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-<TITLE>Shading Language Support</TITLE>
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+ <h1>The Mesa 3D Graphics Library</h1>
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-
-<H1>Shading Language Support</H1>
+<h1>Shading Language Support</h1>
<p>
This page describes the features and status of Mesa's support for the
-<a href="http://opengl.org/documentation/glsl/" target="_parent">
+<a href="https://opengl.org/documentation/glsl/">
OpenGL Shading Language</a>.
</p>
-<p>
-Last updated on 15 December 2008.
-</p>
-
<p>
Contents
</p>
<ul>
<li><a href="#envvars">Environment variables</a>
-<li><a href="#120">GLSL 1.20 support</a>
+<li><a href="#support">GLSL 1.40 support</a>
<li><a href="#unsup">Unsupported Features</a>
<li><a href="#notes">Implementation Notes</a>
<li><a href="#hints">Programming Hints</a>
</ul>
-
-<a name="envvars">
-<h2>Environment Variables</h2>
+<h2 id="envvars">Environment Variables</h2>
<p>
The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
execution. These are generally used for debugging.
</p>
<ul>
-<li>dump - print GLSL shader code to stdout at link time
-<li>log - log all GLSL shaders to files.
+<li><b>dump</b> - print GLSL shader code to stdout at link time
+<li><b>log</b> - log all GLSL shaders to files.
The filenames will be "shader_X.vert" or "shader_X.frag" where X
the shader ID.
-<li>nopt - disable compiler optimizations
-<li>opt - force compiler optimizations
-<li>uniform - print message to stdout when glUniform is called
-<li>nopvert - force vertex shaders to be a simple shader that just transforms
+<li><b>cache_info</b> - print debug information about shader cache
+<li><b>nopt</b> - disable compiler optimizations
+<li><b>opt</b> - force compiler optimizations
+<li><b>uniform</b> - print message to stdout when glUniform is called
+<li><b>nopvert</b> - force vertex shaders to be a simple shader that just transforms
the vertex position with ftransform() and passes through the color and
texcoord[0] attributes.
-<li>nopfrag - force fragment shader to be a simple shader that passes
+<li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
through the color attribute.
+<li><b>useprog</b> - log glUseProgram calls to stderr
</ul>
<p>
Example: export MESA_GLSL=dump,nopt
</p>
+<p>
+Shaders can be dumped and replaced on runtime for debugging purposes. Mesa
+needs to be configured with '--with-sha1' to enable this functionality. This
+feature is not currently supported by SCons build.
+
+This is controlled via following environment variables:
+<ul>
+<li><b>MESA_SHADER_DUMP_PATH</b> - path where shader sources are dumped
+<li><b>MESA_SHADER_READ_PATH</b> - path where replacement shaders are read
+</ul>
+Note, path set must exist before running for dumping or replacing to work.
+When both are set, these paths should be different so the dumped shaders do
+not clobber the replacement shaders.
+</p>
+
+<h2 id="support">GLSL Version</h2>
-<a name="120">
-<h2>GLSL 1.20 support</h2>
+<p>
+The GLSL compiler currently supports version 3.30 of the shading language.
+</p>
<p>
-GLSL version 1.20 is supported in Mesa 7.3 and later.
-Among the features/differences of GLSL 1.20 are:
+Several GLSL extensions are also supported:
+</p>
<ul>
-<li><code>mat2x3, mat2x4</code>, etc. types and functions
-<li><code>transpose(), outerProduct(), matrixCompMult()</code> functions
-(but untested)
-<li>precision qualifiers (lowp, mediump, highp)
-<li><code>invariant</code> qualifier
-<li><code>array.length()</code> method
-<li><code>float[5] a;</code> array syntax
-<li><code>centroid</code> qualifier
-<li>unsized array constructors
-<li>initializers for uniforms
-<li>const initializers calling built-in functions
+<li>GL_ARB_draw_buffers
+<li>GL_ARB_fragment_coord_conventions
+<li>GL_ARB_shader_bit_encoding
</ul>
+<h2 id="unsup">Unsupported Features</h2>
-<a name="unsup">
-<h2>Unsupported Features</h2>
+<p>XXX update this section</p>
<p>
The following features of the shading language are not yet fully supported
<li>Linking of multiple shaders does not always work. Currently, linking
is implemented through shader concatenation and re-compiling. This
doesn't always work because of some #pragma and preprocessor issues.
-<li>gl_ClipVertex
<li>The gl_Color and gl_SecondaryColor varying vars are interpolated
without perspective correction
</ul>
</p>
-<a name="notes">
-<h2>Implementation Notes</h2>
+<h2 id="notes">Implementation Notes</h2>
<ul>
<li>Shading language programs are compiled into low-level programs
</p>
-<a name="hints">
-<h2>Programming Hints</h2>
+<h2 id="hints">Programming Hints</h2>
<ul>
-<li>Declare <em>in</em> function parameters as <em>const</em> whenever possible.
- This improves the efficiency of function inlining.
-</li>
-<br>
-<li>To reduce register usage, declare variables within smaller scopes.
- For example, the following code:
-<pre>
- void main()
- {
- vec4 a1, a2, b1, b2;
- gl_Position = expression using a1, a2.
- gl_Color = expression using b1, b2;
- }
-</pre>
- Can be rewritten as follows to use half as many registers:
-<pre>
- void main()
- {
- {
- vec4 a1, a2;
- gl_Position = expression using a1, a2.
- }
- {
- vec4 b1, b2;
- gl_Color = expression using b1, b2;
- }
- }
-</pre>
- Alternately, rather than using several float variables, use
- a vec4 instead. Use swizzling and writemasks to access the
- components of the vec4 as floats.
-</li>
-<br>
<li>Use the built-in library functions whenever possible.
For example, instead of writing this:
<pre>
<pre>
float x = inversesqrt(y);
</pre>
-<li>
- Use ++i when possible as it's more efficient than i++
</li>
</ul>
-<a name="standalone">
-<h2>Stand-alone GLSL Compiler</h2>
+<h2 id="standalone">Stand-alone GLSL Compiler</h2>
<p>
-A unique stand-alone GLSL compiler driver has been added to Mesa.
-<p>
-
-<p>
-The stand-alone compiler (like a conventional command-line compiler)
-is a tool that accepts Shading Language programs and emits low-level
-GPU programs.
+The stand-alone GLSL compiler program can be used to compile GLSL shaders
+into low-level GPU code.
</p>
<p>
This tool is useful for:
-<p>
+</p>
<ul>
<li>Inspecting GPU code to gain insight into compilation
<li>Generating initial GPU code for subsequent hand-tuning
</ul>
<p>
-After building Mesa, the glslcompiler can be built by manually running:
+After building Mesa, the compiler can be found at src/compiler/glsl/glsl_compiler
</p>
-<pre>
- make realclean
- make linux
- cd src/mesa/drivers/glslcompiler
- make
-</pre>
-
<p>
Here's an example of using the compiler to compile a vertex shader and
emit GL_ARB_vertex_program-style instructions:
</p>
<pre>
- bin/glslcompiler --debug --numbers --fs progs/glsl/CH06-brick.frag.txt
+ src/compiler/glsl/glsl_compiler --version XXX --dump-ast myshader.vert
</pre>
-<p>
-results in:
-</p>
-<pre>
-# Fragment Program/Shader
- 0: RCP TEMP[4].x, UNIFORM[2].xxxx;
- 1: RCP TEMP[4].y, UNIFORM[2].yyyy;
- 2: MUL TEMP[3].xy, VARYING[0], TEMP[4];
- 3: MOV TEMP[1], TEMP[3];
- 4: MUL TEMP[0].w, TEMP[1].yyyy, CONST[4].xxxx;
- 5: FRC TEMP[1].z, TEMP[0].wwww;
- 6: SGT.C TEMP[0].w, TEMP[1].zzzz, CONST[4].xxxx;
- 7: IF (NE.wwww); # (if false, goto 9);
- 8: ADD TEMP[1].x, TEMP[1].xxxx, CONST[4].xxxx;
- 9: ENDIF;
- 10: FRC TEMP[1].xy, TEMP[1];
- 11: SGT TEMP[2].xy, UNIFORM[3], TEMP[1];
- 12: MUL TEMP[1].z, TEMP[2].xxxx, TEMP[2].yyyy;
- 13: LRP TEMP[0], TEMP[1].zzzz, UNIFORM[0], UNIFORM[1];
- 14: MUL TEMP[0].xyz, TEMP[0], VARYING[1].xxxx;
- 15: MOV OUTPUT[0].xyz, TEMP[0];
- 16: MOV OUTPUT[0].w, CONST[4].yyyy;
- 17: END
-</pre>
-
-<p>
-Note that some shading language constructs (such as uniform and varying
-variables) aren't expressible in ARB or NV-style programs.
-Therefore, the resulting output is not always legal by definition of
-those program languages.
-</p>
-<p>
-Also note that this compiler driver is still under development.
-Over time, the correctness of the GPU programs, with respect to the ARB
-and NV languagues, should improve.
-</p>
+Options include
+<ul>
+<li><b>--dump-ast</b> - dump GPU code
+<li><b>--dump-hir</b> - dump high-level IR code
+<li><b>--dump-lir</b> - dump low-level IR code
+<li><b>--dump-builder</b> - dump GLSL IR code
+<li><b>--link</b> - link shaders
+<li><b>--just-log</b> - display only shader / linker info if exist,
+without any header or separator
+<li><b>--version</b> - [Mandatory] define the GLSL version to use
+</ul>
-<a name="implementation">
-<h2>Compiler Implementation</h2>
+<h2 id="implementation">Compiler Implementation</h2>
<p>
The source code for Mesa's shading language compiler is in the
-<code>src/mesa/shader/slang/</code> directory.
+<code>src/compiler/glsl/</code> directory.
</p>
<p>
-The compiler follows a fairly standard design and basically works as follows:
+XXX provide some info about the compiler....
</p>
-<ul>
-<li>The input string is tokenized (see grammar.c) and parsed
-(see slang_compiler_*.c) to produce an Abstract Syntax Tree (AST).
-The nodes in this tree are slang_operation structures
-(see slang_compile_operation.h).
-The nodes are decorated with symbol table, scoping and datatype information.
-<li>The AST is converted into an Intermediate representation (IR) tree
-(see the slang_codegen.c file).
-The IR nodes represent basic GPU instructions, like add, dot product,
-move, etc.
-The IR tree is mostly a binary tree, but a few nodes have three or four
-children.
-In principle, the IR tree could be executed by doing an in-order traversal.
-<li>The IR tree is traversed in-order to emit code (see slang_emit.c).
-This is also when registers are allocated to store variables and temps.
-<li>In the future, a pattern-matching code generator-generator may be
-used for code generation.
-Programs such as L-BURG (Bottom-Up Rewrite Generator) and Twig look for
-patterns in IR trees, compute weights for subtrees and use the weights
-to select the best instructions to represent the sub-tree.
-<li>The emitted GPU instructions (see prog_instruction.h) are stored in a
-gl_program object (see mtypes.h).
-<li>When a fragment shader and vertex shader are linked (see slang_link.c)
-the varying vars are matched up, uniforms are merged, and vertex
-attributes are resolved (rewriting instructions as needed).
-</ul>
<p>
The final vertex and fragment programs may be interpreted in software
(see drivers/dri/i915/i915_fragprog.c for example).
</p>
-<h3>Code Generation Options</h3>
-
-<p>
-Internally, there are several options that control the compiler's code
-generation and instruction selection.
-These options are seen in the gl_shader_state struct and may be set
-by the device driver to indicate its preferences:
-
-<pre>
-struct gl_shader_state
-{
- ...
- /** Driver-selectable options: */
- GLboolean EmitHighLevelInstructions;
- GLboolean EmitCondCodes;
- GLboolean EmitComments;
-};
-</pre>
-
-<ul>
-<li>EmitHighLevelInstructions
-<br>
-This option controls instruction selection for loops and conditionals.
-If the option is set high-level IF/ELSE/ENDIF, LOOP/ENDLOOP, CONT/BRK
-instructions will be emitted.
-Otherwise, those constructs will be implemented with BRA instructions.
-</li>
-
-<li>EmitCondCodes
-<br>
-If set, condition codes (ala GL_NV_fragment_program) will be used for
-branching and looping.
-Otherwise, ordinary registers will be used (the IF instruction will
-examine the first operand's X component and do the if-part if non-zero).
-This option is only relevant if EmitHighLevelInstructions is set.
-</li>
-
-<li>EmitComments
-<br>
-If set, instructions will be annoted with comments to help with debugging.
-Extra NOP instructions will also be inserted.
-</br>
-
-</ul>
+<h2 id="validation">Compiler Validation</h2>
-
-<a name="validation">
-<h2>Compiler Validation</h2>
-
-<p>
-A <a href="http://glean.sf.net" target="_parent">Glean</a> test has
-been create to exercise the GLSL compiler.
-</p>
<p>
-The <em>glsl1</em> test runs over 170 sub-tests to check that the language
-features and built-in functions work properly.
-This test should be run frequently while working on the compiler to catch
+Developers working on the GLSL compiler should test frequently to avoid
regressions.
</p>
+
<p>
-The test coverage is reasonably broad and complete but additional tests
-should be added.
+The <a href="https://piglit.freedesktop.org/">Piglit</a> project
+has many GLSL tests.
</p>
+<p>
+The Mesa demos repository also has some good GLSL tests.
+</p>
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