask |= GL_STENCIL_BUFFER_BIT;
        webContext()->stencilMaskSeparate(GL_FRONT, 0xFFFFFFFF);
    }

    drawingBuffer()->clearFramebuffers(clearMask);

    restoreStateAfterClear();
    drawingBuffer()->restoreFramebufferBindings();
    drawingBuffer()->setBufferClearNeeded(false);

    return combinedClear ? CombinedClear : JustClear;
}

void WebGLRenderingContextBase::restoreStateAfterClear()
{
    if (isContextLost())
        return;

    // Restore the state that the context set.
    if (m_scissorEnabled)
        webContext()->enable(GL_SCISSOR_TEST);
    webContext()->clearColor(m_clearColor[0], m_clearColor[1],
        m_clearColor[2], m_clearColor[3]);
    webContext()->colorMask(m_colorMask[0], m_colorMask[1],
        m_colorMask[2], m_colorMask[3]);
    webContext()->clearDepth(m_clearDepth);
    webContext()->clearStencil(m_clearStencil);
    webContext()->stencilMaskSeparate(GL_FRONT, m_stencilMask);
    webContext()->depthMask(m_depthMask);
}

void WebGLRenderingContextBase::markLayerComposited()
{
    if (!isContextLost())
        drawingBuffer()->setBufferClearNeeded(true);
}

void WebGLRenderingContextBase::setIsHidden(bool hidden)
{
    if (drawingBuffer())
        drawingBuffer()->setIsHidden(hidden);
}

bool WebGLRenderingContextBase::paintRenderingResultsToCanvas(SourceDrawingBuffer sourceBuffer)
{
    if (isContextLost())
        return false;

    bool mustClearNow = clearIfComposited() != Skipped;
    if (!m_markedCanvasDirty && !mustClearNow)
        return false;

    canvas()->clearCopiedImage();
    m_markedCanvasDirty = false;

    ScopedTexture2DRestorer restorer(this);
    ScopedFramebufferRestorer fboRestorer(this);

    drawingBuffer()->commit();
    if (!canvas()->buffer()->copyRenderingResultsFromDrawingBuffer(drawingBuffer(), sourceBuffer)) {
        canvas()->ensureUnacceleratedImageBuffer();
        if (canvas()->hasImageBuffer())
            drawingBuffer()->paintRenderingResultsToCanvas(canvas()->buffer());
    }

    return true;
}

ImageData* WebGLRenderingContextBase::paintRenderingResultsToImageData(SourceDrawingBuffer sourceBuffer)
{
    if (isContextLost())
        return nullptr;
    if (m_requestedAttributes.premultipliedAlpha())
        return nullptr;

    clearIfComposited();
    drawingBuffer()->commit();
    ScopedFramebufferRestorer restorer(this);
    int width, height;
    WTF::ArrayBufferContents contents;
    if (!drawingBuffer()->paintRenderingResultsToImageData(width, height, sourceBuffer, contents))
        return nullptr;
    RefPtr<DOMArrayBuffer> imageDataPixels = DOMArrayBuffer::create(contents);

    return ImageData::create(
        IntSize(width, height),
        DOMUint8ClampedArray::create(imageDataPixels, 0, imageDataPixels->byteLength()));
}

void WebGLRenderingContextBase::reshape(int width, int height)
{
    if (isContextLost())
        return;

    // This is an approximation because at WebGLRenderingContextBase level we don't
    // know if the underlying FBO uses textures or renderbuffers.
    GLint maxSize = std::min(m_maxTextureSize, m_maxRenderbufferSize);
    GLint maxWidth = std::min(maxSize, m_maxViewportDims[0]);
    GLint maxHeight = std::min(maxSize, m_maxViewportDims[1]);
    width = clamp(width, 1, maxWidth);
    height = clamp(height, 1, maxHeight);

    // Limit drawing buffer area to 4k*4k to avoid memory exhaustion. Width or height may be larger than
    // 4k as long as it's within the max viewport dimensions and total area remains within the limit.
    // For example: 5120x2880 should be fine.
    const int maxArea = 4096 * 4096;
    int currentArea = width * height;
    if (currentArea > maxArea) {
        // If we've exceeded the area limit scale the buffer down, preserving ascpect ratio, until it fits.
        float scaleFactor = sqrtf(static_cast<float>(maxArea) / static_cast<float>(currentArea));
        width = std::max(1, static_cast<int>(width * scaleFactor));
        height = std::max(1, static_cast<int>(height * scaleFactor));
    }

    // We don't have to mark the canvas as dirty, since the newly created image buffer will also start off
    // clear (and this matches what reshape will do).
    drawingBuffer()->reset(IntSize(width, height));
    restoreStateAfterClear();

    webContext()->bindTexture(GL_TEXTURE_2D, objectOrZero(m_textureUnits[m_activeTextureUnit].m_texture2DBinding.get()));
    webContext()->bindRenderbuffer(GL_RENDERBUFFER, objectOrZero(m_renderbufferBinding.get()));
    drawingBuffer()->restoreFramebufferBindings();
}

int WebGLRenderingContextBase::drawingBufferWidth() const
{
    return isContextLost() ? 0 : drawingBuffer()->size().width();
}

int WebGLRenderingContextBase::drawingBufferHeight() const
{
    return isContextLost() ? 0 : drawingBuffer()->size().height();
}

unsigned WebGLRenderingContextBase::sizeInBytes(GLenum type)
{
    switch (type) {
    case GL_BYTE:
        return sizeof(GLbyte);
    case GL_UNSIGNED_BYTE:
        return sizeof(GLubyte);
    case GL_SHORT:
        return sizeof(GLshort);
    case GL_UNSIGNED_SHORT:
        return sizeof(GLushort);
    case GL_INT:
        return sizeof(GLint);
    case GL_UNSIGNED_INT:
        return sizeof(GLuint);
    case GL_FLOAT:
        return sizeof(GLfloat);
    }
    ASSERT_NOT_REACHED();
    return 0;
}

void WebGLRenderingContextBase::activeTexture(GLenum texture)
{
    if (isContextLost())
        return;
    if (texture - GL_TEXTURE0 >= m_textureUnits.size()) {
        synthesizeGLError(GL_INVALID_ENUM, "activeTexture", "texture unit out of range");
        return;
    }
    m_activeTextureUnit = texture - GL_TEXTURE0;
    webContext()->activeTexture(texture);

    drawingBuffer()->setActiveTextureUnit(texture);

}

void WebGLRenderingContextBase::attachShader(WebGLProgram* program, WebGLShader* shader)
{
    if (isContextLost() || !validateWebGLObject("attachShader", program) || !validateWebGLObject("attachShader", shader))
        return;
    if (!program->attachShader(shader)) {
        synthesizeGLError(GL_INVALID_OPERATION, "attachShader", "shader attachment already has shader");
        return;
    }
    webContext()->attachShader(objectOrZero(program), objectOrZero(shader));
    shader->onAttached();
}

void WebGLRenderingContextBase::bindAttribLocation(WebGLProgram* program, GLuint index, const String& name)
{
    if (isContextLost() || !validateWebGLObject("bindAttribLocation", program))
        return;
    if (!validateLocationLength("bindAttribLocation", name))
        return;
    if (!validateString("bindAttribLocation", name))
        return;
    if (isPrefixReserved(name)) {
        synthesizeGLError(GL_INVALID_OPERATION, "bindAttribLocation", "reserved prefix");
        return;
    }
    if (index >= m_maxVertexAttribs) {
        synthesizeGLError(GL_INVALID_VALUE, "bindAttribLocation", "index out of range");
        return;
    }
    webContext()->bindAttribLocation(objectOrZero(program), index, name.utf8().data());
}

bool WebGLRenderingContextBase::checkObjectToBeBound(const char* functionName, WebGLObject* object, bool& deleted)
{
    deleted = false;
    if (isContextLost())
        return false;
    if (object) {
        if (!object->validate(contextGroup(), this)) {
            synthesizeGLError(GL_INVALID_OPERATION, functionName, "object not from this context");
            return false;
        }
        deleted = !object->hasObject();
    }
    return true;
}

bool WebGLRenderingContextBase::validateAndUpdateBufferBindTarget(const char* functionName, GLenum target, WebGLBuffer* buffer)
{
    if (!validateBufferTarget(functionName, target))
        return false;

    if (buffer && buffer->getInitialTarget() && buffer->getInitialTarget() != target) {
        synthesizeGLError(GL_INVALID_OPERATION, functionName, "buffers can not be used with multiple targets");
        return false;
    }

    switch (target) {
    case GL_ARRAY_BUFFER:
        m_boundArrayBuffer = buffer;
        break;
    case GL_ELEMENT_ARRAY_BUFFER:
        m_boundVertexArrayObject->setElementArrayBuffer(buffer);
        break;
    default:
        ASSERT_NOT_REACHED();
        return false;
    }

    if (buffer && !buffer->getInitialTarget())
        buffer->setInitialTarget(target);
    return true;
}

void WebGLRenderingContextBase::bindBuffer(GLenum target, WebGLBuffer* buffer)
{
    bool deleted;
    if (!checkObjectToBeBound("bindBuffer", buffer, deleted))
        return;
    if (deleted)
        buffer = 0;
    if (!validateAndUpdateBufferBindTarget("bindBuffer", target, buffer))
        return;

    webContext()->bindBuffer(target, objectOrZero(buffer));
}

void WebGLRenderingContextBase::bindFramebuffer(GLenum target, WebGLFramebuffer* buffer)
{
    bool deleted;
    if (!checkObjectToBeBound("bindFramebuffer", buffer, deleted))
        return;

    if (deleted)
        buffer = 0;

    if (target != GL_FRAMEBUFFER) {
        synthesizeGLError(GL_INVALID_ENUM, "bindFramebuffer", "invalid target");
        return;
    }

    setFramebuffer(target, buffer);
}

void WebGLRenderingContextBase::bindRenderbuffer(GLenum target, WebGLRenderbuffer* renderBuffer)
{
    bool deleted;
    if (!checkObjectToBeBound("bindRenderbuffer", renderBuffer, deleted))
        return;
    if (deleted)
        renderBuffer = 0;
    if (target != GL_RENDERBUFFER) {
        synthesizeGLError(GL_INVALID_ENUM, "bindRenderbuffer", "invalid target");
        return;
    }
    m_renderbufferBinding = renderBuffer;
    webContext()->bindRenderbuffer(target, objectOrZero(renderBuffer));
    if (renderBuffer)
        renderBuffer->setHasEverBeenBound();
}

void WebGLRenderingContextBase::bindTexture(GLenum target, WebGLTexture* texture)
{
    bool deleted;
    if (!checkObjectToBeBound("bindTexture", texture, deleted))
        return;
    if (deleted)
        texture = 0;
    if (texture && texture->getTarget() && texture->getTarget() != target) {
        synthesizeGLError(GL_INVALID_OPERATION, "bindTexture", "textures can not be used with multiple targets");
        return;
    }
    if (target == GL_TEXTURE_2D) {
        m_textureUnits[m_activeTextureUnit].m_texture2DBinding = texture;

        if (!m_activeTextureUnit)
            drawingBuffer()->setTexture2DBinding(objectOrZero(texture));
    } else if (target == GL_TEXTURE_CUBE_MAP) {
        m_textureUnits[m_activeTextureUnit].m_textureCubeMapBinding = texture;
    } else if (isWebGL2OrHigher() && target == GL_TEXTURE_2D_ARRAY) {
        m_textureUnits[m_activeTextureUnit].m_texture2DArrayBinding = texture;
    } else if (isWebGL2OrHigher() && target == GL_TEXTURE_3D) {
        m_textureUnits[m_activeTextureUnit].m_texture3DBinding = texture;
    } else {
        synthesizeGLError(GL_INVALID_ENUM, "bindTexture", "invalid target");
        return;
    }

    webContext()->bindTexture(target, objectOrZero(texture));
    if (texture) {
        texture->setTarget(target, getMaxTextureLevelForTarget(target));
        m_onePlusMaxNonDefaultTextureUnit = max(m_activeTextureUnit + 1, m_onePlusMaxNonDefaultTextureUnit);
    } else {
        // If the disabled index is the current maximum, trace backwards to find the new max enabled texture index
        if (m_onePlusMaxNonDefaultTextureUnit == m_activeTextureUnit + 1) {
            findNewMaxNonDefaultTextureUnit();
        }
    }

    // Note: previously we used to automatically set the TEXTURE_WRAP_R
    // repeat mode to CLAMP_TO_EDGE for cube map textures, because OpenGL
    // ES 2.0 doesn't expose this flag (a bug in the specification) and
    // otherwise the application has no control over the seams in this
    // dimension. However, it appears that supporting this properly on all
    // platforms is fairly involved (will require a HashMap from texture ID
    // in all ports), and we have not had any complaints, so the logic has
    // been removed.

}

void WebGLRenderingContextBase::blendColor(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha)
{
    if (isContextLost())
        return;
    webContext()->blendColor(red, green, blue, alpha);
}

void WebGLRenderingContextBase::blendEquation(GLenum mode)
{
    if (isContextLost() || !validateBlendEquation("blendEquation", mode))
        return;
    webContext()->blendEquation(mode);
}

void WebGLRenderingContextBase::blendEquationSeparate(GLenum modeRGB, GLenum modeAlpha)
{
    if (isContextLost() || !validateBlendEquation("blendEquationSeparate", modeRGB) || !validateBlendEquation("blendEquationSeparate", modeAlpha))
        return;
    webContext()->blendEquationSeparate(modeRGB, modeAlpha);
}


void WebGLRenderingContextBase::blendFunc(GLenum sfactor, GLenum dfactor)
{
    if (isContextLost() || !validateBlendFuncFactors("blendFunc", sfactor, dfactor))
        return;
    webContext()->blendFunc(sfactor, dfactor);
}

void WebGLRenderingContextBase::blendFuncSeparate(GLenum srcRGB, GLenum dstRGB, GLenum srcAlpha, GLenum dstAlpha)
{
    // Note: Alpha does not have the same restrictions as RGB.
    if (isContextLost() || !validateBlendFuncFactors("blendFuncSeparate", srcRGB, dstRGB))
        return;
    webContext()->blendFuncSeparate(srcRGB, dstRGB, srcAlpha, dstAlpha);
}

void WebGLRenderingContextBase::bufferDataImpl(GLenum target, long long size, const void* data, GLenum usage)
{
    WebGLBuffer* buffer = validateBufferDataTarget("bufferData", target);
    if (!buffer)
        return;

    if (!validateBufferDataUsage("bufferData", usage))
        return;

    if (!validateValueFitNonNegInt32("bufferData", "size", size))
        return;

    buffer->setSize(size);

    webContext()->bufferData(target, static_cast<GLsizeiptr>(size), data, usage);
}

void WebGLRenderingContextBase::bufferData(GLenum target, long long size, GLenum usage)
{
    if (isContextLost())
        return;
    bufferDataImpl(target, size, 0, usage);
}

void WebGLRenderingContextBase::bufferData(GLenum target, DOMArrayBuffer* data, GLenum usage)
{
    if (isContextLost())
        return;
    if (!data) {
        synthesizeGLError(GL_INVALID_VALUE, "bufferData", "no data");
        return;
    }
    bufferDataImpl(target, data->byteLength(), data->data(), usage);
}

void WebGLRenderingContextBase::bufferData(GLenum target, DOMArrayBufferView* data, GLenum usage)
{
    if (isContextLost())
        return;
    if (!data) {
        synthesizeGLError(GL_INVALID_VALUE, "bufferData", "no data");
        return;
    }
    bufferDataImpl(target, data->byteLength(), data->baseAddress(), usage);
}

void WebGLRenderingContextBase::bufferSubDataImpl(GLenum target, long long offset, GLsizeiptr size, const void* data)
{
    WebGLBuffer* buffer = validateBufferDataTarget("bufferSubData", target);
    if (!buffer)
        return;
    if (!validateValueFitNonNegInt32("bufferSubData", "offset", offset))
        return;
    if (!data)
        return;
    if (offset + static_cast<long long>(size) > buffer->getSize()) {
        synthesizeGLError(GL_INVALID_VALUE, "bufferSubData", "buffer overflow");
        return;
    }

    webContext()->bufferSubData(target, static_cast<GLintptr>(offset), size, data);
}

void WebGLRenderingContextBase::bufferSubData(GLenum target, long long offset, DOMArrayBuffer* data)
{
    if (isContextLost())
        return;
    if (!data)
        return;
    bufferSubDataImpl(target, offset, data->byteLength(), data->data());
}

void WebGLRenderingContextBase::bufferSubData(GLenum target, long long offset, const FlexibleArrayBufferView& data)
{
    if (isContextLost())
        return;
    if (!data)
        return;
    bufferSubDataImpl(target, offset, data.byteLength(), data.baseAddressMaybeOnStack());
}

bool WebGLRenderingContextBase::validateFramebufferTarget(GLenum target)
{
    if (target == GL_FRAMEBUFFER)
        return true;
    return false;
}

WebGLFramebuffer* WebGLRenderingContextBase::getFramebufferBinding(GLenum target)
{
    if (target == GL_FRAMEBUFFER)
        return m_framebufferBinding.get();
    return nullptr;
}

GLenum WebGLRenderingContextBase::checkFramebufferStatus(GLenum target)
{
    if (isContextLost())
        return GL_FRAMEBUFFER_UNSUPPORTED;
    if (!validateFramebufferTarget(target)) {
        synthesizeGLError(GL_INVALID_ENUM, "checkFramebufferStatus", "invalid target");
        return 0;
    }
    WebGLFramebuffer* framebufferBinding = getFramebufferBinding(target);
    if (!framebufferBinding || !framebufferBinding->object())
        return GL_FRAMEBUFFER_COMPLETE;
    const char* reason = "framebuffer incomplete";
    GLenum result = framebufferBinding->checkStatus(&reason);
    if (result != GL_FRAMEBUFFER_COMPLETE) {
        emitGLWarning("checkFramebufferStatus", reason);
        return result;
    }
    result = webContext()->checkFramebufferStatus(target);
    return result;
}

void WebGLRenderingContextBase::clear(GLbitfield mask)
{
    if (isContextLost())
        return;
    if (mask & ~(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT)) {
        synthesizeGLError(GL_INVALID_VALUE, "clear", "invalid mask");
        return;
    }
    const char* reason = "framebuffer incomplete";
    if (m_framebufferBinding && !m_framebufferBinding->onAccess(webContext(), &reason)) {
        synthesizeGLError(GL_INVALID_FRAMEBUFFER_OPERATION, "clear", reason);
        return;
    }
    if (clearIfComposited(mask) != CombinedClear)
        webContext()->clear(mask);
    markContextChanged(CanvasChanged);
}

void WebGLRenderingContextBase::clearColor(GLfloat r, GLfloat g, GLfloat b, GLfloat a)
{
    if (isContextLost())
        return;
    if (std::isnan(r))
        r = 0;
    if (std::isnan(g))
        g = 0;
    if (std::isnan(b))
        b = 0;
    if (std::isnan(a))
        a = 1;
    m_clearColor[0] = r;
    m_clearColor[1] = g;
    m_clearColor[2] = b;
    m_clearColor[3] = a;
    webContext()->clearColor(r, g, b, a);
}

void WebGLRenderingContextBase::clearDepth(GLfloat depth)
{
    if (isContextLost())
        return;
    m_clearDepth = depth;
    webContext()->clearDepth(depth);
}

void WebGLRenderingContextBase::clearStencil(GLint s)
{
    if (isContextLost())
        return;
    m_clearStencil = s;
    webContext()->clearStencil(s);
}

void WebGLRenderingContextBase::colorMask(GLboolean red, GLboolean green, GLboolean blue, GLboolean alpha)
{
    if (isContextLost())
        return;
    m_colorMask[0] = red;
    m_colorMask[1] = green;
    m_colorMask[2] = blue;
    m_colorMask[3] = alpha;
    webContext()->colorMask(red, green, blue, alpha);
}

void WebGLRenderingContextBase::compileShader(WebGLShader* shader)
{
    if (isContextLost() || !validateWebGLObject("compileShader", shader))
        return;
    webContext()->compileShader(objectOrZero(shader));
}

void WebGLRenderingContextBase::compressedTexImage2D(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, DOMArrayBufferView* data)
{
    if (isContextLost())
        return;
    if (!validateTexFuncLevel("compressedTexImage2D", target, level))
        return;

    if (!validateCompressedTexFormat(internalformat)) {
        synthesizeGLError(GL_INVALID_ENUM, "compressedTexImage2D", "invalid internalformat");
        return;
    }
    if (border) {
        synthesizeGLError(GL_INVALID_VALUE, "compressedTexImage2D", "border not 0");
        return;
    }
    if (!validateCompressedTexDimensions("compressedTexImage2D", NotTexSubImage2D, target, level, width, height, internalformat))
        return;
    if (!validateCompressedTexFuncData("compressedTexImage2D", width, height, internalformat, data))
        return;

    WebGLTexture* tex = validateTextureBinding("compressedTexImage2D", target, true);
    if (!tex)
        return;

    if (tex->isImmutable()) {
        synthesizeGLError(GL_INVALID_OPERATION, "compressedTexImage2D", "attempted to modify immutable texture");
        return;
    }
    if (isNPOTStrict() && level && WebGLTexture::isNPOT(width, height)) {
        synthesizeGLError(GL_INVALID_VALUE, "compressedTexImage2D", "level > 0 not power of 2");
        return;
    }
    webContext()->compressedTexImage2D(target, level, internalformat, width, height,
        border, data->byteLength(), data->baseAddress());
    tex->setLevelInfo(target, level, internalformat, width, height, 1, GL_UNSIGNED_BYTE);
}

void WebGLRenderingContextBase::compressedTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, DOMArrayBufferView* data)
{
    if (isContextLost())
        return;
    if (!validateTexFuncLevel("compressedTexSubImage2D", target, level))
        return;
    if (!validateCompressedTexFormat(format)) {
        synthesizeGLError(GL_INVALID_ENUM, "compressedTexSubImage2D", "invalid format");
        return;
    }
    if (!validateCompressedTexFuncData("compressedTexSubImage2D", width, height, format, data))
        return;

    WebGLTexture* tex = validateTextureBinding("compressedTexSubImage2D", target, true);
    if (!tex)
        return;

    if (!isWebGL2OrHigher() && format != tex->getInternalFormat(target, level)) {
        synthesizeGLError(GL_INVALID_OPERATION, "compressedTexSubImage2D", "format does not match texture format");
        return;
    }

    if (!validateCompressedTexSubDimensions("compressedTexSubImage2D", target, level, xoffset, yoffset, width, height, format, tex))
        return;

    webContext()->compressedTexSubImage2D(target, level, xoffset, yoffset,
        width, height, format, data->byteLength(), data->baseAddress());
}

bool WebGLRenderingContextBase::validateSettableTexFormat(const char* functionName, GLenum format)
{
    if (isWebGL2OrHigher())
        return true;

    if (WebGLImageConversion::getChannelBitsByFormat(format) & WebGLImageConversion::ChannelDepthStencil) {
        synthesizeGLError(GL_INVALID_OPERATION, functionName, "format can not be set, only rendered to");
        return false;
    }
    return true;
}

void WebGLRenderingContextBase::copyTexImage2D(GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width, GLsizei height, GLint border)
{
    if (isContextLost())
        return;
    if (!validateTexFuncLevel("copyTexImage2D", target, level))
        return;
    if (!validateTexFuncParameters("copyTexImage2D", NotTexSubImage2D, target, level, internalformat, width, height, border, internalformat, GL_UNSIGNED_BYTE))
        return;
    if (!validateSettableTexFormat("copyTexImage2D", internalformat))
        return;
    WebGLTexture* tex = validateTextureBinding("copyTexImage2D", target, true);
    if (!tex)
        return;
    if (tex->isImmutable()) {
        synthesizeGLError(GL_INVALID_OPERATION, "copyTexImage2D", "attempted to modify immutable texture");
        return;
    }
    if (!isTexInternalFormatColorBufferCombinationValid(internalformat, boundFramebufferColorFormat())) {
        synthesizeGLError(GL_INVALID_OPERATION, "copyTexImage2D", "framebuffer is incompatible format");
        return;
    }
    if (isNPOTStrict() && level && WebGLTexture::isNPOT(width, height)) {
        synthesizeGLError(GL_INVALID_VALUE, "copyTexImage2D", "level > 0 not power of 2");
        return;
    }
    WebGLFramebuffer* readFramebufferBinding = nullptr;
    if (!validateReadBufferAndGetInfo("copyTexImage2D", readFramebufferBinding, nullptr, nullptr))
        return;
    clearIfComposited();
    ScopedDrawingBufferBinder binder(drawingBuffer(), readFramebufferBinding);
    webContext()->copyTexImage2D(target, level, internalformat, x, y, width, height, border);
    // FIXME: if the framebuffer is not complete, none of the below should be executed.
    tex->setLevelInfo(target, level, internalformat, width, height, 1, GL_UNSIGNED_BYTE);
}

void WebGLRenderingContextBase::copyTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height)
{
    if (isContextLost())
        return;
    if (!validateCopyTexSubImage("copyTexSubImage2D", target, level, xoffset, yoffset, 0, x, y, width, height))
        return;
    WebGLFramebuffer* readFramebufferBinding = nullptr;
    if (!validateReadBufferAndGetInfo("copyTexSubImage2D", readFramebufferBinding, nullptr, nullptr))
        return;
    clearIfComposited();
    ScopedDrawingBufferBinder binder(drawingBuffer(), readFramebufferBinding);
    webContext()->copyTexSubImage2D(target, level, xoffset, yoffset, x, y, width, height);
}

WebGLBuffer* WebGLRenderingContextBase::createBuffer()
{
    if (isContextLost())
        return nullptr;
    WebGLBuffer* o = WebGLBuffer::create(this);
    addSharedObject(o);
    return o;
}

WebGLFramebuffer* WebGLRenderingContextBase::createFramebuffer()
{
    if (isContextLost())
        return nullptr;
    WebGLFramebuffer* o = WebGLFramebuffer::create(this);
    addContextObject(o);
    return o;
}

WebGLTexture* WebGLRenderingContextBase::createTexture()
{
    if (isContextLost())
        return nullptr;
    WebGLTexture* o = WebGLTexture::create(this);
    addSharedObject(o);
    return o;
}

WebGLProgram* WebGLRenderingContextBase::createProgram()
{
    if (isContextLost())
        return nullptr;
    WebGLProgram* o = WebGLProgram::create(this);
    addSharedObject(o);
    return o;
}

WebGLRenderbuffer* WebGLRenderingContextBase::createRenderbuffer()
{
    if (isContextLost())
        return nullptr;
    WebGLRenderbuffer* o = WebGLRenderbuffer::create(this);
    addSharedObject(o);
    return o;
}

WebGLRenderbuffer* WebGLRenderingContextBase::ensureEmulatedStencilBuffer(GLenum target, WebGLRenderbuffer* renderbuffer)
{
    if (isContextLost())
        return nullptr;
    if (!renderbuffer->emulatedStencilBuffer()) {
        renderbuffer->setEmulatedStencilBuffer(createRenderbuffer());
        webContext()->bindRenderbuffer(target, objectOrZero(renderbuffer->emulatedStencilBuffer()));
        webContext()->bindRenderbuffer(target, objectOrZero(m_renderbufferBinding.get()));
    }
    return renderbuffer->emulatedStencilBuffer();
}

WebGLShader* WebGLRenderingContextBase::createShader(GLenum type)
{
    if (isContextLost())
        return nullptr;
    if (type != GL_VERTEX_SHADER && type != GL_FRAGMENT_SHADER) {
        synthesizeGLError(GL_INVALID_ENUM, "createShader", "invalid shader type");
        return nullptr;
    }

    WebGLShader* o = WebGLShader::create(this, type);
    addSharedObject(o);
    return o;
}

void WebGLRenderingContextBase::cullFace(GLenum mode)
{
    if (isContextLost())
        return;
    switch (mode) {
    case GL_FRONT_AND_BACK:
    case GL_FRONT:
    case GL_BACK:
        break;
    default:
        synthesizeGLError(GL_INVALID_ENUM, "cullFace", "invalid mode");
        return;
    }
    webContext()->cullFace(mode);
}

bool WebGLRenderingContextBase::deleteObject(WebGLObject* object)
{
    if (isContextLost() || !object)
        return false;
    if (!object->validate(contextGroup(), this)) {
        synthesizeGLError(GL_INVALID_OPERATION, "delete", "object does not belong to this context");
        return false;
    }
    if (object->hasObject()) {
        // We need to pass in context here because we want
        // things in this context unbound.
        object->deleteObject(webContext());
    }
    return true;
}

void WebGLRenderingContextBase::deleteBuffer(WebGLBuffer* buffer)
{
    if (!deleteObject(buffer))
        return;
    removeBoundBuffer(buffer);
}

void WebGLRenderingContextBase::deleteFramebuffer(WebGLFramebuffer* framebuffer)
{
    if (!deleteObject(framebuffer))
        return;
    if (framebuffer == m_framebufferBinding) {
        m_framebufferBinding = nullptr;
        drawingBuffer()->setFramebufferBinding(GL_FRAMEBUFFER, 0);
        // Have to call drawingBuffer()->bind() here to bind back to internal fbo.
        drawingBuffer()->bind(GL_FRAMEBUFFER);
    }
}

void WebGLRenderingContextBase::deleteProgram(WebGLProgram* program)
{
    deleteObject(program);
    // We don't reset m_currentProgram to 0 here because the deletion of the
    // current program is delayed.
}

void WebGLRenderingContextBase::deleteRenderbuffer(WebGLRenderbuffer* renderbuffer)
{
    if (!deleteObject(renderbuffer))
        return;
    if (renderbuffer == m_renderbufferBinding)
        m_renderbufferBinding = nullptr;
    if (m_framebufferBinding)
        m_framebufferBinding->removeAttachmentFromBoundFramebuffer(GL_FRAMEBUFFER, renderbuffer);
    if (getFramebufferBinding(GL_READ_FRAMEBUFFER))
        getFramebufferBinding(GL_READ_FRAMEBUFFER)->removeAttachmentFromBoundFramebuffer(GL_READ_FRAMEBUFFER, renderbuffer);
}

void WebGLRenderingContextBase::deleteShader(WebGLShader* shader)
{
    deleteObject(shader);
}

void WebGLRenderingContextBase::deleteTexture(WebGLTexture* texture)
{
    if (!deleteObject(texture))
        return;

    int maxBoundTextureIndex = -1;
    for (size_t i = 0; i < m_onePlusMaxNonDefaultTextureUnit; ++i) {
        if (texture == m_textureUnits[i].m_texture2DBinding) {
            m_textureUnits[i].m_texture2DBinding = nullptr;
            maxBoundTextureIndex = i;
            if (!i)
                drawingBuffer()->setTexture2DBinding(0);
        }
        if (texture == m_textureUnits[i].m_textureCubeMapBinding) {
            m_textureUnits[i].m_textureCubeMapBinding = nullptr;
            maxBoundTextureIndex = i;
        }
        if (isWebGL2OrHigher()) {
            if (texture == m_textureUnits[i].m_texture3DBinding) {
                m_textureUnits[i].m_texture3DBinding = nullptr;
                maxBoundTextureIndex = i;
            }
            if (texture == m_textureUnits[i].m_texture2DArrayBinding) {
                m_textureUnits[i].m_texture2DArrayBinding = nullptr;
                maxBoundTextureIndex = i;
            }
        }
    }
    if (m_framebufferBinding)
        m_framebufferBinding->removeAttachmentFromBoundFramebuffer(GL_FRAMEBUFFER, texture);
    if (getFramebufferBinding(GL_READ_FRAMEBUFFER))
        getFramebufferBinding(GL_READ_FRAMEBUFFER)->removeAttachmentFromBoundFramebuffer(GL_READ_FRAMEBUFFER, texture);

    // If the deleted was bound to the the current maximum index, trace backwards to find the new max texture index
    if (m_onePlusMaxNonDefaultTextureUnit == static_cast<unsigned long>(maxBoundTextureIndex + 1)) {
        findNewMaxNonDefaultTextureUnit();
    }
}

void WebGLRenderingContextBase::depthFunc(GLenum func)
{
    if (isContextLost())
        return;
    if (!validateStencilOrDepthFunc("depthFunc", func))
        return;
    webContext()->depthFunc(func);
}

void WebGLRenderingContextBase::depthMask(GLboolean flag)
{
    if (isContextLost())
        return;
    m_depthMask = flag;
    webContext()->depthMask(flag);
}

void WebGLRenderingContextBase::depthRange(GLfloat zNear, GLfloat zFar)
{
    if (isContextLost())
        return;
    if (zNear > zFar) {
        synthesizeGLError(GL_INVALID_OPERATION, "depthRange", "zNear > zFar");
        return;
    }
    webContext()->depthRange(zNear, zFar);
}

void WebGLRenderingContextBase::detachShader(WebGLProgram* program, WebGLShader* shader)
{
    if (isContextLost() || !validateWebGLObject("detachShader", program) || !validateWebGLObject("detachShader", shader))
        return;
    if (!program->detachShader(shader)) {
        synthesizeGLError(GL_INVALID_OPERATION, "detachShader", "shader not attached");
        return;
    }
    webContext()->detachShader(objectOrZero(program), objectOrZero(shader));
    shader->onDetached(webContext());
}

void WebGLRenderingContextBase::disable(GLenum cap)
{
    if (isContextLost() || !validateCapability("disable", cap))
        return;
    if (cap == GL_STENCIL_TEST) {
        m_stencilEnabled = false;
        applyStencilTest();
        return;
    }
    if (cap == GL_SCISSOR_TEST) {
        m_scissorEnabled = false;
        drawingBuffer()->setScissorEnabled(m_scissorEnabled);
    }
    webContext()->disable(cap);
}

void WebGLRenderingContextBase::disableVertexAttribArray(GLuint index)
{
    if (isContextLost())
        return;
    if (index >= m_maxVertexAttribs) {
        synthesizeGLError(GL_INVALID_VALUE, "disableVertexAttribArray", "index out of range");
        return;
    }

    WebGLVertexArrayObjectBase::VertexAttribState* state = m_boundVertexArrayObject->getVertexAttribState(index);
    state->enabled = false;

    webContext()->disableVertexAttribArray(index);
}

bool WebGLRenderingContextBase::validateRenderingState(const char* functionName)
{
    if (!m_currentProgram) {
        synthesizeGLError(GL_INVALID_OPERATION, functionName, "no valid shader program in use");
        return false;
    }

    return true;
}

bool WebGLRenderingContextBase::validateWebGLObject(const char* functionName, WebGLObject* object)
{
    if (!object || !object->hasObject()) {
        synthesizeGLError(GL_INVALID_VALUE, functionName, "no object or object deleted");
        return false;
    }
    if (!object->validate(contextGroup(), this)) {
        synthesizeGLError(GL_INVALID_OPERATION, functionName, "object does not belong to this context");
        return false;
    }
    return true;
}

void WebGLRenderingContextBase::drawArrays(GLenum mode, GLint first, GLsizei count)
{
    if (!validateDrawArrays("drawArrays", mode, first, count))
        return;

    clearIfComposited();

    handleTextureCompleteness("drawArrays", true);
    webContext()->drawArrays(mode, first, count);
    handleTextureCompleteness("drawArrays", false);
    markContextChanged(CanvasChanged);
}

void WebGLRenderingContextBase::drawElements(GLenum mode, GLsizei count, GLenum type, long long offset)
{
    if (!validateDrawElements("drawElements", mode, count, type, offset))
        return;

    clearIfComposited();

    handleTextureCompleteness("drawElements", true);
    webContext()->drawElements(mode, count, type, static_cast<GLintptr>(offset));
    handleTextureCompleteness("drawElements", false);
    markContextChanged(CanvasChanged);
}

void WebGLRenderingContextBase::drawArraysInstancedANGLE(GLenum mode, GLint first, GLsizei count, GLsizei primcount)
{
    if (!validateDrawArrays("drawArraysInstancedANGLE", mode, first, count))
        return;

    if (!validateDrawInstanced("drawArraysInstancedANGLE", primcount))
        return;

    clearIfComposited();

    handleTextureCompleteness("drawArraysInstancedANGLE", true);
    webContext()->drawArraysInstancedANGLE(mode, first, count, primcount);
    handleTextureCompleteness("drawArraysInstancedANGLE", false);
    markContextChanged(CanvasChanged);
}

void WebGLRenderingContextBase::drawElementsInstancedANGLE(GLenum mode, GLsizei count, GLenum type, long long offset, GLsizei primcount)
{
    if (!validateDrawElements("drawElementsInstancedANGLE", mode, count, type, offset))
        return;

    if (!validateDrawInstanced("drawElementsInstancedANGLE", primcount))
        return;

    clearIfComposited();

    handleTextureCompleteness("drawElementsInstancedANGLE", true);
    webContext()->drawElementsInstancedANGLE(mode, count, type, static_cast<GLintptr>(offset), primcount);
    handleTextureCompleteness("drawElementsInstancedANGLE", false);
    markContextChanged(CanvasChanged);
}

void WebGLRenderingContextBase::enable(GLenum cap)
{
    if (isContextLost() || !validateCapability("enable", cap))
        return;
    if (cap == GL_STENCIL_TEST) {
        m_stencilEnabled = true;
        applyStencilTest();
        return;
    }
    if (cap == GL_SCISSOR_TEST) {
        m_scissorEnabled = true;
        drawingBuffer()->setScissorEnabled(m_scissorEnabled);
    }
    webContext()->enable(cap);
}

void WebGLRenderingContextBase::enableVertexAttribArray(GLuint index)
{
    if (isContextLost())
        return;
    if (index >= m_maxVertexAttribs) {
        synthesizeGLError(GL_INVALID_VALUE, "enableVertexAttribArray", "index out of range");
        return;
    }

    WebGLVertexArrayObjectBase::VertexAttribState* state = m_boundVertexArrayObject->getVertexAttribState(index);
    state->enabled = true;

    webContext()->enableVertexAttribArray(index);
}

void WebGLRenderingContextBase::finish()
{
    if (isContextLost())
        return;
    webContext()->flush(); // Intentionally a flush, not a finish.
}

void WebGLRenderingContextBase::flush()
{
    if (isContextLost())
        return;
    webContext()->flush();
}

void WebGLRenderingContextBase::framebufferRenderbuffer(GLenum target, GLenum attachment, GLenum renderbuffertarget, WebGLRenderbuffer* buffer)
{
    if (isContextLost() || !validateFramebufferFuncParameters("framebufferRenderbuffer", target, attachment))
        return;
    if (renderbuffertarget != GL_RENDERBUFFER) {
        synthesizeGLError(GL_INVALID_ENUM, "framebufferRenderbuffer", "invalid target");
        return;
    }
    if (buffer && !buffer->validate(contextGroup(), this)) {
        synthesizeGLError(GL_INVALID_OPERATION, "framebufferRenderbuffer", "no buffer or buffer not from this context");
        return;
    }
    // Don't allow the default framebuffer to be mutated; all current
    // implementations use an FBO internally in place of the default
    // FBO.
    WebGLFramebuffer* framebufferBinding = getFramebufferBinding(target);
    if (!framebufferBinding || !framebufferBinding->object()) {
        synthesizeGLError(GL_INVALID_OPERATION, "framebufferRenderbuffer", "no framebuffer bound");
        return;
    }
    Platform3DObject bufferObject = objectOrZero(buffer);
    switch (attachment) {
    case GL_DEPTH_STENCIL_ATTACHMENT:
        if (isWebGL2OrHigher() || isDepthStencilSupported() || !buffer) {
            webContext()->framebufferRenderbuffer(target, GL_DEPTH_ATTACHMENT, renderbuffertarget, bufferObject);
            webContext()->framebufferRenderbuffer(target, GL_STENCIL_ATTACHMENT, renderbuffertarget, bufferObject);
        } else {
            WebGLRenderbuffer* emulatedStencilBuffer = ensureEmulatedStencilBuffer(renderbuffertarget, buffer);
            if (!emulatedStencilBuffer) {
                synthesizeGLError(GL_OUT_OF_MEMORY, "framebufferRenderbuffer", "out of memory");
                return;
            }
            webContext()->framebufferRenderbuffer(target, GL_DEPTH_ATTACHMENT, renderbuffertarget, bufferObject);
            webContext()->framebufferRenderbuffer(target, GL_STENCIL_ATTACHMENT, renderbuffertarget, objectOrZero(emulatedStencilBuffer));
        }
        break;
    default:
        webContext()->framebufferRenderbuffer(target, attachment, renderbuffertarget, bufferObject);
    }
    if (isWebGL2OrHigher() && attachment == GL_DEPTH_STENCIL_ATTACHMENT) {
        // On ES3, DEPTH_STENCIL_ATTACHMENT is like an alias for DEPTH_ATTACHMENT + STENCIL_ATTACHMENT.
        // We divide it here so in WebGLFramebuffer, we don't have to handle DEPTH_STENCIL_ATTACHMENT in WebGL 2.
        framebufferBinding->setAttachmentForBoundFramebuffer(target, GL_DEPTH_ATTACHMENT, buffer);
        framebufferBinding->setAttachmentForBoundFramebuffer(target, GL_STENCIL_ATTACHMENT, buffer);
    } else {
        framebufferBinding->setAttachmentForBoundFramebuffer(target, attachment, buffer);
    }
    applyStencilTest();
}

void WebGLRenderingContextBase::framebufferTexture2D(GLenum target, GLenum attachment, GLenum textarget, WebGLTexture* texture, GLint level)
{
    if (isContextLost() || !validateFramebufferFuncParameters("framebufferTexture2D", target, attachment))
        return;
    if (isWebGL2OrHigher()) {
        if (!validateTexFuncLevel("framebufferTexture2D", textarget, level))
            return;
    } else if (level) {
        synthesizeGLError(GL_INVALID_VALUE, "framebufferTexture2D", "level not 0");
        return;
    }
    if (texture && !texture->validate(contextGroup(), this)) {
        synthesizeGLError(GL_INVALID_OPERATION, "framebufferTexture2D", "no texture or texture not from this context");
        return;
    }
    // Don't allow the default framebuffer to be mutated; all current
    // implementations use an FBO internally in place of the default
    // FBO.
    WebGLFramebuffer* framebufferBinding = getFramebufferBinding(target);
    if (!framebufferBinding || !framebufferBinding->object()) {
        synthesizeGLError(GL_INVALID_OPERATION, "framebufferTexture2D", "no framebuffer bound");
        return;
    }
    Platform3DObject textureObject = objectOrZero(texture);
    switch (attachment) {
    case GL_DEPTH_STENCIL_ATTACHMENT:
        webContext()->framebufferTexture2D(target, GL_DEPTH_ATTACHMENT, textarget, textureObject, level);
        webContext()->framebufferTexture2D(target, GL_STENCIL_ATTACHMENT, textarget, textureObject, level);
        break;
    case GL_DEPTH_ATTACHMENT:
        webContext()->framebufferTexture2D(target, attachment, textarget, textureObject, level);
        break;
    case GL_STENCIL_ATTACHMENT:
        webContext()->framebufferTexture2D(target, attachment, textarget, textureObject, level);
        break;
    default:
        webContext()->framebufferTexture2D(target, attachment, textarget, textureObject, level);
    }
    framebufferBinding->setAttachmentForBoundFramebuffer(target, attachment, textarget, texture, level);
    applyStencilTest();
}

void WebGLRenderingContextBase::frontFace(GLenum mode)
{
    if (isContextLost())
        return;
    switch (mode) {
    case GL_CW:
    case GL_CCW:
        break;
    default:
        synthesizeGLError(GL_INVALID_ENUM, "frontFace", "invalid mode");
        return;
    }
    webContext()->frontFace(mode);
}

void WebGLRenderingContextBase::generateMipmap(GLenum target)
{
    if (isContextLost())
        return;
    WebGLTexture* tex = validateTextureBinding("generateMipmap", target, false);
    if (!tex)
        return;
    if (!tex->canGenerateMipmaps()) {
        synthesizeGLError(GL_INVALID_OPERATION, "generateMipmap", "cannot generate mipmaps");
        return;
    }
    if (tex->getInternalFormat(target, 0) == GL_SRGB_EXT || tex->getInternalFormat(target, 0) == GL_SRGB_ALPHA_EXT) {
        synthesizeGLError(GL_INVALID_OPERATION, "generateMipmap", "cannot generate mipmaps for sRGB textures");
        return;
    }
    if (!validateSettableTexFormat("generateMipmap", tex->getInternalFormat(target, 0)))
        return;

    // generateMipmap won't work properly if minFilter is not NEAREST_MIPMAP_LINEAR
    // on Mac.  Remove the hack once this driver bug is fixed.
#if OS(MACOSX)
    bool needToResetMinFilter = false;
    if (tex->getMinFilter() != GL_NEAREST_MIPMAP_LINEAR) {
        webContext()->texParameteri(target, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);
        needToResetMinFilter = true;
    }
#endif
    webContext()->generateMipmap(target);
#if OS(MACOSX)
    if (needToResetMinFilter)
        webContext()->texParameteri(target, GL_TEXTURE_MIN_FILTER, tex->getMinFilter());
#endif
    tex->generateMipmapLevelInfo();
}

WebGLActiveInfo* WebGLRenderingContextBase::getActiveAttrib(WebGLProgram* program, GLuint index)
{
    if (isContextLost() || !validateWebGLObject("getActiveAttrib", program))
        return nullptr;
    WebGraphicsContext3D::ActiveInfo info;
    if (!webContext()->getActiveAttrib(objectOrZero(program), index, info))
        return nullptr;
    return WebGLActiveInfo::create(info.name, info.type, info.size);
}

WebGLActiveInfo* WebGLRenderingContextBase::getActiveUniform(WebGLProgram* program, GLuint index)
{
    if (isContextLost() || !validateWebGLObject("getActiveUniform", program))
        return nullptr;
    WebGraphicsContext3D::ActiveInfo info;
    if (!webContext()->getActiveUniform(objectOrZero(program), index, info))
        return nullptr;
    return WebGLActiveInfo::create(info.name, info.type, info.size);
}

Nullable<HeapVector<Member<WebGLShader>>> WebGLRenderingContextBase::getAttachedShaders(WebGLProgram* program)
{
    if (isContextLost() || !validateWebGLObject("getAttachedShaders", program))
        return nullptr;

    HeapVector<Member<WebGLShader>> shaderObjects;
    const GLenum shaderType[] = {
        GL_VERTEX_SHADER,
        GL_FRAGMENT_SHADER
    };
    for (unsigned i = 0; i < sizeof(shaderType) / sizeof(GLenum); ++i) {
        WebGLShader* shader = program->getAttachedShader(shaderType[i]);
        if (shader)
            shaderObjects.append(shader);
    }
    return shaderObjects;
}

GLint WebGLRenderingContextBase::getAttribLocation(WebGLProgram* program, const String& name)
{
    if (isContextLost() || !validateWebGLObject("getAttribLocation", program))
        return -1;
    if (!validateLocationLength("getAttribLocation", name))
        return -1;
    if (!validateString("getAttribLocation", name))
        return -1;
    if (isPrefixReserved(name))
        return -1;
    if (!program->linkStatus()) {
        synthesizeGLError(GL_INVALID_OPERATION, "getAttribLocation", "program not linked");
        return 0;
    }
    return webContext()->getAttribLocation(objectOrZero(program), name.utf8().data());
}

bool WebGLRenderingContextBase::validateBufferTarget(const char* functionName, GLenum target)
{
    switch (target) {
    case GL_ARRAY_BUFFER:
    case GL_ELEMENT_ARRAY_BUFFER:
        return true;
    default:
        synthesizeGLError(GL_INVALID_ENUM, functionName, "invalid target");
        return false;
    }
}

ScriptValue WebGLRenderingContextBase::getBufferParameter(ScriptState* scriptState, GLenum target, GLenum pname)
{
    if (isContextLost() || !validateBufferTarget("getBufferParameter", target))
        return ScriptValue::createNull(scriptState);

    switch (pname) {
    case GL_BUFFER_USAGE:
        {
            GLint value = 0;
            webContext()->getBufferParameteriv(target, pname, &value);
            return WebGLAny(scriptState, static_cast<unsigned>(value));
        }
    case GL_BUFFER_SIZE:
        {
            GLint value = 0;
            webContext()->getBufferParameteriv(target, pname, &value);
            if (!isWebGL2OrHigher())
                return WebGLAny(scriptState, value);
            return WebGLAny(scriptState, static_cast<GLint64>(value));
        }
    default:
        synthesizeGLError(GL_INVALID_ENUM, "getBufferParameter", "invalid parameter name");
        return ScriptValue::createNull(scriptState);
    }
}

void WebGLRenderingContextBase::getContextAttributes(Nullable<WebGLContextAttributes>& result)
{
    if (isContextLost())
        return;
    result.set(m_requestedAttributes);
    // Some requested attributes may not be honored, so we need to query the underlying
    // context/drawing buffer and adjust accordingly.
    WebGraphicsContext3D::Attributes attrs = drawingBuffer()->getActualAttributes();
    if (m_requestedAttributes.depth() && !attrs.depth)
        result.get().setDepth(false);
    if (m_requestedAttributes.stencil() && !attrs.stencil)
        result.get().setStencil(false);
    result.get().setAntialias(drawingBuffer()->multisample());
}

GLenum WebGLRenderingContextBase::getError()
{
    if (m_lostContextErrors.size()) {
        GLenum err = m_lostContextErrors.first();
        m_lostContextErrors.remove(0);
        return err;
    }

    if (isContextLost())
        return GL_NO_ERROR;

    return webContext()->getError();
}

const char* const* WebGLRenderingContextBase::ExtensionTracker::prefixes() const
{
    static const char* const unprefixed[] = { "", 0, };
    return m_prefixes ? m_prefixes : unprefixed;
}

bool WebGLRenderingContextBase::ExtensionTracker::matchesNameWithPrefixes(const String& name) const
{
    const char* const* prefixSet = prefixes();
    for (; *prefixSet; ++prefixSet) {
        String prefixedName = String(*prefixSet) + extensionName();
        if (equalIgnoringCase(prefixedName, name)) {
            return true;
        }
    }
    return false;
}

bool WebGLRenderingContextBase::extensionSupportedAndAllowed(const ExtensionTracker* tracker)
{
    if (tracker->draft() && !RuntimeEnabledFeatures::webGLDraftExtensionsEnabled())
        return false;
    if (!tracker->supported(this))
        return false;
    return true;
}

ScriptValue WebGLRenderingContextBase::getExtension(ScriptState* scriptState, const String& name)
{
    WebGLExtension* extension = nullptr;

    if (!isContextLost()) {
        for (size_t i = 0; i < m_extensions.size(); ++i) {
            ExtensionTracker* tracker = m_extensions[i];
            if (tracker->matchesNameWithPrefixes(name)) {
                if (extensionSupportedAndAllowed(tracker)) {
                    extension = tracker->getExtension(this);
                    if (extension)
                        m_extensionEnabled[extension->name()] = true;
                }
                break;
            }
        }
    }

    return ScriptValue(scriptState, toV8(extension, scriptState->context()->Global(), scriptState->isolate()));
}

ScriptValue WebGLRenderingContextBase::getFramebufferAttachmentParameter(ScriptState* scriptState, GLenum target, GLenum attachment, GLenum pname)
{
    if (isContextLost() || !validateFramebufferFuncParameters("getFramebufferAttachmentParameter", target, attachment))
        return ScriptValue::createNull(scriptState);

    if (!m_framebufferBinding || !m_framebufferBinding->object()) {
        synthesizeGLError(GL_INVALID_OPERATION, "getFramebufferAttachmentParameter", "no framebuffer bound");
        return ScriptValue::createNull(scriptState);
    }

    WebGLSharedObject* attachmentObject = m_framebufferBinding->getAttachmentObject(attachment);
    if (!attachmentObject) {
        if (pname == GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE)
            return WebGLAny(scriptState, GL_NONE);
        // OpenGL ES 2.0 specifies INVALID_ENUM in this case, while desktop GL
        // specifies INVALID_OPERATION.
        synthesizeGLError(GL_INVALID_ENUM, "getFramebufferAttachmentParameter", "invalid parameter name");
        return ScriptValue::createNull(scriptState);
    }

    ASSERT(attachmentObject->isTexture() || attachmentObject->isRenderbuffer());
    if (attachmentObject->isTexture()) {
        switch (pname) {
        case GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE:
            return WebGLAny(scriptState, GL_TEXTURE);
        case GL_FRAMEBUFFER_ATTACHMENT_OBJECT_NAME:
            return WebGLAny(scriptState, attachmentObject);
        case GL_FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL:
        case GL_FRAMEBUFFER_ATTACHMENT_TEXTURE_CUBE_MAP_FACE:
            {
                GLint value = 0;
                webContext()->getFramebufferAttachmentParameteriv(target, attachment, pname, &value);
                return WebGLAny(scriptState, value);
            }
        case GL_FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING_EXT:
            if (extensionEnabled(EXTsRGBName)) {
                GLint value = 0;
                webContext()->getFramebufferAttachmentParameteriv(target, attachment, pname, &value);
                return WebGLAny(scriptState, static_cast<unsigned>(value));
            }
            synthesizeGLError(GL_INVALID_ENUM, "getFramebufferAttachmentParameter", "invalid parameter name for renderbuffer attachment");
            return ScriptValue::createNull(scriptState);
        default:
            synthesizeGLError(GL_INVALID_ENUM, "getFramebufferAttachmentParameter", "invalid parameter name for texture attachment");
            return ScriptValue::createNull(scriptState);
        }
    } else {
        switch (pname) {
        case GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE:
            return WebGLAny(scriptState, GL_RENDERBUFFER);
        case GL_FRAMEBUFFER_ATTACHMENT_OBJECT_NAME:
            return WebGLAny(scriptState, attachmentObject);
        case GL_FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING_EXT:
            if (extensionEnabled(EXTsRGBName)) {
                GLint value = 0;
                webContext()->getFramebufferAttachmentParameteriv(target, attachment, pname, &value);
                return WebGLAny(scriptState, value);
            }
            synthesizeGLError(GL_INVALID_ENUM, "getFramebufferAttachmentParameter", "invalid parameter name for renderbuffer attachment");
            return ScriptValue::createNull(scriptState);
        default:
            synthesizeGLError(GL_INVALID_ENUM, "getFramebufferAttachmentParameter", "invalid parameter name for renderbuffer attachment");
            return ScriptValue::createNull(scriptState);
        }
    }
}

ScriptValue WebGLRenderingContextBase::getParameter(ScriptState* scriptState, GLenum pname)
{
    if (isContextLost())
        return ScriptValue::createNull(scriptState);
    const int intZero = 0;
    switch (pname) {
    case GL_ACTIVE_TEXTURE:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_ALIASED_LINE_WIDTH_RANGE:
        return getWebGLFloatArrayParameter(scriptState, pname);
    case GL_ALIASED_POINT_SIZE_RANGE:
        return getWebGLFloatArrayParameter(scriptState, pname);
    case GL_ALPHA_BITS:
        return getIntParameter(scriptState, pname);
    case GL_ARRAY_BUFFER_BINDING:
        return WebGLAny(scriptState, m_boundArrayBuffer.get());
    case GL_BLEND:
        return getBooleanParameter(scriptState, pname);
    case GL_BLEND_COLOR:
        return getWebGLFloatArrayParameter(scriptState, pname);
    case GL_BLEND_DST_ALPHA:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_BLEND_DST_RGB:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_BLEND_EQUATION_ALPHA:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_BLEND_EQUATION_RGB:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_BLEND_SRC_ALPHA:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_BLEND_SRC_RGB:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_BLUE_BITS:
        return getIntParameter(scriptState, pname);
    case GL_COLOR_CLEAR_VALUE:
        return getWebGLFloatArrayParameter(scriptState, pname);
    case GL_COLOR_WRITEMASK:
        return getBooleanArrayParameter(scriptState, pname);
    case GL_COMPRESSED_TEXTURE_FORMATS:
        return WebGLAny(scriptState, DOMUint32Array::create(m_compressedTextureFormats.data(), m_compressedTextureFormats.size()));
    case GL_CULL_FACE:
        return getBooleanParameter(scriptState, pname);
    case GL_CULL_FACE_MODE:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_CURRENT_PROGRAM:
        return WebGLAny(scriptState, m_currentProgram.get());
    case GL_DEPTH_BITS:
        if (!m_framebufferBinding && !m_requestedAttributes.depth())
            return WebGLAny(scriptState, intZero);
        return getIntParameter(scriptState, pname);
    case GL_DEPTH_CLEAR_VALUE:
        return getFloatParameter(scriptState, pname);
    case GL_DEPTH_FUNC:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_DEPTH_RANGE:
        return getWebGLFloatArrayParameter(scriptState, pname);
    case GL_DEPTH_TEST:
        return getBooleanParameter(scriptState, pname);
    case GL_DEPTH_WRITEMASK:
        return getBooleanParameter(scriptState, pname);
    case GL_DITHER:
        return getBooleanParameter(scriptState, pname);
    case GL_ELEMENT_ARRAY_BUFFER_BINDING:
        return WebGLAny(scriptState, m_boundVertexArrayObject->boundElementArrayBuffer());
    case GL_FRAMEBUFFER_BINDING:
        return WebGLAny(scriptState, m_framebufferBinding.get());
    case GL_FRONT_FACE:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_GENERATE_MIPMAP_HINT:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_GREEN_BITS:
        return getIntParameter(scriptState, pname);
    case GL_IMPLEMENTATION_COLOR_READ_FORMAT:
        return getIntParameter(scriptState, pname);
    case GL_IMPLEMENTATION_COLOR_READ_TYPE:
        return getIntParameter(scriptState, pname);
    case GL_LINE_WIDTH:
        return getFloatParameter(scriptState, pname);
    case GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_CUBE_MAP_TEXTURE_SIZE:
        return getIntParameter(scriptState, pname);
    case GL_MAX_FRAGMENT_UNIFORM_VECTORS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_RENDERBUFFER_SIZE:
        return getIntParameter(scriptState, pname);
    case GL_MAX_TEXTURE_IMAGE_UNITS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_TEXTURE_SIZE:
        return getIntParameter(scriptState, pname);
    case GL_MAX_VARYING_VECTORS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_VERTEX_ATTRIBS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_VERTEX_UNIFORM_VECTORS:
        return getIntParameter(scriptState, pname);
    case GL_MAX_VIEWPORT_DIMS:
        return getWebGLIntArrayParameter(scriptState, pname);
    case GL_NUM_SHADER_BINARY_FORMATS:
        // FIXME: should we always return 0 for this?
        return getIntParameter(scriptState, pname);
    case GL_PACK_ALIGNMENT:
        return getIntParameter(scriptState, pname);
    case GL_POLYGON_OFFSET_FACTOR:
        return getFloatParameter(scriptState, pname);
    case GL_POLYGON_OFFSET_FILL:
        return getBooleanParameter(scriptState, pname);
    case GL_POLYGON_OFFSET_UNITS:
        return getFloatParameter(scriptState, pname);
    case GL_RED_BITS:
        return getIntParameter(scriptState, pname);
    case GL_RENDERBUFFER_BINDING:
        return WebGLAny(scriptState, m_renderbufferBinding.get());
    case GL_RENDERER:
        return WebGLAny(scriptState, String("WebKit WebGL"));
    case GL_SAMPLE_BUFFERS:
        return getIntParameter(scriptState, pname);
    case GL_SAMPLE_COVERAGE_INVERT:
        return getBooleanParameter(scriptState, pname);
    case GL_SAMPLE_COVERAGE_VALUE:
        return getFloatParameter(scriptState, pname);
    case GL_SAMPLES:
        return getIntParameter(scriptState, pname);
    case GL_SCISSOR_BOX:
        return getWebGLIntArrayParameter(scriptState, pname);
    case GL_SCISSOR_TEST:
        return getBooleanParameter(scriptState, pname);
    case GL_SHADING_LANGUAGE_VERSION:
        return WebGLAny(scriptState, "WebGL GLSL ES 1.0 (" + String(webContext()->getString(GL_SHADING_LANGUAGE_VERSION)) + ")");
    case GL_STENCIL_BACK_FAIL:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_BACK_FUNC:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_BACK_PASS_DEPTH_FAIL:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_BACK_PASS_DEPTH_PASS:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_BACK_REF:
        return getIntParameter(scriptState, pname);
    case GL_STENCIL_BACK_VALUE_MASK:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_BACK_WRITEMASK:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_BITS:
        if (!m_framebufferBinding && !m_requestedAttributes.stencil())
            return WebGLAny(scriptState, intZero);
        return getIntParameter(scriptState, pname);
    case GL_STENCIL_CLEAR_VALUE:
        return getIntParameter(scriptState, pname);
    case GL_STENCIL_FAIL:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_FUNC:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_PASS_DEPTH_FAIL:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_PASS_DEPTH_PASS:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_REF:
        return getIntParameter(scriptState, pname);
    case GL_STENCIL_TEST:
        return getBooleanParameter(scriptState, pname);
    case GL_STENCIL_VALUE_MASK:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_STENCIL_WRITEMASK:
        return getUnsignedIntParameter(scriptState, pname);
    case GL_SUBPIXEL_BITS:
        return getIntParameter(scriptState, pname);
    case GL_TEXTURE_BINDING_2D:
        return WebGLAny(scriptState, m_textureUnits[m_activeTextureUnit].m_texture2DBinding.get());
    case GL_TEXTURE_BINDING_CUBE_MAP:
        return WebGLAny(scriptState, m_textureUnits[m_activeTextureUnit].m_textureCubeMapBinding.get());
    case GL_UNPACK_ALIGNMENT:
        return getIntParameter(scriptState, pname);
    case GC3D_UNPACK_FLIP_Y_WEBGL:
        return WebGLAny(scriptState, m_unpackFlipY);
    case GC3D_UNPACK_PREMULTIPLY_ALPHA_WEBGL:
        return WebGLAny(scriptState, m_unpackPremultiplyAlpha);
    case GC3D_UNPACK_COLORSPACE_CONVERSION_WEBGL:
        return WebGLAny(scriptState, m_unpackColorspaceConversion);
    case GL_VENDOR:
        return WebGLAny(scriptState, String("WebKit"));
    case GL_VERSION:
        return WebGLAny(scriptState, "WebGL 1.0 (" + String(webContext()->getString(GL_VERSION)) + ")");
    case GL_VIEWPORT:
        return getWebGLIntArrayParameter(scriptState, pname);
    case GL_FRAGMENT_SHADER_DERIVATIVE_HINT_OES: // OES_standard_derivatives
        if (extensionEnabled(OESStandardDerivativesName) || isWebGL2OrHigher())
            return getUnsignedIntParameter(scriptState, GL_FRAGMENT_SHADER_DERIVATIVE_HINT_OES);
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, OES_standard_derivatives not enabled");
        return ScriptValue::createNull(scriptState);
    case WebGLDebugRendererInfo::UNMASKED_RENDERER_WEBGL:
        if (extensionEnabled(WebGLDebugRendererInfoName))
            return WebGLAny(scriptState, webContext()->getString(GL_RENDERER));
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, WEBGL_debug_renderer_info not enabled");
        return ScriptValue::createNull(scriptState);
    case WebGLDebugRendererInfo::UNMASKED_VENDOR_WEBGL:
        if (extensionEnabled(WebGLDebugRendererInfoName))
            return WebGLAny(scriptState, webContext()->getString(GL_VENDOR));
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, WEBGL_debug_renderer_info not enabled");
        return ScriptValue::createNull(scriptState);
    case GL_VERTEX_ARRAY_BINDING_OES: // OES_vertex_array_object
        if (extensionEnabled(OESVertexArrayObjectName) || isWebGL2OrHigher()) {
            if (!m_boundVertexArrayObject->isDefaultObject())
                return WebGLAny(scriptState, m_boundVertexArrayObject.get());
            return ScriptValue::createNull(scriptState);
        }
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, OES_vertex_array_object not enabled");
        return ScriptValue::createNull(scriptState);
    case GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT: // EXT_texture_filter_anisotropic
        if (extensionEnabled(EXTTextureFilterAnisotropicName))
            return getUnsignedIntParameter(scriptState, GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT);
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, EXT_texture_filter_anisotropic not enabled");
        return ScriptValue::createNull(scriptState);
    case GL_MAX_COLOR_ATTACHMENTS_EXT: // EXT_draw_buffers BEGIN
        if (extensionEnabled(WebGLDrawBuffersName) || isWebGL2OrHigher())
            return WebGLAny(scriptState, maxColorAttachments());
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, WEBGL_draw_buffers not enabled");
        return ScriptValue::createNull(scriptState);
    case GL_MAX_DRAW_BUFFERS_EXT:
        if (extensionEnabled(WebGLDrawBuffersName) || isWebGL2OrHigher())
            return WebGLAny(scriptState, maxDrawBuffers());
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, WEBGL_draw_buffers not enabled");
        return ScriptValue::createNull(scriptState);
    case GL_TIMESTAMP_EXT:
        if (extensionEnabled(EXTDisjointTimerQueryName))
            return getInt64Parameter(scriptState, GL_TIMESTAMP_EXT);
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, EXT_disjoint_timer_query not enabled");
        return ScriptValue::createNull(scriptState);
    case GL_GPU_DISJOINT_EXT:
        if (extensionEnabled(EXTDisjointTimerQueryName))
            return getBooleanParameter(scriptState, GL_GPU_DISJOINT_EXT);
        synthesizeGLError(GL_INVALID_ENUM, "getParameter", "invalid parameter name, EXT_disjoint_timer_query not enabled");
        return ScriptValue::createNull(scriptState);

    default:
        if ((extensionEnabled(WebGLDrawBuffersName) || isWebGL2OrHigher())
            && pname >= GL_DRAW_BUFFER0_EXT
            && pname < static_cast<GLenum>(GL_DRAW_BUFFER0_EXT + maxDrawBuffers