diff options
Diffstat (limited to 'docs/specs/EXT_shader_samples_identical.txt')
| -rw-r--r-- | docs/specs/EXT_shader_samples_identical.txt | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/docs/specs/EXT_shader_samples_identical.txt b/docs/specs/EXT_shader_samples_identical.txt new file mode 100644 index 00000000000..a8a901b8bbd --- /dev/null +++ b/docs/specs/EXT_shader_samples_identical.txt @@ -0,0 +1,176 @@ +Name + + EXT_shader_samples_identical + +Name Strings + + GL_EXT_shader_samples_identical + +Contact + + Ian Romanick, Intel (ian.d.romanick 'at' intel.com) + +Contributors + + Chris Forbes, Mesa + Magnus Wendt, Intel + Neil S. Roberts, Intel + Graham Sellers, AMD + +Status + + XXX - Not complete yet. + +Version + + Last Modified Date: November 19, 2015 + Revision: 6 + +Number + + TBD + +Dependencies + + OpenGL 3.2, or OpenGL ES 3.1, or ARB_texture_multisample is required. + + This extension is written against the OpenGL 4.5 (Core Profile) + Specification + +Overview + + Multisampled antialiasing has become a common method for improving the + quality of rendered images. Multisampling differs from supersampling in + that the color of a primitive that covers all or part of a pixel is + resolved once, regardless of the number of samples covered. If a large + polygon is rendered, the colors of all samples in each interior pixel will + be the same. This suggests a simple compression scheme that can reduce + the necessary memory bandwidth requirements. In one such scheme, each + sample is stored in a separate slice of the multisample surface. An + additional multisample control surface (MCS) contains a mapping from pixel + samples to slices. + + If all the values stored in the MCS for a particular pixel are the same, + then all the samples have the same value. Applications can take advantage + of this information to reduce the bandwidth of reading multisample + textures. A custom multisample resolve filter could optimize resolving + pixels where every sample is identical by reading the color once. + + color = texelFetch(sampler, coordinate, 0); + if (!textureSamplesIdenticalEXT(sampler, coordinate)) { + for (int i = 1; i < MAX_SAMPLES; i++) { + vec4 c = texelFetch(sampler, coordinate, i); + + //... accumulate c into color + + } + } + +New Procedures and Functions + + None. + +New Tokens + + None. + +Additions to the OpenGL 4.5 (Core Profile) Specification + + None. + +Modifications to The OpenGL Shading Language Specification, Version 4.50.5 + + Including the following line in a shader can be used to control the + language features described in this extension: + + #extension GL_EXT_shader_samples_identical + + A new preprocessor #define is added to the OpenGL Shading Language: + + #define GL_EXT_shader_samples_identical + + Add to the table in section 8.7 "Texture Lookup Functions" + + Syntax: + + bool textureSamplesIdenticalEXT(gsampler2DMS sampler, ivec2 coord) + + bool textureSamplesIdenticalEXT(gsampler2DMSArray sampler, + ivec3 coord) + + Description: + + Returns true if it can be determined that all samples within the texel + of the multisample texture bound to <sampler> at <coord> contain the + same values or false if this cannot be determined." + +Additions to the AGL/EGL/GLX/WGL Specifications + + None + +Errors + + None + +New State + + None + +New Implementation Dependent State + + None + +Issues + + 1) What should the new functions be called? + + RESOLVED: textureSamplesIdenticalEXT. Initially + textureAllSamplesIdenticalEXT was considered, but + textureSamplesIdenticalEXT is more similar to the existing textureSamples + function. + + 2) It seems like applications could implement additional optimization if + they were provided with raw MCS data. Should this extension also + provide that data? + + There are a number of challenges in providing raw MCS data. The biggest + problem being that the amount of MCS data depends on the number of + samples, and that is not known at compile time. Additionally, without new + texelFetch functions, applications would have difficulty utilizing the + information. + + Another option is to have a function that returns an array of tuples of + sample number and count. This also has difficulties with the maximum + array size not being known at compile time. + + RESOLVED: Do not expose raw MCS data in this extension. + + 3) Should this extension also extend SPIR-V? + + RESOLVED: Yes, but this has not yet been written. + + 4) Is it possible for textureSamplesIdenticalEXT to report false negatives? + + RESOLVED: Yes. It is possible that the underlying hardware may not detect + that separate writes of the same color to different samples of a pixel are + the same. The shader function is at the whim of the underlying hardware + implementation. It is also possible that a compressed multisample surface + is not used. In that case the function will likely always return false. + +Revision History + + Rev Date Author Changes + --- ---------- -------- --------------------------------------------- + 1 2014/08/20 cforbes Initial version + 2 2015/10/23 idr Change from MESA to EXT. Rebase on OpenGL 4.5, + and add dependency on OpenGL ES 3.1. Initial + draft of overview section and issues 1 through + 3. + 3 2015/10/27 idr Typo fixes. + 4 2015/11/10 idr Rename extension from EXT_shader_multisample_compression + to EXT_shader_samples_identical. + Add issue #4. + 5 2015/11/18 idr Fix some typos spotted by gsellers. Change the + name of the name of the function to + textureSamplesIdenticalEXT. + 6 2015/11/19 idr Fix more typos spotted by Nicolai Hähnle. |