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125 lines
3.8 KiB
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125 lines
3.8 KiB
ReStructuredText
Shading Language
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================
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This page describes some tools for working with Mesa's support for the
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`OpenGL Shading Language <https://wikis.khronos.org/opengl/OpenGL_Shading_Language>`__.
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.. _envvars:
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Environment Variables
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---------------------
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The **MESA_GLSL** 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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- **dump** - print GLSL shader code, IR, and NIR to stdout at link time
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- **source** - print GLSL shader code to stdout at link time
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- **log** - log all GLSL shaders to files. The filenames will be
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"shader_X.vert" or "shader_X.frag" where X the shader ID.
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- **cache_info** - print debug information about shader cache
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- **cache_fb** - force cached shaders to be ignored and do a full
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recompile via the fallback path
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- **uniform** - print message to stdout when glUniform is called
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- **nopvert** - force vertex shaders to be a simple shader that just
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transforms the vertex position with ftransform() and passes through
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the color and texcoord[0] attributes.
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- **nopfrag** - force fragment shader to be a simple shader that passes
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through the color attribute.
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- **useprog** - log glUseProgram calls to stderr
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- **errors** - GLSL compilation and link errors will be reported to
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stderr.
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Example: export MESA_GLSL=dump,nopt
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.. _replacement:
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Experimenting with Shader Replacements
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Shaders can be dumped and replaced on runtime for debugging purposes.
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This is controlled via following environment variables:
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- **MESA_SHADER_DUMP_PATH** - path where shader sources are dumped
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- **MESA_SHADER_READ_PATH** - path where replacement shaders are read
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Note, path set must exist before running for dumping or replacing to
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work. When both are set, these paths should be different so the dumped
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shaders do not clobber the replacement shaders. Also, the filenames of
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the replacement shaders should match the filenames of the corresponding
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dumped shaders.
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.. _capture:
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Capturing Shaders
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~~~~~~~~~~~~~~~~~
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Setting **MESA_SHADER_CAPTURE_PATH** to a directory will cause the
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compiler to write ``.shader_test`` files for use with
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`shader-db <https://gitlab.freedesktop.org/mesa/shader-db>`__, a tool
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which compiler developers can use to gather statistics about shaders
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(instructions, cycles, memory accesses, and so on).
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Notably, this captures linked GLSL shaders - with all stages together -
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as well as ARB programs.
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Implementation Notes
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--------------------
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- Shading language programs are compiled first into an AST-related high level
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IR, then into the NIR common shading langauge IR for optimization and
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transformation before going to a backend driver's shader compiler.
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- All function calls are inlined.
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Stand-alone GLSL Compiler
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-------------------------
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The stand-alone GLSL compiler program can be used to compile GLSL
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shaders into GLSL IR code.
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This tool is useful for:
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- Inspecting GLSL frontend behavior to gain insight into compilation
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- Debugging the GLSL compiler itself
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After building Mesa with the ``-Dtools=glsl`` meson option, the compiler will be
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installed as the binary ``glsl_compiler``.
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Here's an example of using the compiler to compile a vertex shader.
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.. code-block:: sh
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src/compiler/glsl/glsl_compiler --version XXX --dump-ast myshader.vert
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Options include
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.. option:: --dump-ast
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dump source syntax tree
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.. option:: --dump-hir
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dump high-level IR code
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.. option:: --dump-lir
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dump low-level IR code
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.. option:: --link
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link shaders
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.. option:: --just-log
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display only shader / linker info if exist, without
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any header or separator
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.. option:: --version
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[Mandatory] define the GLSL version to use
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Compiler Implementation
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-----------------------
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The source code for Mesa's shading language compiler is in the
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``src/compiler/glsl/`` directory.
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