[Mesa-dev] how mesa glsl compiler generate ir_texture

[Kenneth Graunke]

On 08/22/2013 02:59 AM, Liu Xin wrote:
> Dear list,
>
> i wonder if all vendors in mesa3d use intel's glsl compiler now? by
> browsing glsl source code, i still don't understand how it generates
> ir_texture.  in my idea, it treats it as normal function call.

Yes, all drivers use the same shader compiler, in src/glsl.

> for example, this is tiny fragment shader:
> uniform sampler2D sampler2d;
> varying mediump vec2  myTexCoord;
> void main (void)
> {
>    gl_FragColor = texture2D(sampler2d,myTexCoord);
> }
>
> glsl_compiler will emit LIR/HIR like this. please note (call texture2D
> ...). it's a normal ir_call instead of ir_texture.  i confirm that
> ast2hir doesn't new ir_texture in any case.

That's correct.  At shader compile time, all built-in functions 
(texturing, mix, abs, sin, etc.) are treated as normal functions.

We create several other shaders - stored in the builtins_to_link list - 
and at link time, we link those with the user's shaders.  Then, the 
function inliner runs and replaces the (call ...) nodes.

If you run ./src/glsl/builtins/tools/texture_builtins.py, you can see 
the IR for all of the texturing functions.  The body of these functions 
contain the (tex ...) nodes.  ir_reader creates these, as part of 
_mesa_glsl_initialize_functions().

The built-in code is kind of a mess...sorry for that.

> (function main
>    (signature void
>      (parameters
>      )
>      (
>        (declare (temporary ) vec4 texture2D_retval at 0x94fc11c)
>        (assign (constant bool (1)) (xyzw) (var_ref
> texture2D_retval at 0x94fc11c)  (call texture2D ((var_ref
> sampler2d at 0x955b114) (var_ref myTexCoord at 0x955b03c) ))
> )
>        (assign (constant bool (1)) (xyzw) (var_ref
> gl_FragColor at 0x92c2eb4)  (var_ref texture2D_retval at 0x94fc11c) )
>      ))
>
> )
>
> do mesa glsl compiler can make use of ir_texture? i think it must be yes
> because all GPUs have texture unit and should handle tex commands. how
> does mesa do it?
>
> thanks,
> --lx
>
>
>
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