Commit f3ec111b authored by Brian Paul's avatar Brian Paul

docs: updated info about GLSL compiler

Ian or Eric should review this and add/edit as needed.
parent 484dde2d
......@@ -39,19 +39,19 @@ list of keywords to control some aspects of the GLSL compiler and shader
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>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>useprog - log glUseProgram calls to stderr
<li><b>useprog</b> - log glUseProgram calls to stderr
</ul>
<p>
Example: export MESA_GLSL=dump,nopt
......@@ -59,30 +59,28 @@ Example: export MESA_GLSL=dump,nopt
<a name="120">
<h2>GLSL 1.20 support</h2>
<h2>GLSL Version</h2>
<p>
GLSL version 1.20 is supported in Mesa 7.3 and later.
Among the features/differences of GLSL 1.20 are:
The GLSL compiler currently supports version 1.20 of the shading language.
</p>
<p>
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_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 fully supported
in Mesa:
......@@ -130,39 +128,6 @@ These issues will be addressed/resolved in the future.
<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>
......@@ -172,8 +137,6 @@ These issues will be addressed/resolved in the future.
<pre>
float x = inversesqrt(y);
</pre>
<li>
Use ++i when possible as it's more efficient than i++
</li>
</ul>
......@@ -182,13 +145,8 @@ These issues will be addressed/resolved in the future.
<h2>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>
......@@ -201,59 +159,25 @@ This tool is useful for:
</ul>
<p>
After building Mesa, the glslcompiler can be built by manually running:
After building Mesa, the compiler can be found at src/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
</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
src/glsl/glslcompiler --dump-ast myshader.vert
</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>--link</b> - ???
</ul>
......@@ -262,38 +186,12 @@ and NV languagues, should improve.
<p>
The source code for Mesa's shading language compiler is in the
<code>src/mesa/shader/slang/</code> directory.
<code>src/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
......@@ -351,20 +249,20 @@ Extra NOP instructions will also be inserted.
<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="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>
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