On Wednesday, November 18, 2015 03:46:47 PM Ian Romanick wrote:
> From: Ian Romanick <ian.d.roman...@intel.com>
>
> Signed-off-by: Ian Romanick <ian.d.roman...@intel.com>
> Cc: "Chris Forbes" <chr...@ijw.co.nz>
> ---
> docs/specs/EXT_shader_samples_identical.txt | 174
> ++++++++++++++++++++++++++++
> 1 file changed, 174 insertions(+)
> create mode 100644 docs/specs/EXT_shader_samples_identical.txt
>
> diff --git a/docs/specs/EXT_shader_samples_identical.txt
> b/docs/specs/EXT_shader_samples_identical.txt
> new file mode 100644
> index 0000000..bae6c73
> --- /dev/null
> +++ b/docs/specs/EXT_shader_samples_identical.txt
> @@ -0,0 +1,174 @@
> +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
> + Graham Sellers, AMD
> +
> +Status
> +
> + XXX - Not complete yet.
> +
> +Version
> +
> + Last Modified Date: November 18, 2015
> + Revision: 5
> +
> +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 (!textureSamplesAllIdenticalEXT(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 textureSamplesAllIdenticalEXT 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.Might it be worth adding an issue about ARB_image_load_store? 5) Should this extension offer similar functionality for images, in addition to textures? RESOLVED: Not in this extension. Just a thought, since some of the other "number of samples" extensions included images. Up to you - not a big deal either way. > + > +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. >
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