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Re: [Public WebGL] Shader validator issue.





On Fri, Aug 20, 2010 at 11:44 AM, <steve@sjbaker.org> wrote:
Oooohhhh...ikky!

So I can't control the LOD of a texture lookup in the frag shader?...Urgh!
 That's a pain in the butt!  There is a significant class of shader
algorithms related to image atlassing that kinda rely on that function.  

texture2D takes an optional bias parameter which you might be able to use depending on what you are trying to do.
 
I
may have to go talk to Microsoft about getting "WebD3D" working! :-)

Oh well, it's a really good thing that the validator works.  I guess I owe
someone my humblest apologies...again!

  -- Steve

> From a bit further up on page 77..
>
>> The built-ins suffixed with "Lod" are allowed only in a vertex
>> shader.
>
> That sounds like the problem :-)
>
>     - Vlad
>
> ----- Original Message -----
>> I think I may have found a validator bug.
>>
>> This shader is boiled down to the bare essentials from a much bigger
>> example...
>>
>> #ifdef GL_ES
>> precision highp float;
>> #endif
>>
>> uniform sampler2D diffuseMap ;
>>
>> void main()
>> {
>> gl_FragColor = texture2DLod ( diffuseMap, vec2(0.5,0.5), 0.0 ) ;
>> }
>>
>> It compiles and runs just fine under last nights' Firefox/Minefield in
>> both Linux & Windows with the validator disabled - but fails with this
>> error with the validator turned on:
>>
>> Error compiling shader:
>> ERROR: 0:10: 'texture2DLod' : no matching overloaded function found
>> ERROR: 0:10: 'assign' : cannot convert from 'const mediump float'
>> to 'FragColor mediump 4-component vector of float'
>> ERROR: 2 compilation errors. No code generated.
>> GL Error: 1281 in loadShaderPairFromString
>>
>> (It also fails in more sane cases, like when the second parameter is a
>> simple varying texCoord and when the third parameter is a float
>> variable).
>>
>> Is there a problem with texture2DLod? I think I'm using it correctly
>> per
>> page 77 of
>> http://www.khronos.org/registry/gles/specs/2.0/GLSL_ES_Specification_1.0.17.pdf
>>
>> It says:
>>
>> vec4 texture2DLod (sampler2D sampler, vec2 coord, float lod)
>>
>> Eh?
>>
>> -- Steve
>>
>>
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