</p>
<p>
-Last updated on 20 Jan 2007.
+Contents
+</p>
+<ul>
+<li><a href="#envvars">Environment variables</a>
+<li><a href="#120">GLSL 1.20 support</a>
+<li><a href="#unsup">Unsupported Features</a>
+<li><a href="#notes">Implementation Notes</a>
+<li><a href="#hints">Programming Hints</a>
+<li><a href="#standalone">Stand-alone GLSL Compiler</a>
+<li><a href="#implementation">Compiler Implementation</a>
+<li><a href="#validation">Compiler Validation</a>
+</ul>
+
+
+
+<a name="envvars">
+<h2>Environment Variables</h2>
+
+<p>
+The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
+list of keywords to control some aspects of the GLSL compiler and shader
+execution. These are generally used for debugging.
+</p>
+<ul>
+<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><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><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>
+
+<a name="120">
+<h2>GLSL Version</h2>
+
+<p>
+The GLSL compiler currently supports version 1.20 of the shading language.
+</p>
+
+<p>
+Several GLSL extensions are also supported:
+</p>
+<ul>
+<li>GL_ARB_draw_buffers
+<li>GL_ARB_texture_rectangle
+<li>GL_ARB_fragment_coord_conventions
+<li>GL_EXT_texture_array
+</ul>
+
+
+<a name="unsup">
<h2>Unsupported Features</h2>
+<p>XXX update this section</p>
+
<p>
-The following features of the shading language are not yet supported
+The following features of the shading language are not yet fully supported
in Mesa:
</p>
<ul>
-<li>Arrays
-<li>Structs
-<li>Linking of multiple shaders is not supported
-<li>Not all built-in OpenGL state variables are supported yet.
- Common variables such as gl_ModelViewMatrix and gl_NormalMatrix
- are supported.
-<li>Integer operations are not fully implemented (most are implemented
- as floating point).
+<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>
</p>
+<a name="notes">
<h2>Implementation Notes</h2>
<ul>
<li>The quality of generated code is pretty good, register usage is fair.
<li>Shader error detection and reporting of errors (InfoLog) is not
very good yet.
-<li>There are massive memory leaks in the compiler.
+<li>The ftransform() function doesn't necessarily match the results of
+ fixed-function transformation.
</ul>
<p>
</p>
+<a name="hints">
<h2>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>
+</ul>
+
+
+<a name="standalone">
+<h2>Stand-alone GLSL Compiler</h2>
+
+<p>
+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>
+<ul>
+<li>Inspecting GPU code to gain insight into compilation
+<li>Generating initial GPU code for subsequent hand-tuning
+<li>Debugging the GLSL compiler itself
+</ul>
+
+<p>
+After building Mesa, the compiler can be found at src/glsl/glsl_compiler
+</p>
+
+<p>
+Here's an example of using the compiler to compile a vertex shader and
+emit GL_ARB_vertex_program-style instructions:
+</p>
+<pre>
+ src/glsl/glslcompiler --dump-ast myshader.vert
+</pre>
+
+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>--link</b> - ???
</ul>
+
+
+<a name="implementation">
+<h2>Compiler Implementation</h2>
+
+<p>
+The source code for Mesa's shading language compiler is in the
+<code>src/glsl/</code> directory.
+</p>
+
+<p>
+XXX provide some info about the compiler....
+</p>
+
+<p>
+The final vertex and fragment programs may be interpreted in software
+(see prog_execute.c) or translated into a specific hardware architecture
+(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>
+
+
+<a name="validation">
+<h2>Compiler Validation</h2>
+
+<p>
+Developers working on the GLSL compiler should test frequently to avoid
+regressions.
+</p>
+
+<p>
+The <a href="http://people.freedesktop.org/~nh/piglit/">Piglit</a> project
+has many GLSL tests and the
+<a href="http://glean.sf.net" target="_parent">Glean</a> glsl1 test
+tests GLSL features.
+</p>
+
+<p>
+The Mesa demos repository also has some good GLSL tests.
+</p>
+
</BODY>
</HTML>
projects / mesa.git / blobdiff