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glsl: change uniform location/offset encoding

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This lets Mesa work like other OpenGL implementations with regard
to indexing uniform arrays.  See comments for details.

This is a combination of commits 5d0e136eff
and 1bbf803e3b from master which didn't
apply cleanly with git cherry-pick.
This commit is contained in:
Brian Paul 2010-06-08 08:43:37 -06:00
parent d2f2d0a1b7
commit 7dbfc2565e
1 changed files with 54 additions and 25 deletions
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79
src/mesa/shader/shader_api.c
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@ -1259,6 +1259,54 @@ lookup_uniform_parameter(GLcontext *ctx, GLuint program, GLint location,
}
/**
* GLGL uniform arrays and structs require special handling.
*
* The GL_ARB_shader_objects spec says that if you use
* glGetUniformLocation to get the location of an array, you CANNOT
* access other elements of the array by adding an offset to the
* returned location. For example, you must call
* glGetUniformLocation("foo[16]") if you want to set the 16th element
* of the array with glUniform().
*
* HOWEVER, some other OpenGL drivers allow accessing array elements
* by adding an offset to the returned array location. And some apps
* seem to depend on that behaviour.
*
* Mesa's gl_uniform_list doesn't directly support this since each
* entry in the list describes one uniform variable, not one uniform
* element. We could insert dummy entries in the list for each array
* element after [0] but that causes complications elsewhere.
*
* We solve this problem by encoding two values in the location that's
* returned by glGetUniformLocation():
* a) index into gl_uniform_list::Uniforms[] for the uniform
* b) an array/field offset (0 for simple types)
*
* These two values are encoded in the high and low halves of a GLint.
* By putting the uniform number in the high part and the offset in the
* low part, we can support the unofficial ability to index into arrays
* by adding offsets to the location value.
*/
static void
merge_location_offset(GLint *location, GLint offset)
{
*location = (*location << 16) | offset;
}
/**
* Seperate the uniform location and parameter offset. See above.
*/
static void
split_location_offset(GLint *location, GLint *offset)
{
*offset = *location & 0xffff;
*location = *location >> 16;
}
/**
* Called via ctx->Driver.GetUniformfv().
*/
@ -1268,6 +1316,9 @@ _mesa_get_uniformfv(GLcontext *ctx, GLuint program, GLint location,
{
struct gl_program *prog;
GLint paramPos;
GLint offset;
split_location_offset(&location, &offset);
lookup_uniform_parameter(ctx, program, location, &prog, &paramPos);
@ -1298,7 +1349,10 @@ _mesa_get_uniformiv(GLcontext *ctx, GLuint program, GLint location,
{
struct gl_program *prog;
GLint paramPos;
GLint offset;
split_location_offset(&location, &offset);
lookup_uniform_parameter(ctx, program, location, &prog, &paramPos);
if (prog) {
@ -1318,31 +1372,6 @@ _mesa_get_uniformiv(GLcontext *ctx, GLuint program, GLint location,
}
/**
* The value returned by GetUniformLocation actually encodes two things:
* 1. the index into the prog->Uniforms[] array for the uniform
* 2. an offset in the prog->ParameterValues[] array for specifying array
* elements or structure fields.
* This function merges those two values.
*/
static void
merge_location_offset(GLint *location, GLint offset)
{
*location = *location | (offset << 16);
}
/**
* Seperate the uniform location and parameter offset. See above.
*/
static void
split_location_offset(GLint *location, GLint *offset)
{
*offset = (*location >> 16);
*location = *location & 0xffff;
}
/**
* Called via ctx->Driver.GetUniformLocation().
*