[Mesa-dev] how mesa glsl compiler generate ir_texture

[Liu Xin]

Kenneth,

thank you for your guide. mesa code is much clearer for me now.

--lx


On 08/23/2013 02:07 AM, Kenneth Graunke wrote:
> 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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>