a74300c7ff
For the gallium state tracker a tgsi binary may have been evicted from the cache to make space. In this case we would take the fallback path and recompile/link the shader. On i965 there are a number of reasons we can get to the program upload stage and have neither IR nor a valid cached binary. For example the binary may have been evicted from the cache or we need a variant that wasn't previously cached. This environment variable enables us to force the fallback path that would be taken in these cases and makes it easier to debug these otherwise hard to reproduce scenarios. Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
236 lines
6.4 KiB
HTML
236 lines
6.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html lang="en">
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<head>
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<meta http-equiv="content-type" content="text/html; charset=utf-8">
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<title>Shading Language Support</title>
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<link rel="stylesheet" type="text/css" href="mesa.css">
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</head>
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<body>
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<div class="header">
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<h1>The Mesa 3D Graphics Library</h1>
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</div>
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<iframe src="contents.html"></iframe>
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<div class="content">
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<h1>Shading Language Support</h1>
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<p>
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This page describes the features and status of Mesa's support for the
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<a href="https://opengl.org/documentation/glsl/">
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OpenGL Shading Language</a>.
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</p>
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<p>
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Contents
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</p>
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<ul>
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<li><a href="#envvars">Environment variables</a>
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<li><a href="#support">GLSL 1.40 support</a>
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<li><a href="#unsup">Unsupported Features</a>
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<li><a href="#notes">Implementation Notes</a>
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<li><a href="#hints">Programming Hints</a>
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<li><a href="#standalone">Stand-alone GLSL Compiler</a>
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<li><a href="#implementation">Compiler Implementation</a>
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<li><a href="#validation">Compiler Validation</a>
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</ul>
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<h2 id="envvars">Environment Variables</h2>
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<p>
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The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
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list of keywords to control some aspects of the GLSL compiler and shader
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execution. These are generally used for debugging.
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</p>
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<ul>
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<li><b>dump</b> - print GLSL shader code to stdout at link time
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<li><b>log</b> - log all GLSL shaders to files.
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The filenames will be "shader_X.vert" or "shader_X.frag" where X
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the shader ID.
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<li><b>cache_info</b> - print debug information about shader cache
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<li><b>cache_fb</b> - force cached shaders to be ignored and do a full
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recompile via the fallback path</li>
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<li><b>uniform</b> - print message to stdout when glUniform is called
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<li><b>nopvert</b> - force vertex shaders to be a simple shader that just transforms
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the vertex position with ftransform() and passes through the color and
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texcoord[0] attributes.
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<li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
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through the color attribute.
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<li><b>useprog</b> - log glUseProgram calls to stderr
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</ul>
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<p>
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Example: export MESA_GLSL=dump,nopt
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</p>
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<p>
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Shaders can be dumped and replaced on runtime for debugging purposes. Mesa
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needs to be configured with '--with-sha1' to enable this functionality. This
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feature is not currently supported by SCons build.
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This is controlled via following environment variables:
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<ul>
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<li><b>MESA_SHADER_DUMP_PATH</b> - path where shader sources are dumped
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<li><b>MESA_SHADER_READ_PATH</b> - path where replacement shaders are read
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</ul>
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Note, path set must exist before running for dumping or replacing to work.
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When both are set, these paths should be different so the dumped shaders do
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not clobber the replacement shaders.
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</p>
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<h2 id="support">GLSL Version</h2>
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<p>
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The GLSL compiler currently supports version 3.30 of the shading language.
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</p>
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<p>
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Several GLSL extensions are also supported:
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</p>
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<ul>
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<li>GL_ARB_draw_buffers
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<li>GL_ARB_fragment_coord_conventions
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<li>GL_ARB_shader_bit_encoding
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</ul>
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<h2 id="unsup">Unsupported Features</h2>
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<p>XXX update this section</p>
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<p>
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The following features of the shading language are not yet fully supported
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in Mesa:
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</p>
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<ul>
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<li>Linking of multiple shaders does not always work. Currently, linking
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is implemented through shader concatenation and re-compiling. This
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doesn't always work because of some #pragma and preprocessor issues.
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<li>The gl_Color and gl_SecondaryColor varying vars are interpolated
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without perspective correction
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</ul>
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<p>
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All other major features of the shading language should function.
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</p>
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<h2 id="notes">Implementation Notes</h2>
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<ul>
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<li>Shading language programs are compiled into low-level programs
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very similar to those of GL_ARB_vertex/fragment_program.
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<li>All vector types (vec2, vec3, vec4, bvec2, etc) currently occupy full
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float[4] registers.
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<li>Float constants and variables are packed so that up to four floats
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can occupy one program parameter/register.
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<li>All function calls are inlined.
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<li>Shaders which use too many registers will not compile.
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<li>The quality of generated code is pretty good, register usage is fair.
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<li>Shader error detection and reporting of errors (InfoLog) is not
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very good yet.
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<li>The ftransform() function doesn't necessarily match the results of
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fixed-function transformation.
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</ul>
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<p>
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These issues will be addressed/resolved in the future.
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</p>
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<h2 id="hints">Programming Hints</h2>
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<ul>
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<li>Use the built-in library functions whenever possible.
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For example, instead of writing this:
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<pre>
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float x = 1.0 / sqrt(y);
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</pre>
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Write this:
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<pre>
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float x = inversesqrt(y);
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</pre>
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</li>
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</ul>
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<h2 id="standalone">Stand-alone GLSL Compiler</h2>
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<p>
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The stand-alone GLSL compiler program can be used to compile GLSL shaders
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into low-level GPU code.
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</p>
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<p>
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This tool is useful for:
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</p>
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<ul>
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<li>Inspecting GPU code to gain insight into compilation
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<li>Generating initial GPU code for subsequent hand-tuning
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<li>Debugging the GLSL compiler itself
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</ul>
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<p>
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After building Mesa, the compiler can be found at src/compiler/glsl/glsl_compiler
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</p>
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<p>
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Here's an example of using the compiler to compile a vertex shader and
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emit GL_ARB_vertex_program-style instructions:
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</p>
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<pre>
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src/compiler/glsl/glsl_compiler --version XXX --dump-ast myshader.vert
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</pre>
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Options include
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<ul>
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<li><b>--dump-ast</b> - dump GPU code
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<li><b>--dump-hir</b> - dump high-level IR code
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<li><b>--dump-lir</b> - dump low-level IR code
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<li><b>--dump-builder</b> - dump GLSL IR code
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<li><b>--link</b> - link shaders
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<li><b>--just-log</b> - display only shader / linker info if exist,
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without any header or separator
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<li><b>--version</b> - [Mandatory] define the GLSL version to use
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</ul>
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<h2 id="implementation">Compiler Implementation</h2>
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<p>
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The source code for Mesa's shading language compiler is in the
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<code>src/compiler/glsl/</code> directory.
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</p>
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<p>
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XXX provide some info about the compiler....
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</p>
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<p>
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The final vertex and fragment programs may be interpreted in software
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(see prog_execute.c) or translated into a specific hardware architecture
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(see drivers/dri/i915/i915_fragprog.c for example).
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</p>
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<h2 id="validation">Compiler Validation</h2>
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<p>
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Developers working on the GLSL compiler should test frequently to avoid
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regressions.
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</p>
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<p>
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The <a href="https://piglit.freedesktop.org/">Piglit</a> project
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has many GLSL tests.
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</p>
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<p>
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The Mesa demos repository also has some good GLSL tests.
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</p>
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</div>
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</body>
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</html>
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