kc3-lang/angle/extensions/ANGLE_shader_pixel_local_storage.txt
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Hash : eb1a13d8
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Date : 2022-12-06T21:56:42
Improve PLS load and store op tokens Define more new tokens that are more clearly named, as opposed to recycling tokens that were meant for a different purpose. Bug: angleproject:7279 Change-Id: I840e5ea168235c49eec2693b2231c2d329027b0e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4082057 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org>
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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 GL_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[4]) void BeginPixelLocalStorageANGLE(sizei n, const enum loadops[]) void EndPixelLocalStorageANGLE(sizei n, const enum storeops[]) void PixelLocalStorageBarrierANGLE() void GetFramebufferPixelLocalStorageParameter{f,i}vANGLE(int plane, enum pname, 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 LOAD_OP_DISABLE_ANGLE 0x96E7 Accepted as array elements in the <storeops> parameter of EndPixelLocalStorageANGLE(): STORE_OP_STORE_ANGLE 0x96E8 Accepted by the <pname> parameter of GetFramebufferPixelLocalStorageParameterivANGLE(): PIXEL_LOCAL_FORMAT_ANGLE 0x96E9 PIXEL_LOCAL_TEXTURE_NAME_ANGLE 0x96EA PIXEL_LOCAL_TEXTURE_LEVEL_ANGLE 0x96EB PIXEL_LOCAL_TEXTURE_LAYER_ANGLE 0x96EC Accepted by the <pname> parameter of GetFramebufferPixelLocalStorageParameterfvANGLE(): PIXEL_LOCAL_CLEAR_VALUE_FLOAT_ANGLE 0x96ED Accepted by the <pname> parameter of GetFramebufferPixelLocalStorageParameterivANGLE(): PIXEL_LOCAL_CLEAR_VALUE_INT_ANGLE 0x96EE PIXEL_LOCAL_CLEAR_VALUE_UNSIGNED_INT_ANGLE 0x96EF 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. LOAD_OP_DISABLE_ANGLE Leave this plane disabled. Note that all pixel local storage planes on or after index <n> are disabled implicitly. 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 or disabled. 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_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 SAMPLE_ALPHA_TO_COVERAGE is enabled. * INVALID_OPERATION is generated if SAMPLE_COVERAGE is enabled. * 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 <loadops>[0..<n>-1] is not LOAD_OP_DISABLE_ANGLE, and the pixel local storage plane at that same index 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_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] (except those whose Load Operation was LOAD_OP_DISABLE_ANGLE) 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 DepthMask MapBufferRange BindBuffer DepthRangef PixelLocalStorageBarrierANGLE BindBufferBase Disable SamplerParameter* BindBufferRange DisableVertexAttribArray Scissor BindSampler Disablei* StencilFunc BindTexture DispatchComputeIndirect StencilFuncSeparate BindVertexArray DrawArrays* StencilMask BlendEquationSeparatei* DrawElements* StencilMaskSeparate BlendEquationi* DrawRangeElements* StencilOp BlendFuncSeparatei* Enable StencilOpSeparate BlendFunci* EnableClientState TexParameter* BufferData EnableVertexAttribArray Uniform* BufferSubData Enablei* UnmapBuffer CheckFramebufferStatus EndPixelLocalStorageANGLE UseProgram ClearBuffer* FrontFace ValidateProgram ColorMaski* Get* VertexAttrib* CullFace Is* DepthFunc 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, DEPTH_TEST, POLYGON_OFFSET_FILL, PRIMITIVE_RESTART_FIXED_INDEX, SCISSOR_TEST, STENCIL_TEST * INVALID_OPERATION is generated by ClearBufferfv(), ClearBufferiv(), ClearBufferuiv() if <buffer> is COLOR and: <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: <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: <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 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_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. Modify Section 4.4.2 "Attaching Images to Framebuffer Objects" (Insert two new numbered section after 4.4.2.3 "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_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 Cube Map Face to bind if <backingtexture> is a TEXTURE_CUBE_MAP, as enumerated in Table X.4 <layer> Cube Map Face -------------------------------------- 0 TEXTURE_CUBE_MAP_POSITIVE_X 1 TEXTURE_CUBE_MAP_NEGATIVE_X 2 TEXTURE_CUBE_MAP_POSITIVE_Y 3 TEXTURE_CUBE_MAP_NEGATIVE_Y 4 TEXTURE_CUBE_MAP_POSITIVE_Z 5 TEXTURE_CUBE_MAP_NEGATIVE_Z Table X.4: <layer> numbers of cube map texture faces. The layers are numbered in the same sequence as the cube map face token values. - 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_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_ENUM is generated if <backingtexture> is nonzero and not of type TEXTURE_2D, TEXTURE_CUBE_MAP, 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 was bound is automatically converted to a memoryless plane of matching internalformat. 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[4]) void FramebufferPixelLocalClearValueivANGLE(int plane, const int value[4]) void FramebufferPixelLocalClearValueuivANGLE(int plane, const uint value[4]) 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_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, float* params) void GetFramebufferPixelLocalStorageParameterivANGLE(int plane, enum pname, int* params) Parameters: * <plane> identifies the pixel local storage plane index. * <pname> specifies the parameter of the plane to query. * <params> returns the value parameter <pname> for the plane. 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_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. 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 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. 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 EndPixelLocalStorageANGLE() before handing off control to the other virtual context, and BeginPixelLocalStorageANGLE() 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.