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chromium / angle / angle / refs/heads/main / . / extensions / ANGLE_shader_pixel_local_storage.txt
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Name
ANGLE_shader_pixel_local_storage
Name Strings
GL_ANGLE_shader_pixel_local_storage
GL_ANGLE_shader_pixel_local_storage_coherent
Contact
Chris Dalton (chris 'at' rive.app)
Contributors
Chris Dalton, Rive
Kenneth Russell, Google Inc.
Shahbaz Youssefi, Google Inc.
Kelsey Gilbert, Mozilla Corp.
Geoff Lang, Google Inc.
Kimmo Kinnunen, Apple Inc.
Contributors to the EXT_shader_pixel_local_storage specification
Contributors to the ARB_fragment_shader_interlock specification
Contributors to the INTEL_fragment_shader_ordering specification
Contributors to the EXT_shader_framebuffer_fetch specification
Contributors to the ARB_shader_image_load_store specification
Contributors to the QCOM_tiled_rendering specification
Contributors to the KHR_blend_equation_advanced specification
Contributors to the NV_texture_barrier specification
Contributors to the (Vulkan) EXT_fragment_shader_interlock specification
Contributors to the (Vulkan) ARM_rasterization_order_attachment_access specification
Status
Incomplete
Version
Last Modified Date: Aug 18, 2022
Author Revision: 1
Number
OpenGL ES Extension XX
Dependencies
OpenGL ES 3.0 and GLSL ES 3.00 are required.
This extension is written against the OpenGL ES 3.0 specification and the
OpenGL ES Shading Language 3.00 specification.
This extension interacts with ANGLE_robust_client_memory.
This extension interacts with ANGLE_request_extension.
This extension interacts with ANGLE_provoking_vertex.
This extension interacts with EXT_blend_func_extended.
This extension interacts with EXT_clip_control.
This extension interacts with EXT_clip_cull_distance.
This extension interacts with EXT_depth_clamp.
This extension interacts with EXT_draw_buffers_indexed.
This extension interacts with KHR_blend_equation_advanced.
This extension interacts with KHR_debug.
This extension interacts with NV_scissor_exclusive.
This extension interacts with OES_draw_buffers_indexed.
This extension interacts with OES_sample_variables.
This extension interacts with OpenGL ES 3.1.
This extension interacts with GLSL ES 3.10.
Overview
A major feature missing from WebGL is the ability to access rendering
results from fragment shaders and perform tasks like programmable blending.
This is especially desirable on Tile-Based Deferred Rendering (TBDR)
architectures, as it can be implemented entirely on-chip to achieve maximum
performance.
Capabilities in this area vary widely, but it is the case that all major GPU
vendors, on all major APIs, have some mechanism, direct or indirect, whereby
a fragment shader can access prior rendering results. The intent of this
extension is to condense this myriad of hardware and API features into a
simple interface with straightforward implementation(s) on every graphics
API.
Similar to EXT_shader_pixel_local_storage, this extension provides a means
for fragment shaders to load and store user-defined data associated with the
pixel being covered. The data is accessed via GLSL built-in functions
pixelLocalLoadANGLE() and pixelLocalStoreANGLE(). Only the current pixel's
data can be accessed; data associated with other pixels is not accessible to
the fragment shader. Pixel local storage persists across all fragment
invocations and across all draws issued between OpenGL ES API calls
BeginPixelLocalStorageANGLE() and EndPixelLocalStorageANGLE(), even if the
application binds different shader programs.
Applications define custom, formatted planes of pixel local storage data, up
to an implementation-dependent maximum, using the OpenGL ES API functions
FramebufferMemorylessPixelLocalStorageANGLE() and
FramebufferTexturePixelLocalStorageANGLE(). These methods behave similarly
to FramebufferTextureLayer(). Fragment shaders access a specific local
storage plane using one of the opaque GLSL types {pixelLocalANGLE,
ipixelLocalANGLE, upixelLocalANGLE}, which are analogous to samplers or
images.
This extension provides two different extension string entries:
- GL_ANGLE_shader_pixel_local_storage: Provides the new pixel local
storage functionality, but each pixel may only be touched once in any
single rendering pass. The command PixelLocalStorageBarrierANGLE() is
provided to indicate a boundary between passes. Rendering the same
pixel twice without a barrier can yield incorrect results. However,
"incorrect" does _not_ mean they can be random, uninitialized, or
leaked from outside the current draw framebuffer; any artifacts are
strictly a result of race conditions between overlapping fragment
invocations involved in the current rendering pass.
- GL_ANGLE_shader_pixel_local_storage_coherent: Guarantees that pixel
local storage operations touching the same pixel are invoked
synchronously and in API primitive order. No barriers are required and
render passes can emit overlapping fragments.
Some implementations may support GL_ANGLE_shader_pixel_local_storage without
supporting GL_ANGLE_shader_pixel_local_storage_coherent.
A note on performance: On some platforms, this feature will be polyfilled
with shader images. While every implementation can be expected to run
reasonably fast, certain platforms may see some performance degradation at
times from using pixel local storage instead of the normal raster pipeline.
As always, benchmark and consider other options before using pixel local
storage.
IP Status
No known IP claims.
New Procedures and Functions
void FramebufferMemorylessPixelLocalStorageANGLE(int plane,
enum internalformat)
void FramebufferTexturePixelLocalStorageANGLE(int plane,
uint backingtexture,
int level,
int layer)
void FramebufferPixelLocalClearValue{f,i,ui}vANGLE(int plane,
const T value[])
void BeginPixelLocalStorageANGLE(sizei n, const enum loadops[])
void EndPixelLocalStorageANGLE(sizei n, const enum storeops[])
void PixelLocalStorageBarrierANGLE()
void FramebufferPixelLocalStorageInterruptANGLE()
void FramebufferPixelLocalStorageRestoreANGLE()
void GetFramebufferPixelLocalStorageParameter{f,i}vANGLE(int plane,
enum pname,
T *params)
(the following commands are supported only if ANGLE_robust_client_memory is
supported)
void GetFramebufferPixelLocalStorageParameter{f,i}vRobustANGLE(int plane,
enum pname,
GLsizei bufSize,
GLsizei *length,
T *params)
New Tokens
Accepted by the <pname> parameter of GetIntegerv():
MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE 0x96E0
MAX_COLOR_ATTACHMENTS_WITH_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE 0x96E1
MAX_COMBINED_DRAW_BUFFERS_AND_PIXEL_LOCAL_STORAGE_PLANES_ANGLE 0x96E2
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE 0x96E3
Accepted as array elements in the <loadops> parameter of
BeginPixelLocalStorageANGLE():
LOAD_OP_ZERO_ANGLE 0x96E4
LOAD_OP_CLEAR_ANGLE 0x96E5
LOAD_OP_LOAD_ANGLE 0x96E6
Accepted as array elements in the <storeops> parameter of
EndPixelLocalStorageANGLE():
STORE_OP_STORE_ANGLE 0x96E7
Accepted by the <pname> parameter of
GetFramebufferPixelLocalStorageParameterivANGLE() and
GetFramebufferPixelLocalStorageParameterivRobustANGLE():
PIXEL_LOCAL_FORMAT_ANGLE 0x96E8
PIXEL_LOCAL_TEXTURE_NAME_ANGLE 0x96E9
PIXEL_LOCAL_TEXTURE_LEVEL_ANGLE 0x96EA
PIXEL_LOCAL_TEXTURE_LAYER_ANGLE 0x96EB
Accepted by the <pname> parameter of
GetFramebufferPixelLocalStorageParameterfvANGLE() and
GetFramebufferPixelLocalStorageParameterfvRobustANGLE():
PIXEL_LOCAL_CLEAR_VALUE_FLOAT_ANGLE 0x96EC
Accepted by the <pname> parameter of
GetFramebufferPixelLocalStorageParameterivANGLE() and
GetFramebufferPixelLocalStorageParameterivRobustANGLE():
PIXEL_LOCAL_CLEAR_VALUE_INT_ANGLE 0x96ED
PIXEL_LOCAL_CLEAR_VALUE_UNSIGNED_INT_ANGLE 0x96EE
New GLSL Opaque Types
pixelLocalANGLE
ipixelLocalANGLE
upixelLocalANGLE
New GLSL Built-in Functions
gvec4 pixelLocalLoadANGLE(gpixelLocalANGLE)
void pixelLocalStoreANGLE(gpixelLocalANGLE, gvec4 value)
Additions to the OpenGL ES Specification, Version 3.0.6
Modify Chapter 2 "OpenGL ES Operation"
(Insert a new numbered section before 2.14 "Asynchronous Queries".)
Section 2.X "Pixel Local Storage"
Pixel local storage provides a means for fragment shaders to load and store
user-defined data associated with the pixel being covered. Pixel local
storage is configured on a framebuffer as described in Section 4.4.2.X
"Configuring Pixel Local Storage on a Framebuffer". Fragment shaders may
access pixel local storage data as described in OpenGL ES Shading Language
Specification.
Pixel local storage is activated and deactivated for the current draw
framebuffer using the commands:
void BeginPixelLocalStorageANGLE(sizei n, const enum loadops[])
void EndPixelLocalStorageANGLE(sizei n, const enum storeops[])
Parameters:
* <n> specifies the length of the <loadops> or <storeops> array.
* <loadops> specifies an array of <n> pixel local storage "Load
Operations", whose ith element describes the Load Operation to
perform on the ith pixel local storage plane. Supported Load
Operations are listed in Table X.1. Load Operations are
performed on the entire area of each plane, irrespective of
scissor or viewport state.
Load Operation Description
-----------------------------------------------------------------------
LOAD_OP_ZERO_ANGLE Clear all components of the pixel local storage
plane to 0. This is recommended over
LOAD_OP_CLEAR_ANGLE, as it is more likely to be
performant on all implementations.
LOAD_OP_CLEAR_ANGLE Clear the pixel local storage plane to its
framebuffer's ith clear value of corresponding
type. Pixel local clear values are specified
with
FramebufferPixelLocalClearValue{f,i,ui}vANGLE(),
as described in section 4.4.2.Y "Pixel Local
Clear State". If the magnitude of any component
of the clear value is too large to be
represented in the plane's internalformat, it
is clamped.
LOAD_OP_LOAD_ANGLE Load the contents of the bound texture image
into pixel local storage. This Load Operation
is only valid for pixel local storage planes
that have a texture binding. Texture bindings
are established with
FramebufferTexturePixelLocalStorageANGLE() as
described in section 4.4.2.X "Configuring Pixel
Local Storage on a Framebuffer".
DONT_CARE Leave the initial contents of the pixel local
storage plane undefined, favoring speed, and
with the caveat that they are _not_ leaked from
outside the current draw framebuffer.
Table X.1: Pixel local storage Load Operations.
* <storeops> specifies an array of <n> pixel local storage "Store
Operations", whose ith element describes the Store Operation
to perform on the backing texture of the ith pixel local
storage plane. The store operation is ignored if its plane is
memoryless. Supported Store Operations are listed in Table
X.2.
Store Operation Description
-----------------------------------------------------------------------
STORE_OP_STORE_ANGLE Update the the bound texture image to reflect
the pixel local storage contents.
DONT_CARE Leave the bound texture image contents
undefined, with the caveat that they are either
unchanged, or not leaked from outside the
current draw framebuffer.
Table X.2: Pixel local storage Store Operations.
Errors generated by BeginPixelLocalStorageANGLE():
* INVALID_FRAMEBUFFER_OPERATION is generated if the default framebuffer
object name 0 is bound to DRAW_FRAMEBUFFER.
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_OPERATION is generated if
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is nonzero.
* INVALID_OPERATION is generated if the value of SAMPLE_BUFFERS is 1
(i.e., if rendering to a multisampled framebuffer).
* INVALID_OPERATION is generated if DITHER is enabled.
* INVALID_OPERATION is generated if RASTERIZER_DISCARD is enabled.
* INVALID_OPERATION is generated if TRANSFORM_FEEDBACK_ACTIVE is TRUE.
* INVALID_OPERATION is generated if BLEND_DST_ALPHA, BLEND_DST_RGB,
BLEND_SRC_ALPHA, or BLEND_SRC_RGB, for any draw buffer, is a blend
function requiring the secondary color input, as specified in
EXT_blend_func_extended (SRC1_COLOR_EXT, ONE_MINUS_SRC1_COLOR_EXT,
SRC1_ALPHA_EXT, ONE_MINUS_SRC1_ALPHA_EXT).
* INVALID_OPERATION is generated if BLEND_EQUATION_RGB and/or
BLEND_EQUATION_ALPHA is an advanced blend equation defined in
KHR_blend_equation_advanced.
* INVALID_VALUE is generated if
<n> < 1 or <n> > MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE.
* INVALID_FRAMEBUFFER_OPERATION is generated if the draw framebuffer has
an image attached to any color attachment point on or after:
COLOR_ATTACHMENT0 +
MAX_COLOR_ATTACHMENTS_WITH_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE
* INVALID_FRAMEBUFFER_OPERATION is generated if the draw framebuffer has
an image attached to any color attachment point on or after:
COLOR_ATTACHMENT0 +
MAX_COMBINED_DRAW_BUFFERS_AND_PIXEL_LOCAL_STORAGE_PLANES_ANGLE - <n>
* INVALID_VALUE is generated if <loadops> is NULL.
* INVALID_ENUM is generated if <loadops>[0..<n>-1] is not one of the Load
Operations enumerated in Table X.1.
* INVALID_OPERATION is generated if a pixel local storage plane at index
[0..<n>-1] is in a deinitialized state.
* INVALID_OPERATION is generated if <loadops>[0..<n>-1] is
LOAD_OP_LOAD_ANGLE and the pixel local storage plane at that same index
is memoryless.
* INVALID_OPERATION is generated if all enabled, texture-backed pixel
local storage planes do not have the same width and height.
* INVALID_OPERATION is generated if the draw framebuffer has other
attachments, and its enabled, texture-backed pixel local storage planes
do not have identical dimensions with the rendering area.
(The rendering area is defined in section 4.4.1 "Binding and Managing
Framebuffer Objects" as the intersection of rectangles having a lower
left of [0, 0] and an upper right of [width, height] for each
attachment.)
* INVALID_OPERATION is generated if the draw framebuffer has no
attachments and no enabled, texture-backed pixel local storage planes.
* INVALID_OPERATION is generated if a single texture image is bound to
more than one active pixel local storage plane.
* INVALID_OPERATION is generated if a single texture image is
simultaneously bound to a pixel local storage plane and attached to the
draw framebuffer.
Errors generated by EndPixelLocalStorageANGLE():
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_OPERATION is generated if
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is zero.
* INVALID_VALUE is generated if
<n> != PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE.
* INVALID_ENUM is generated if
<storeops>[0..PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE-1] is not one of
the Store Operations enumerated in Table X.2.
After a successful call to BeginPixelLocalStorageANGLE(), the pixel local
storage planes indexed in the range [0..<n>-1] are fully activated,
initialized and available for fragment shaders to read and write.
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is also updated to equal <n>.
Pixel local storage data will persist across all fragment invocations and
across all draws issued until the application calls
EndPixelLocalStorageANGLE(), even if the application binds different shader
programs. In order to make this guarantee, the the OpenGL ES API only allows
a limited set of commands while PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is
nonzero. All other commands generate INVALID_OPERATION. Valid commands while
pixel local storage is active are listed in Table X.3.
ActiveTexture
BindBuffer
BindBufferBase
BindBufferRange
BindSampler
BindTexture
BindVertexArray
BlendEquationSeparatei*
BlendEquationi*
BlendFuncSeparatei*
BlendFunci*
BufferData
BufferSubData
CheckFramebufferStatus
ClearBuffer*
ClipControlEXT
ColorMaski*
CullFace
DebugMessageCallback*
DebugMessageControl*
DebugMessageInsert*
Delete*
DepthFunc
DepthMask
DepthRangef
Disable
DisableVertexAttribArray
Disablei*
DispatchComputeIndirect
DrawArrays*
DrawElements*
DrawRangeElements*
Enable
EnableClientState
EnableVertexAttribArray
Enablei*
EndPixelLocalStorageANGLE
FlushMappedBufferRange
FramebufferPixelLocalStorageInterruptANGLE
FrontFace
Gen*
Get*
Is*
MapBufferRange
ObjectLabel*
ObjectPtrLabel*
PixelLocalStorageBarrierANGLE
PolygonOffset*
PopDebugGroup*
ProvokingVertexANGLE
PushDebugGroup*
SamplerParameter*
Scissor
StencilFunc
StencilFuncSeparate
StencilMask
StencilMaskSeparate
StencilOp
StencilOpSeparate
TexParameter*
Uniform*
UnmapBuffer
UseProgram
ValidateProgram
VertexAttrib*
Viewport
Table X.3: Valid commands while PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE
is nonzero.
Additional restrictions also go into effect when
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is nonzero:
* INVALID_OPERATION is generated by Enable(), Disable() if <cap> is not
one of: CULL_FACE, DEBUG_OUTPUT, DEBUG_OUTPUT_SYNCHRONOUS,
DEPTH_CLAMP_EXT, DEPTH_TEST, POLYGON_OFFSET_FILL,
PRIMITIVE_RESTART_FIXED_INDEX, SCISSOR_TEST, SCISSOR_TEST_EXCLUSIVE_NV,
STENCIL_TEST, CLIP_DISTANCE[0..7]_EXT
* INVALID_OPERATION is generated by ClearBufferfv(), ClearBufferiv(),
ClearBufferuiv() if <buffer> is COLOR and any of the following are true:
<buffer> >= MAX_COLOR_ATTACHMENTS_WITH_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE
<buffer> >=
(MAX_COMBINED_DRAW_BUFFERS_AND_PIXEL_LOCAL_STORAGE_PLANES_ANGLE -
ACTIVE_PIXEL_LOCAL_STORAGE_PLANES_ANGLE)
* INVALID_OPERATION is generated by Enablei*(), Disablei*() if <cap> is
not one of: BLEND, SCISSOR_TEST, SCISSOR_TEST_EXCLUSIVE_NV
* INVALID_OPERATION is generated by Enablei*(), Disablei*() if <cap> is
BLEND and any of the following are true:
<index> >= MAX_COLOR_ATTACHMENTS_WITH_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE
<index> >=
(MAX_COMBINED_DRAW_BUFFERS_AND_PIXEL_LOCAL_STORAGE_PLANES_ANGLE -
ACTIVE_PIXEL_LOCAL_STORAGE_PLANES_ANGLE)
* INVALID_OPERATION is generated by BlendEquationi*(),
BlendEquationSeparatei*(), BlendFunci*(), BlendFuncSeparatei*(),
ColorMaski*() if any of the following are true:
<buf> >= MAX_COLOR_ATTACHMENTS_WITH_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE
<buf> >=
(MAX_COMBINED_DRAW_BUFFERS_AND_PIXEL_LOCAL_STORAGE_PLANES_ANGLE -
ACTIVE_PIXEL_LOCAL_STORAGE_PLANES_ANGLE)
* INVALID_OPERATION is generated by BlendFunci*() and
BlendFuncSeparatei*() if <srcRGB>, <dstRGB>, <srcAlpha>, or <dstAlpha>
is a blend function requiring the secondary color input, as specified in
EXT_blend_func_extended (SRC1_COLOR_EXT, ONE_MINUS_SRC1_COLOR_EXT,
SRC1_ALPHA_EXT, ONE_MINUS_SRC1_ALPHA_EXT).
* INVALID_OPERATION is generated by BlendEquationi*() if <mode> is one of
the advanced blend equations defined in KHR_blend_equation_advanced.
* INVALID_OPERATION is generated if a draw is issued with a fragment
shader that accesses a texture bound to pixel local storage.
* INVALID_OPERATION is generated if a draw is issued with a fragment
shader that has a pixel local uniform bound to an inactive pixel local
storage plane.
* INVALID_OPERATION is generated if a draw is issued with a fragment
shader that does _not_ have a pixel local uniform bound to an _active_
pixel local storage plane (i.e., the fragment shader must declare
uniforms bound to every single active pixel local storage plane).
This is because many backend implementations need to account for every
active pixel local storage plane, even if the application code does not
access it during a particular shader invocation.
* INVALID_OPERATION is generated if a draw is issued with a fragment
shader that has a pixel local storage uniform whose format layout
qualifier does not identically match the internalformat of its
associated pixel local storage plane on the current draw framebuffer, as
enumerated in Table X.4.
Because of the "implementation-dependent" clause of the framebuffer
completeness test, and because a pixel local storage implementation may add
additional attachments to the underlying framebuffer object, it is strongly
advised that an application also check to see if the framebuffer is complete
after BeginPixelLocalStorageANGLE() and prior to rendering. (See section
4.4.4.2 "Whole Framebuffer Completeness".)
If BeginPixelLocalStorageANGLE() generates an error,
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is not modified, and a balancing
call to EndPixelLocalStorageANGLE() may therefore also generate an error.
When PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is zero, any draw issued with a
fragment shader that declares pixel local storage uniforms generates an
INVALID_FRAMEBUFFER_OPERATION error.
Section 2.X.1 "Non-coherent Pixel Local Storage"
When GL_ANGLE_shader_pixel_local_storage_coherent is _not_ supported, and
pixel local storage is active, applications must also split their rendering
of pixel local storage into separate passes, none of which touch an
individual pixel more than once. The command:
void PixelLocalStorageBarrierANGLE()
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_OPERATION is generated if
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is zero.
delimits a boundary between distinct, non-self-overlapping rendering passes.
Pixel local storage loads issued after the barrier will reflect stores
issued prior to the barrier, and stores issued after the barrier will not
execute until all accesses initiated prior to the barrier are complete.
Rendering to the same pixel more than once without a barrier in between can
yield incorrect results in pixel local storage, however, "incorrect" does
_not_ mean they can be random, uninitialized, or leaked from outside the
current draw framebuffer. Any artifacts are strictly a result of race
conditions between overlapping fragment invocations involved in the current
rendering pass.
Section 2.X.2 "Interrupting Pixel Local Storage"
An application may need to interrupt a pixel local storage rendering pass.
One example of this may be a browser implementing WebGL. The command:
void FramebufferPixelLocalStorageInterruptANGLE()
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if the current interrupt
count on the draw framebuffer is equal to 255.
Increments an interrupt counter on the current draw framebuffer. When the
counter increments from 0 to 1, and PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE
is nonzero, this command also ends pixel local storage using
STORE_OP_STORE_ANGLE for every plane. The contents of any memoryless planes
are lost. The counter value cannot be incremented greater than 255. This
command is ignored when the default framebuffer object name 0 is bound. When
a framebuffer's pixel local storage interupt counter is nonzero, it is
considered to be in an "interrupted" state.
The command:
void FramebufferPixelLocalStorageRestoreANGLE()
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is not in an interrupted state.
Decrements the pixel local storage interrupt counter on the current draw
framebuffer. When the counter decrements from 1 to 0, and
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE was nonzero at the time this
framebuffer entered an interrupted state, the command also begins pixel
local storage using LOAD_OP_LOAD_ANGLE for texture backed planes and
DONT_CARE for memoryless planes. The number of planes activated is equal to
the value of PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE at the time this
framebuffer entered an interrupted state. This command is ignored when the
default framebuffer object name 0 is bound.
Modify Section 4.4.2 "Attaching Images to Framebuffer Objects"
(Add a new paragraph to 4.4.2.3 "Attaching Renderbuffer Images to a
Framebuffer".)
If a renderbuffer object is deleted while its image is attached to the
currently bound draw framebuffer, and pixel local storage is active, then it
is as if EndPixelLocalStorageANGLE() had been called with
<n>=PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE and <storeops> of
STORE_OP_STORE_ANGLE.
(Add a new paragraph to 4.4.2.4 "Attaching Texture Images to a Framebuffer".)
If a texture object is deleted while its image is attached to the currently
bound draw framebuffer, and pixel local storage is active, then it is as if
EndPixelLocalStorageANGLE() had been called with
<n>=PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE and <storeops> of
STORE_OP_STORE_ANGLE.
(Insert two new numbered section after 4.4.2.4 "Attaching Texture Images to a
Framebuffer".)
Section 4.4.2.X "Configuring Pixel Local Storage on a Framebuffer"
The GL provides an array of configurable pixel local storage planes on
framebuffer objects. These planes are numbered beginning with zero, with the
total number of pixel local storage planes provided given by the
implementation-dependent constant MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE.
Fragment shaders may access pixel local storage data as described in OpenGL
ES Shading Language Specification. Initially, pixel local storage planes are
in a deinitialized state and are unusable.
A memoryless pixel local storage plane may be established on the current
draw framebuffer by calling:
void FramebufferMemorylessPixelLocalStorageANGLE(int plane,
enum internalformat)
Parameters:
* <plane> identifies the pixel local storage plane index.
* <internalformat> selects the data format, as enumerated in Table X.4.
internalformat Clear Value Type Pixel Local Type format qualifier
-----------------------------------------------------------------------
RGBA8 FLOAT pixelLocalANGLE rgba8
RGBA8I INT ipixelLocalANGLE rgba8i
RGBA8UI UNSIGNED_INT upixelLocalANGLE rgba8ui
R32F FLOAT pixelLocalANGLE r32f
R32UI UNSIGNED_INT upixelLocalANGLE r32ui
Table X.4: Supported pixel local storage internalformats, with the Clear
Value Type used by BeginPixelLocalStorageANGLE(), and their required
corresponding GLSL Pixel Local Type and format layout qualifier.
Note that all pixel local storage formats consume exactly 4 bytes of
storage.
Note that r32i is excluded from this table because it is not supported
by EXT_shader_pixel_local_storage.
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if the default framebuffer
object name 0 is bound to DRAW_FRAMEBUFFER.
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_OPERATION is generated if
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is nonzero.
* INVALID_VALUE is generated if
<plane> < 0 or <plane> >= MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE.
* INVALID_ENUM is generated if <internalformat> is not one of the
acceptable values in Table X.4, or NONE.
If <internalformat> is NONE, the pixel local storage plane at index <plane>
is deinitialized and any internal storage is released.
Otherwise, this call establishes a formatted plane of pixel local storage
data at index <plane>, accessible exclusively to fragment shaders, whose
liftetime will be scoped between calls to BeginPixelLocalStorageANGLE() and
EndPixelLocalStorageANGLE(). The pixel local storage plane is "memoryless"
from the application's perspective; its contents are cleared upon calling
BeginPixelLocalStorageANGLE(), and its contents are lost after the
application calls EndPixelLocalStorageANGLE(). The implementation will make
a best effort to store this data exclusively in high performance local
caches, e.g., tiled memory, but accessing the data may still result in
memory transactions on some platforms.
Additionally, the GL supports binding a layer of an immutable texture object
to pixel local storage. In this scenario, the pixel local storage data is
not lost upon calling EndPixelLocalStorageANGLE(), but rather, will be
stored in the given texture image. Such behavior is useful for applications
such as blending in the fragment shader, where the application renders to
pixel local storage instead of a color attachment.
When a texture image is bound to pixel local storage, the application may
also choose to initialize the pixel local storage plane using its bound
texture image contents during BeginPixelLocalStorageANGLE(), by passing Load
Operation LOAD_OP_LOAD_ANGLE.
An immutable texture layer image may be bound to a pixel local storage plane
on the current draw framebuffer by calling:
void FramebufferTexturePixelLocalStorageANGLE(int plane,
uint backingtexture,
int level,
int layer)
Parameters:
* <plane> identifies the pixel local storage plane index.
* <backingtexture> specifies the name of an existing immutable texture
object to bind.
* <level> selectes the mipmap level to bind.
* <layer> specifies the texture layer to bind:
- Zero if <backingtexture> is a TEXTURE_2D
- The array index to bind if <backingtexture> is a TEXTURE_2D_ARRAY
- The Z coordinate to bind if <backingtexture> is a TEXTURE_3D
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if the default framebuffer
object name 0 is bound to DRAW_FRAMEBUFFER.
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_OPERATION is generated if
PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is nonzero.
* INVALID_VALUE is generated if
<plane> < 0 or <plane> >= MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE.
* INVALID_OPERATION is generated if <backingtexture> is not the name of an
existing immutable texture object, or zero.
* INVALID_OPERATION is generated if <backingtexture> is nonzero and not of
type TEXTURE_2D, TEXTURE_2D_ARRAY, or TEXTURE_3D.
* INVALID_VALUE is generated if <backingtexture> is nonzero and
<level> < 0.
* INVALID_VALUE is generated if <backingtexture> is nonzero and
<level> >= the immutable number of mipmap levels in <backingtexture>.
* INVALID_VALUE is generated if <backingtexture> is nonzero and
<layer> < 0.
* INVALID_VALUE is generated if <backingtexture> is nonzero and
<layer> >= the immutable number of texture layers in <backingtexture>.
* INVALID_ENUM is generated if <backingtexture> is nonzero and its
internalformat is not one of the acceptable values in Table X.4.
If <backingtexture> is 0, <level> and <layer> are ignored and the pixel
local storage plane <plane> is deinitialized.
Otherwise, this call establishes a formatted plane of pixel local storage
data at index <plane>, whose contents are bound to the given texture layer
image.
When a texture object is deleted, any pixel local storage plane to which it
is bound is automatically deinitialized.
If a texture object is deleted while its image is bound to a pixel local
storage plane on the currently bound draw framebuffer, and pixel local
storage is active, then it is as if EndPixelLocalStorageANGLE() had been
called with <n>=PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE and <storeops> of
STORE_OP_STORE_ANGLE.
Section 4.4.2.Y "Pixel Local Clear State"
Each pixel local storage plane on a framebuffer has state for three separate
clear values: a 4-component vector of type FLOAT, INT, and UNSIGNED_INT.
When the Load Operation LOAD_OP_CLEAR_ANGLE is executed, a pixel local
storage plane is cleared to the value whose type corresponds to its
internalformat. (See Table X.4.) Clear values are set with the commands:
void FramebufferPixelLocalClearValuefvANGLE(int plane,
const float value[])
void FramebufferPixelLocalClearValueivANGLE(int plane,
const int value[])
void FramebufferPixelLocalClearValueuivANGLE(int plane,
const uint value[])
Parameters:
* <plane> identifies the pixel local storage plane index.
* <value> specifies the new 4-component clear value.
Description:
Sets the clear value state of specific type for a plane of pixel local
storage on the current draw framebuffer.
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if the default framebuffer
object name 0 is bound to DRAW_FRAMEBUFFER.
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_VALUE is generated if
<plane> < 0 or <plane> >= MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE.
Modify Section 6.1 "Querying GL State"
(Insert a new numbered section after 6.1.14 "Renderbuffer Object Queries".)
Section 6.1.X "Pixel Local Storage Queries"
The application may query the state of a pixel local storage plane on the
current draw famebuffer using the commands:
void GetFramebufferPixelLocalStorageParameterfvANGLE(int plane,
enum pname,
GLsizei bufSize,
GLsizei *length,
GLfloat *params)
void GetFramebufferPixelLocalStorageParameterivANGLE(int plane,
enum pname,
GLsizei bufSize,
GLsizei *length,
GLint *params)
Parameters:
* <plane> identifies the pixel local storage plane index.
* <pname> specifies the parameter of the plane to query.
* <params> receives the value(s) for parameter <pname> of the pixel local
storage plane at index <plane>. When an error is generated, nothing is
written to <params>.
Description:
* If <pname> is PIXEL_LOCAL_FORMAT_ANGLE, <params> will contain the
internalformat of the plane from Table X.4, or NONE if the selected
pixel local storage plane is in a deinitialized state.
* If <pname> is PIXEL_LOCAL_TEXTURE_NAME_ANGLE, <params> will contain the
name of the immutable texture object which contains the image bound to
the plane, or 0 if the plane is memoryless or deinitialized.
Note that when the texture object bound to a plane is deleted, the plane
is automatically converted to memoryless. See section 4.4.2.X
"Configuring Pixel Local Storage on a Framebuffer".
* If <pname> is PIXEL_LOCAL_TEXTURE_LEVEL_ANGLE, <params> will contain the
mipmap level of the bound texture object, or 0 if the plane is
memoryless or deinitialized.
* If <pname> is PIXEL_LOCAL_TEXTURE_LAYER_ANGLE, <params> will contain the
layer of the bound texture object, or 0 if the plane is memoryless or
deinitialized.
* If <pname> is PIXEL_LOCAL_CLEAR_VALUE_FLOAT_ANGLE,
PIXEL_LOCAL_CLEAR_VALUE_INT_ANGLE, or
PIXEL_LOCAL_CLEAR_VALUE_UNSIGNED_INT_ANGLE, <params> will contain 4
values: the 4 color components of the clear value of corresponding type.
Errors:
* INVALID_FRAMEBUFFER_OPERATION is generated if the default framebuffer
object name 0 is bound to DRAW_FRAMEBUFFER.
* INVALID_FRAMEBUFFER_OPERATION is generated if pixel local storage on the
draw framebuffer is in an interrupted state. (See section 2.X.2
"Interrupting Pixel Local Storage")
* INVALID_VALUE is generated if
<plane> < 0 or <plane> >= MAX_PIXEL_LOCAL_STORAGE_PLANES_ANGLE.
* INVALID_ENUM is generated if <pname> is not in Table 6.Y, or if the
command issued is not the associated "Get Command" for <pname> in Table
6.Y.
* INVALID_VALUE is generated if <params> is NULL.
If ANGLE_robust_client_memory is supported, the alternative query commands
may also be used:
void GetFramebufferPixelLocalStorageParameterfvRobustANGLE(int plane,
enum pname,
GLsizei bufSize,
GLsizei *length,
GLfloat *params)
void GetFramebufferPixelLocalStorageParameterivRobustANGLE(int plane,
enum pname,
GLsizei bufSize,
GLsizei *length,
GLint *params)
Additional Parameters:
* <bufSize> indicates the maximum number of values that can be written to
<params>.
* <length> may be NULL. If not NULL, it receives the number of values
written to <params>. When an error is generated, nothing is written to
<length>.
Additional Errors:
* INVALID_OPERATION is generated if <bufSize> is not large enough to
receive the requested parameter.
Modify Section 6.1 "State Tables"
(Insert two new numbered tables.)
Minimum
Get Value Type Get Command Value Sec.
------------------------------------------------------------------------
MAX_PIXEL_LOCAL_STORAGE-
_PLANES_ANGLE Z+ GetIntegerv 4 4.4.2.X
MAX_COLOR_ATTACHMENTS_WITH-
_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE Z+ GetIntegerv *0! 2.X
MAX_COMBINED_DRAW_BUFFERS_AND-
_PIXEL_LOCAL_STORAGE_PLANES_ANGLE Z+ GetIntegerv 4 2.X
Table 6.X: Impementation Dependent Pixel Local Storage Limits
Note that MAX_COLOR_ATTACHMENTS_WITH_ACTIVE_PIXEL_LOCAL_STORAGE_ANGLE may be
zero, in which case the application cannot render to any other color
attachments while PIXEL_LOCAL_STORAGE_ACTIVE_PLANES_ANGLE is nonzero.
Initial
Get Value Type Get Command Value Sec.
--------------------------------------------------------------------------
PIXEL_LOCAL_STORAGE-
_ACTIVE_PLANES_ANGLE Z+ GetIntegerv 0 2.X
PIXEL_LOCAL_FORMAT- GetFramebufferPixelLocal-
_ANGLE Z+ StorageParameterivANGLE NONE 6.1.X
PIXEL_LOCAL_TEXTURE- GetFramebufferPixelLocal-
_NAME_ANGLE Z+ StorageParameterivANGLE 0 6.1.X
PIXEL_LOCAL_TEXTURE- GetFramebufferPixelLocal-
_LEVEL_ANGLE Z+ StorageParameterivANGLE 0 6.1.X
PIXEL_LOCAL_TEXTURE- GetFramebufferPixelLocal-
_LAYER_ANGLE Z StorageParameterivANGLE 0 6.1.X
PIXEL_LOCAL_CLEAR- GetFramebufferPixelLocal-
_VALUE_FLOAT_ANGLE 4*R StorageParameterfvANGLE 0,0,0,0 6.1.X
PIXEL_LOCAL_CLEAR- GetFramebufferPixelLocal-
_VALUE_INT_ANGLE 4*Z StorageParameterivANGLE 0,0,0,0 6.1.X
PIXEL_LOCAL_CLEAR_VALUE- GetFramebufferPixelLocal-
_UNSIGNED_INT_ANGLE 4*Z+ StorageParameterivANGLE 0,0,0,0 6.1.X
Table 6.Y: Pixel Local Storage State
Interactions with the ANGLE_request_extension specification
When either ANGLE_shader_pixel_local_storage or
ANGLE_shader_pixel_local_storage_coherent is enabled, the following
extensions are all implicitly enabled, if supported:
* OES_draw_buffers_indexed
* EXT_draw_buffers_indexed
* EXT_color_buffer_float
* EXT_color_buffer_half_float
* ANGLE_shader_pixel_local_storage_coherent
* ANGLE_shader_pixel_local_storage
Interactions with ANGLE_provoking_vertex, EXT_blend_func_extended,
EXT_clip_control, EXT_clip_cull_distance, EXT_depth_clamp,
EXT_draw_buffers_indexed, KHR_blend_equation_advanced, KHR_debug,
NV_scissor_exclusive, OES_draw_buffers_indexed
If any of these extensions is not supported, ignore the applicable
references to the extension itself, and to BlendEquationSeparatei*,
BlendEquationi*, BlendFuncSeparatei*, BlendFunci*, ColorMaski*,
DebugMessageCallback*, DebugMessageControl*, DebugMessageInsert*, Disablei*,
ClipControlEXT, Enablei* ObjectLabel*, ProvokingVertexANGLE,
ObjectPtrLabel*, PopDebugGroup*, PushDebugGroup*, DEBUG_OUTPUT,
DEBUG_OUTPUT_SYNCHRONOUS, SCISSOR_TEST_EXCLUSIVE_NV, CLIP_DISTANCE[0..7]_EXT
Interactions with OpenGL ES 3.1
Modify Section 8.22 "Texture Image Loads and Stores"
(Modify the final paragraph.)
Add active pixel local storage planes to the list of resource types that count
against MAX_COMBINED_SHADER_OUTPUT_RESOURCES.
Additions to the OpenGL ES Shading Language Specification, Version 3.00
Including the following line in a fragment shader controls the language
features described in this extension:
#extension GL_ANGLE_shader_pixel_local_storage : <behavior>
Where <behavior> is as specified in section 3.5.
Whether or not the application relies on the "_coherent" extension string
from the OpenGL ES API side, the language features described in this section
are identical, and fragment shaders should only enable
GL_ANGLE_shader_pixel_local_storage.
Modify Section 4.1 "Basic Types"
(Add the following new types.)
Pixel Local Types (opaque)
* pixelLocalANGLE
a handle for accessing floating-point pixel local storage data
* ipixelLocalANGLE
a handle for accessing integer pixel local storage data
* upixelLocalANGLE
a handle for accessing unsigned integer pixel local storage data
Modify Section 4.1.7 "Opaque Types"
(Insert a new numbered section after 4.1.7.1 "Samplers".)
Section 4.1.7.X "Pixel Local Storage"
Pixel local types (e.g. pixelLocalANGLE) are opaque types. They are handles
for accessing user-defined data that is associated with the pixel being
covered. They are used with the built-in functions described in section 8.X
"Pixel Local Storage Functions".
In addition to the limitations already imposed on opaque types, pixel local
types are subject to additional constraints:
* They cannot be aggregated in arrays.
* As uniforms, they must be declared at global scope; they cannot be
declared in structs or interface blocks.
* As uniforms, they are not visible to the OpenGL ES API and cannot be
accessed via GetUniformLocation() or GetActiveUniform(). (This
facilitates backends that are implemented entirely in-shader, e.g.,
EXT_shader_pixel_local_storage.)
* As uniforms, they must declare "binding" and "format" layout qualifiers,
as described in section 4.3.8.X "Pixel Local Storage Layout Qualifiers".
* As function arguments, they cannot have layout qualifiers. Any function
that accepts pixel local type(s) as arguments is inlined by the compiler,
and the bindings and formats are determined at the call site.
* They cannot be aliased; it is a compile-time error to declare two pixel
local uniforms with duplicate binding layout qualifiers.
* They can only be declared in a fragment shader.
Fragment shaders that declare pixel local storage uniforms are subject to
additional shader-wide restrictions as well:
* discard is illegal
When polyfilled with shader images, pixel local storage requires
early_fragment_tests, which causes discard to interact differently
with the depth and stencil tests.
In order to ensure identical behavior across all backends (some of
which may not have access to early_fragment_tests), we disallow
discard if pixel local storage uniforms have been declared.
* return from main() is illegal
ARB_fragment_shader_interlock functions cannot be called within flow
control, which includes any code that might execute after a return
statement. To keep things simple, and since these "interlock" calls
are automatically generated by the compiler inside of main(), we
disallow return from main() if pixel local storage uniforms have been
declared.
* assignment to gl_FragDepth(EXT) or gl_SampleMask is illegal
When polyfilled with shader images, pixel local storage requires
early_fragment_tests, which causes assignments to gl_FragDepth(EXT)
and gl_SampleMask to be ignored.
In order to ensure identical behavior across all backends, we disallow
assignment to these values if pixel local storage uniforms have been
declared.
* EXT_blend_func_extended: nonzero values of the <index> layout qualifier
are illegal
Nonzero <index> values may restrict the number of draw buffers, which
can invalidate a PLS implementation.
* EXT_blend_func_extended: multiple unassigned fragment output locations
are illegal
Since PLS may use additional internal fragment outputs, we ban all
implicit fragment output assignments while PLS is in use.
* KHR_blend_equation_advanced: "blend_support" layout qualifiers are
illegal
KHR_blend_equation_advanced is incompatible with multiple draw
buffers, which is a required feature for many PLS implementations.
Modify Section 4.3.8 "Layout Qualifiers"
(Insert a new numbered section after 4.3.8.3 "Uniform Block Layout
Qualifiers")
Section 4.3.8.X "Pixel Local Storage Layout Qualifiers"
The layout qualifier identifiers for pixel local storage types are:
layout-qualifier-id
binding = <integer-constant>
<format>
Accepable identifiers for <format> are enumerated in Table X.4.
It is a compile-time error to declare a pixel local storage uniform that
does not specify both of these layout qualifiers, or to specify a format
layout qualifier on any type other than that format's corresponding "Pixel
Local Type", as enumerated in Table X.4.
Modify Section 8 "Built-in Functions"
(Insert a new numbered section after 8.9 "Fragment Processing Functions".)
Section 8.X "Pixel Local Storage Functions"
The built-in functions defined in this section accept pixel local storage
handles (abbreviated as "PLS handles") in order to load and store data
associated with the pixel being covered.
A reference to a specific PLS plane is established by indexing into the
current draw framebuffer's PLS planes using the PLS handle's "binding"
layout qualifier. If any PLS handle references an inactive PLS plane, or a
PLS plane whose internalformat does not match the handle's format, the
shader does not execute and a draw-time error is generated in the OpenGL ES
API instead.
Syntax:
vec4 pixelLocalLoadANGLE(pixelLocalANGLE handle)
ivec4 pixelLocalLoadANGLE(ipixelLocalANGLE handle)
uvec4 pixelLocalLoadANGLE(upixelLocalANGLE handle)
Description:
Reads the current pixel's data from the PLS plane referenced by <handle>.
Syntax:
void pixelLocalStoreANGLE(pixelLocalANGLE handle, vec4 value)
void pixelLocalStoreANGLE(ipixelLocalANGLE handle, ivec4 value)
void pixelLocalStoreANGLE(upixelLocalANGLE handle, uvec4 value)
Description:
Replaces the current pixel's data with <value> in the PLS plane referenced
by <handle>. If the magnitude of <value> is too large to be represented in
the PLS format, it is clamped.
Modify Section 9 "Shading Language Grammar"
(Add the following tokens to the lexical analysis.)
PIXELLOCALANGLE IPIXELLOCALANGLE UPIXELLOCALANGLE
Interactions with GLSL ES 3.10
If GLSL ES 3.10 is supported, pixel local storage and images cannot be used
in the same shader; it is a compile time error for a shader to declare both
image uniforms and pixel local storage uniforms.
Issues
(1) EXT_shader_pixel_local_storage has a clause that PLS contents become
undefined if an application causes color data to be flushed to the
framebuffer. Can we use this extension and still guarantee the security of
WebGL?
RESOLVED: We have confirmation that all mobile vendors guarantee there's
no data leaked from outside the render pass. There can be data leaked from
normal framebuffer attachments to PLS planes, but said attachments
themselves are not shared between WebGL contexts, so should not be a
security concern.
Imagination gave the caveat that we must also initialize PLS data up front
in order to not get left-over data from a previous render pass, but this
is exactly what our API is designed to do via load operations. If
EXT_shader_pixel_local_storage2 is supported, we can clear PLS using
ClearPixelLocalStorageuiEXT(). Otherwise, we can clear or load PLS data
from a texture by issuing a fullscreen draw.
Additionally, if the browser uses virtual contexts and wishes to interrupt
a PLS render pass, it must be sure to internally call
FramebufferPixelLocalStorageInterruptANGLE() before handing off control to
the other virtual context, and FramebufferPixelLocalStorageRestoreANGLE()
again before returning control.
(2) Depending on the implementation, <loadops> of LOAD_OP_ZERO_ANGLE and
LOAD_OP_LOAD_ANGLE can have very different performance characteristics.
Would a <loadop> of DONT_CARE, which makes the PLS contents undefined, be
acceptable in WebGL?
RESOLVED: From a security standpoint, the crucial aspect is that the data
doesn't come from another context, and that needs to be specified. Similar
decisions have been made previously in performance-critical areas of the
spec.
(3) Should we support the ability to enable/disable pixel local storage
planes on an individual basis? (e.g., "LOAD_OP_DISABLE_ANGLE".)
RESOLVED: No. Some implementations need to reserve color attachments for
internal use. Allowing any combination of planes to be enabled or disabled
would make this specification unnecessarily complex. Furthermore, browsers
implementing WebGL will need the ability to interrupt pixel local storage
rendering passes, which would also be more complicated if we were to
support enabling and disabling planes individually.
(4) Should we support binding cube map layers to pixel local storage?
RESOLVED: No. There is currently a 1:1 mapping on every implementation
from pixel local storage shaders to backend shaders, but binding a cube
map layer would require a texelFetch() implementation to behave
differently in the shader. We can always add cube map support in the
future, if the need arises.
(5) Can we support transform feedback?
RESOLVED: No. Transform feedback can lead to render pass breaks in the
Vulkan backend.