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texture look-up using ATI_fragment_shader

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Greetings, I'm trying to implement a texture-palette using ATI_fragment_shader. I have a new FireGL card. For testing, I amd trying to apply a 256-entry look-up table to a GL_UNSIGNED_BYTE luminance 2D texture. All I get is a blank display, when I enable the shader. I'd appreaciate any suggestions. I've included my code below: GLuint nTex, nPalette; // dependent texture glGenTextures(1, &nTex); glActiveTextureARB( GL_TEXTURE0_ARB); glBindTexture( GL_TEXTURE_2D, nTex); unsigned char pSlice[256*256], *ptr; ptr = pSlice; for(int i=0; i<256; ++i) { memset(ptr, i, 256); ptr += 256; } glTexImage2D( GL_TEXTURE_2D, // target 0, // level 1, // internal format 256, // width 256, // height 0, // border GL_LUMINANCE, // format GL_UNSIGNED_BYTE, // type (void*) pSlice ); // texture palette glGenTextures(1, &nPalette); glActiveTextureARB( GL_TEXTURE1_ARB); glBindTexture( GL_TEXTURE_2D, nPalette ); float pfLUT[256*4], *pPtr; pPtr = pfLUT; for(int l=0; l<256; ++l) { pPtr[0] = l < 128 ? 0.0 : 1.0; pPtr[1] = pPtr[2] = pPtr[3] = 1.0; pPtr += 4; } glTexImage2D( GL_TEXTURE_2D, // target 0, // level 4, // internal format 256, // width 1, // height 0, // border GL_RGBA, // format GL_FLOAT, // type (void*) pfLUT ); simpleFragmentShader = glGenFragmentShadersATI(1); glBindFragmentShaderATI (simpleFragmentShader); glBeginFragmentShaderATI(); glSampleMapATI ( GL_REG_0_ATI, GL_TEXTURE0_ARB, GL_SWIZZLE_STR_ATI); glPassTexCoordATI(GL_REG_0_ATI, GL_REG_0_ATI, GL_SWIZZLE_STR_ATI); // dummy operation to end the first pass (better way ?) glColorFragmentOp1ATI (GL_MOV_ATI, GL_REG_2_ATI, GL_NONE, GL_NONE, GL_REG_3_ATI, GL_NONE, GL_NONE); // Dependent texture read glSampleMapATI ( GL_REG_1_ATI, GL_REG_0_ATI, GL_SWIZZLE_STR_ATI); glColorFragmentOp1ATI (GL_MOV_ATI, GL_REG_0_ATI, GL_NONE, GL_NONE, GL_REG_1_ATI, GL_NONE, GL_NONE); glEndFragmentShaderATI();

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