-Last updated on 28 March 2007. -
-Contents
+The MESA_GLSL 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. +
++Example: export MESA_GLSL=dump,nopt +
+ + + ++The GLSL compiler currently supports version 1.20 of the shading language. +
+ ++Several GLSL extensions are also supported: +
+XXX update this section
+-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:
@@ -67,7 +115,6 @@ All other major features of the shading language should function.
- void main()
- {
- vec4 a1, a2, b1, b2;
- gl_Position = expression using a1, a2.
- gl_Color = expression using b1, b2;
- }
-
- Can be rewritten as follows to use half as many registers:
-
- void main()
- {
- {
- vec4 a1, a2;
- gl_Position = expression using a1, a2.
- }
- {
- vec4 b1, b2;
- gl_Color = expression using b1, b2;
- }
- }
-
- Alternately, rather than using several float variables, use
- a vec4 instead. Use swizzling and writemasks to access the
- components of the vec4 as floats.
-
@@ -123,23 +137,16 @@ These issues will be addressed/resolved in the future.
float x = inversesqrt(y);
--A unique stand-alone GLSL compiler driver has been added to Mesa. -
+
-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.
@@ -152,48 +159,25 @@ This tool is useful for:
-To build the glslcompiler program (this will be improved someday): +After building Mesa, the compiler can be found at src/glsl/glsl_compiler
-- cd src/mesa - make libmesa.a - cd drivers/glslcompiler - make --
Here's an example of using the compiler to compile a vertex shader and emit GL_ARB_vertex_program-style instructions:
- glslcompiler --arb --linenumbers --vs vertshader.txt --
-The output may look similar to this: -
--!!ARBvp1.0 - 0: MOV result.texcoord[0], vertex.texcoord[0]; - 1: DP4 temp0.x, state.matrix.mvp.row[0], vertex.position; - 2: DP4 temp0.y, state.matrix.mvp.row[1], vertex.position; - 3: DP4 temp0.z, state.matrix.mvp.row[2], vertex.position; - 4: DP4 temp0.w, state.matrix.mvp.row[3], vertex.position; - 5: MOV result.position, temp0; - 6: END + src/glsl/glsl_compiler --dump-ast myshader.vert-
-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. -
--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. -
+Options include +
The source code for Mesa's shading language compiler is in the
-src/mesa/shader/slang/ directory.
+src/glsl/ directory.
-The compiler follows a fairly standard design and basically works as follows: +XXX provide some info about the compiler....
-The final vertex and fragment programs may be interpreted in software @@ -291,20 +249,20 @@ Extra NOP instructions will also be inserted.
-A new Glean test has -been create to exercise the GLSL compiler. -
--The glsl1 test runs over 150 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.
+-The test coverage is reasonably broad and complete but additional tests -should be added. +The Piglit project +has many GLSL tests and the +Glean glsl1 test +tests GLSL features.
++The Mesa demos repository also has some good GLSL tests. +