third_party/WebKit/Source/platform/graphics/Gradient.cpp

/*
 * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
 * Copyright (C) 2007 Alp Toker <alp@atoker.com>
 * Copyright (C) 2013 Google 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 "platform/graphics/Gradient.h"

#include "platform/geometry/FloatRect.h"
#include "platform/graphics/GraphicsContext.h"
#include "platform/graphics/skia/SkiaUtils.h"
#include "third_party/skia/include/core/SkColor.h"
#include "third_party/skia/include/core/SkMatrix.h"
#include "third_party/skia/include/core/SkShader.h"
#include "third_party/skia/include/effects/SkGradientShader.h"
#include <algorithm>

typedef Vector<SkScalar, 8> ColorStopOffsetVector;
typedef Vector<SkColor, 8> ColorStopColorVector;

namespace blink {

Gradient::Gradient(const FloatPoint& p0, const FloatPoint& p1)
    : m_p0(p0),
      m_p1(p1),
      m_r0(0),
      m_r1(0),
      m_aspectRatio(1),
      m_radial(false),
      m_stopsSorted(false),
      m_drawInPMColorSpace(false),
      m_spreadMethod(SpreadMethodPad) {}

Gradient::Gradient(const FloatPoint& p0,
                   float r0,
                   const FloatPoint& p1,
                   float r1,
                   float aspectRatio)
    : m_p0(p0),
      m_p1(p1),
      m_r0(r0),
      m_r1(r1),
      m_aspectRatio(aspectRatio),
      m_radial(true),
      m_stopsSorted(false),
      m_drawInPMColorSpace(false),
      m_spreadMethod(SpreadMethodPad) {}

Gradient::~Gradient() {}

static inline bool compareStops(const Gradient::ColorStop& a,
                                const Gradient::ColorStop& b) {
  return a.stop < b.stop;
}

void Gradient::addColorStop(const Gradient::ColorStop& stop) {
  if (m_stops.isEmpty()) {
    m_stopsSorted = true;
  } else {
    m_stopsSorted = m_stopsSorted && compareStops(m_stops.back(), stop);
  }

  m_stops.push_back(stop);
  m_cachedShader.reset();
}

void Gradient::sortStopsIfNecessary() {
  if (m_stopsSorted)
    return;

  m_stopsSorted = true;

  if (!m_stops.size())
    return;

  std::stable_sort(m_stops.begin(), m_stops.end(), compareStops);
}

void Gradient::setSpreadMethod(GradientSpreadMethod spreadMethod) {
  // FIXME: Should it become necessary, allow calls to this method after
  // |m_gradient| has been set.
  DCHECK(!m_cachedShader);

  if (m_spreadMethod == spreadMethod)
    return;

  m_spreadMethod = spreadMethod;
}

void Gradient::setDrawsInPMColorSpace(bool drawInPMColorSpace) {
  if (drawInPMColorSpace == m_drawInPMColorSpace)
    return;

  m_drawInPMColorSpace = drawInPMColorSpace;
  m_cachedShader.reset();
}

// Determine the total number of stops needed, including pseudo-stops at the
// ends as necessary.
static size_t totalStopsNeeded(const Gradient::ColorStop* stopData,
                               size_t count) {
  // N.B.: The tests in this function should kept in sync with the ones in
  // fillStops(), or badness happens.
  const Gradient::ColorStop* stop = stopData;
  size_t countUsed = count;
  if (count < 1 || stop->stop > 0.0)
    countUsed++;
  stop += count - 1;
  if (count < 1 || stop->stop < 1.0)
    countUsed++;
  return countUsed;
}

// FIXME: This would be more at home as Color::operator SkColor.
static inline SkColor makeSkColor(const Color& c) {
  return SkColorSetARGB(c.alpha(), c.red(), c.green(), c.blue());
}

// Collect sorted stop position and color information into the pos and colors
// buffers, ensuring stops at both 0.0 and 1.0. The buffers must be large
// enough to hold information for all stops, including the new endpoints if
// stops at 0.0 and 1.0 aren't already included.
static void fillStops(const Gradient::ColorStop* stopData,
                      size_t count,
                      ColorStopOffsetVector& pos,
                      ColorStopColorVector& colors) {
  const Gradient::ColorStop* stop = stopData;
  size_t start = 0;
  if (count < 1) {
    // A gradient with no stops must be transparent black.
    pos[0] = WebCoreFloatToSkScalar(0.0);
    colors[0] = SK_ColorTRANSPARENT;
    start = 1;
  } else if (stop->stop > 0.0) {
    // Copy the first stop to 0.0. The first stop position may have a slight
    // rounding error, but we don't care in this float comparison, since
    // 0.0 comes through cleanly and people aren't likely to want a gradient
    // with a stop at (0 + epsilon).
    pos[0] = WebCoreFloatToSkScalar(0.0);
    colors[0] = makeSkColor(stop->color);
    start = 1;
  }

  for (size_t i = start; i < start + count; i++) {
    pos[i] = WebCoreFloatToSkScalar(stop->stop);
    colors[i] = makeSkColor(stop->color);
    ++stop;
  }

  // Copy the last stop to 1.0 if needed. See comment above about this float
  // comparison.
  if (count < 1 || (--stop)->stop < 1.0) {
    pos[start + count] = WebCoreFloatToSkScalar(1.0);
    colors[start + count] = colors[start + count - 1];
  }
}

sk_sp<SkShader> Gradient::createShader(const SkMatrix& localMatrix) {
  sortStopsIfNecessary();
  ASSERT(m_stopsSorted);

  size_t countUsed = totalStopsNeeded(m_stops.data(), m_stops.size());
  ASSERT(countUsed >= 2);
  ASSERT(countUsed >= m_stops.size());

  ColorStopOffsetVector pos(countUsed);
  ColorStopColorVector colors(countUsed);
  fillStops(m_stops.data(), m_stops.size(), pos, colors);

  SkShader::TileMode tile = SkShader::kClamp_TileMode;
  switch (m_spreadMethod) {
    case SpreadMethodReflect:
      tile = SkShader::kMirror_TileMode;
      break;
    case SpreadMethodRepeat:
      tile = SkShader::kRepeat_TileMode;
      break;
    case SpreadMethodPad:
      tile = SkShader::kClamp_TileMode;
      break;
  }

  sk_sp<SkShader> shader;
  uint32_t shouldDrawInPMColorSpace =
      m_drawInPMColorSpace ? SkGradientShader::kInterpolateColorsInPremul_Flag
                           : 0;
  if (m_radial) {
    SkMatrix adjustedLocalMatrix = localMatrix;

    if (m_aspectRatio != 1) {
      // CSS3 elliptical gradients: apply the elliptical scaling at the
      // gradient center point.
      adjustedLocalMatrix.preTranslate(m_p0.x(), m_p0.y());
      adjustedLocalMatrix.preScale(1, 1 / m_aspectRatio);
      adjustedLocalMatrix.preTranslate(-m_p0.x(), -m_p0.y());
      ASSERT(m_p0 == m_p1);
    }

    // Since the two-point radial gradient is slower than the plain radial,
    // only use it if we have to.
    if (m_p0 == m_p1 && m_r0 <= 0.0f) {
      shader = SkGradientShader::MakeRadial(
          m_p1.data(), m_r1, colors.data(), pos.data(),
          static_cast<int>(countUsed), tile, shouldDrawInPMColorSpace,
          &adjustedLocalMatrix);
    } else {
      // The radii we give to Skia must be positive. If we're given a
      // negative radius, ask for zero instead.
      SkScalar radius0 = m_r0 >= 0.0f ? WebCoreFloatToSkScalar(m_r0) : 0;
      SkScalar radius1 = m_r1 >= 0.0f ? WebCoreFloatToSkScalar(m_r1) : 0;
      shader = SkGradientShader::MakeTwoPointConical(
          m_p0.data(), radius0, m_p1.data(), radius1, colors.data(), pos.data(),
          static_cast<int>(countUsed), tile, shouldDrawInPMColorSpace,
          &adjustedLocalMatrix);
    }
  } else {
    SkPoint pts[2] = {m_p0.data(), m_p1.data()};
    shader = SkGradientShader::MakeLinear(
        pts, colors.data(), pos.data(), static_cast<int>(countUsed), tile,
        shouldDrawInPMColorSpace, &localMatrix);
  }

  if (!shader) {
    // use last color, since our "geometry" was degenerate (e.g. radius==0)
    shader = SkShader::MakeColorShader(colors[countUsed - 1]);
  }

  return shader;
}

void Gradient::applyToPaint(SkPaint& paint, const SkMatrix& localMatrix) {
  if (!m_cachedShader || localMatrix != m_cachedShader->getLocalMatrix())
    m_cachedShader = createShader(localMatrix);

  paint.setShader(m_cachedShader);

  // Legacy behavior: gradients are always dithered.
  paint.setDither(true);
}

}  // namespace blink