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The fixed-function pipeline consisted of a series of stages that transformed geometry data into pixels. One of these stages was the texturing stage, which was responsible for applying textures to the geometry to create the final appearance of the object. Before ARB_texture_env_combine, there were only a few basic operations available to combine textures, such as modulate and blend.
ARB_texture_env_combine introduced a more flexible set of operations and operands, allowing developers to create more complex texture blending operations. The extension added new environment modes and allowed textures to be combined using arithmetic operations such as ADD, SUBTRACT, INTERPOLATE, and others.
Here's a general breakdown of how ARB_texture_env_combine works:
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB);
glTexEnvf(GL_TEXTURE_ENV, GL_COMBINE_RGB_ARB, GL_<COMBINE_OPERATION>);
glTexEnvf(GL_TEXTURE_ENV, GL_COMBINE_ALPHA_ARB, GL_<COMBINE_OPERATION>);
Replace <COMBINE_OPERATION> with the desired operation, such as GL_ADD, GL_SUBTRACT, or GL_INTERPOLATE.
3. Set the source and operand: For each texture unit, you need to specify the source and operand for the RGB and alpha channels. This can be done using glTexEnvi:
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB_ARB, GL_<SOURCE>);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB_ARB, GL_<OPERAND>);
glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_ALPHA_ARB, GL_<SOURCE>);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA_ARB, GL_<OPERAND>);
Replace <SOURCE> and <OPERAND> with the desired values, such as GL_TEXTURE, GL_PRIMARY_COLOR, GL_SRC_COLOR, or GL_ONE_MINUS_SRC_COLOR.
4. Set the scale factor: You can also set a scale factor for the final result of the texture environment operation. This can be done using glTexEnvf with the GL_RGB_SCALE_ARB or GL_ALPHA_SCALE_ARB parameters:
glTexEnvf(GL_TEXTURE_ENV, GL_RGB_SCALE_ARB, <SCALE_FACTOR>);
glTexEnvf(GL_TEXTURE_ENV, GL_ALPHA_SCALE_ARB, <SCALE_FACTOR>);
With ARB_texture_env_combine, you can create more complex texture combinations than with the limited operations available in the standard fixed-function pipeline. However, the extension has been deprecated in favor of programmable shaders, which offer even more flexibility and power for creating advanced graphics effects.
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struct TextureEnvCombineState {
GLenum envMode;
GLenum combineRGB;
GLenum combineAlpha;
GLenum sourcesRGB[3];
GLenum sourcesAlpha[3];
GLenum operandsRGB[3];
GLenum operandsAlpha[3];
GLfloat rgbScale;
GLfloat alphaScale;
};
class ShaderGenerator {
public:
ShaderGenerator();
std::string generate(const TextureEnvCombineState& state);
// ...
private:
std::string getSourceString(GLenum source, bool isAlpha);
std::string getOperandString(GLenum operand, bool isAlpha);
// ...
};
generate() function to create a GLSL shader string based on the given TextureEnvCombineState. You'll need to translate ARB_texture_env_combine operations to their corresponding GLSL expressions.std::string ShaderGenerator::generate(const TextureEnvCombineState& state) {
std::stringstream shader;
shader << "#version 330 core\n";
shader << "uniform sampler2D tex;\n";
shader << "in vec2 texCoord;\n";
shader << "out vec4 FragColor;\n";
shader << "void main() {\n";
shader << " vec4 src0 = " << getSourceString(state.sourcesRGB[0], false) << ";\n";
shader << " vec4 src1 = " << getSourceString(state.sourcesRGB[1], false) << ";\n";
shader << " vec4 src2 = " << getSourceString(state.sourcesRGB[2], false) << ";\n";
shader << " src0.rgb = " << getOperandString(state.operandsRGB[0], false) << ";\n";
shader << " src1.rgb = " << getOperandString(state.operandsRGB[1], false) << ";\n";
shader << " src2.rgb = " << getOperandString(state.operandsRGB[2], false) << ";\n";
shader << " src0.a = " << getSourceString(state.sourcesAlpha[0], true) << ";\n";
shader << " src1.a = " << getSourceString(state.sourcesAlpha[1], true) << ";\n";
shader << " src2.a = " << getSourceString(state.sourcesAlpha[2], true) << ";\n";
shader << " src0.a = " << getOperandString(state.operandsAlpha[0], true) << ";\n";
shader << " src1.a = " << getOperandString(state.operandsAlpha[1], true) << ";\n";
shader << " src2.a = " << getOperandString(state.operandsAlpha[2], true) << ";\n";
// Implement the RGB and alpha operations based on the state.combineRGB and state.combineAlpha values.
shader << "}\n";
return shader.str();
}
getSourceString() and getOperandString() to convert GLenum values to GLSL expressions.std::string ShaderGenerator::getSourceString(GLenum source, bool isAlpha) {
switch (source) {
case GL_TEXTURE: return "texture(tex, texCoord)";
// Implement other
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getSourceString() and getOperandString().std::string ShaderGenerator::getSourceString(GLenum source, bool isAlpha) {
switch (source) {
case GL_TEXTURE: return "texture(tex, texCoord)";
case GL_CONSTANT: return "gl_TextureEnvColor";
case GL_PRIMARY_COLOR: return "gl_Color";
case GL_PREVIOUS: return isAlpha ? "gl_FragColor.a" : "gl_FragColor.rgb";
default: return "vec4(0.0)";
}
}
std::string ShaderGenerator::getOperandString(GLenum operand, bool isAlpha) {
std::string channel = isAlpha ? ".a" : ".rgb";
switch (operand) {
case GL_SRC_COLOR: return "src" + channel;
case GL_ONE_MINUS_SRC_COLOR: return "vec4(1.0) - src" + channel;
case GL_SRC_ALPHA: return isAlpha ? "src.a" : "vec3(src.a)";
case GL_ONE_MINUS_SRC_ALPHA: return isAlpha ? "1.0 - src.a" : "vec3(1.0 - src.a)";
default: return "vec4(0.0)";
}
}
With these helper functions, you can now complete the implementation of the generate() function by adding the RGB and alpha operations based on the state.combineRGB and state.combineAlpha values.
std::string ShaderGenerator::generate(const TextureEnvCombineState& state) {
// ... (previous code)
shader << " vec4 result;\n";
// Implement the RGB operation
switch (state.combineRGB) {
case GL_REPLACE:
shader << " result.rgb = src0.rgb;\n";
break;
case GL_MODULATE:
shader << " result.rgb = src0.rgb * src1.rgb;\n";
break;
case GL_ADD:
shader << " result.rgb = src0.rgb + src1.rgb;\n";
break;
case GL_ADD_SIGNED:
shader << " result.rgb = src0.rgb + src1.rgb - vec3(0.5);\n";
break;
case GL_INTERPOLATE:
shader << " result.rgb = mix(src0.rgb, src1.rgb, src2.rgb);\n";
break;
case GL_SUBTRACT:
shader << " result.rgb = src0.rgb - src1.rgb;\n";
break;
default:
shader << " result.rgb = vec3(0.0);\n";
}
// Implement the alpha operation
switch (state.combineAlpha) {
case GL_REPLACE:
shader << " result.a = src0.a;\n";
break;
case GL_MODULATE:
shader << " result.a = src0.a * src1.a;\n";
break;
case GL_ADD:
shader << " result.a = src0.a + src1.a;\n";
break;
case GL_ADD_SIGNED:
shader << " result.a = src0.a + src1.a - 0.5;\n";
break;
case GL_INTERPOLATE:
shader << " result.a = mix(src0.a, src1.a, src2.a);\n";
break;
case GL_SUBTRACT:
shader << " result.a = src0.a - src1.a;\n";
break;
default:
shader << " result.a = 0.0;\n";
}
// Apply the scale
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struct TextureEnvCombineState {
GLenum envMode;
GLenum combineRGB;
GLenum combineAlpha;
GLenum sourcesRGB[3];
GLenum sourcesAlpha[3];
GLenum operandsRGB[3];
GLenum operandsAlpha[3];
GLfloat rgbScale;
GLfloat alphaScale;
};
class SpirvShaderGenerator {
public:
SpirvShaderGenerator();
std::vector<uint32_t> generate(const TextureEnvCombineState& state);
// ...
private:
// Helper functions for generating SPIR-V code
};
generate() function to create a SPIR-V shader binary based on the given TextureEnvCombineState. This will involve several steps, including creating the shader header, declaring required capabilities and extensions, defining the necessary input and output variables, and translating the ARB_texture_env_combine state into SPIR-V instructions. Be aware that this process will be more involved than the GLSL example due to the binary nature of SPIR-V.Here's a very high-level outline of how the generate() function might look:
std::vector<uint32_t> SpirvShaderGenerator::generate(const TextureEnvCombineState& state) {
// 1. Initialize the SPIR-V module
// 2. Set up capabilities and extensions
// 3. Define input and output variables (e.g., gl_Position, gl_FragCoord, gl_FragColor)
// 4. Define uniforms (e.g., sampler2D)
// 5. Set up the main function
// 6. Translate the ARB_texture_env_combine state into SPIR-V instructions
// 7. Finalize the SPIR-V module
// Return the generated SPIR-V binary
}
Remember that this is just a high-level outline, and a complete implementation will require a thorough understanding of the SPIR-V specification and the chosen SPIR-V library. Due to the complexity of this task, I suggest starting with a simpler shader and gradually adding functionality to
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generate() function, I recommend using the SPIRV-Tools library. SPIRV-Tools is an extensive library developed by the Khronos Group that provides various functionalities to process SPIR-V modules. It has a C++ API for constructing, optimizing, and validating SPIR-V binary modules.GitHub repository: https://github.com/KhronosGroup/SPIRV-Tools
To use SPIRV-Tools, you can follow these steps:
#include <spirv-tools/libspirv.hpp>
Using SPIRV-Tools, you can build the SPIR-V shader binary module piece by piece, from setting up the header and defining capabilities to creating functions and emitting instructions. The library also provides a set of utilities for assembling and disassembling SPIR-V binary modules, which can be useful for debugging and testing your generator.
Note that SPIRV-Tools is focused on processing SPIR-V binary modules, so you will need a good understanding of the SPIR-V specification to use it effectively. Make sure you have read and understood the SPIR-V specification before diving into the implementation: https://www.khronos.org/registry/spir-v/specs/unified1/SPIRV.html
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generate() function for the SPIR-V shader generator is a complex task that is beyond the scope of a single response. However, I'll provide you with a high-level outline and some example code snippets to help you get started.To implement the generate() function, you will need to create a SPIR-V binary module piece by piece, using the SPIRV-Tools API. This process will involve setting up the header, defining capabilities, creating functions, and emitting instructions.
Here's a high-level outline of the generate() function:
Here's a basic example to get you started:
#include <spirv-tools/libspirv.hpp>
#include <vector>
#include <cstdint>
using namespace spvtools;
std::vector<uint32_t> generate(const TextureEnvCombineState& state) {
SpirvTools tools(SPV_ENV_UNIVERSAL_1_0);
spv::SpvBuildLogger logger;
spv_target_env target_env = SPV_ENV_UNIVERSAL_1_0;
// 1. Initialize the SPIR-V module and set up capabilities and extensions
spvtools::opt::IRContext ir_context(target_env, &logger);
ir_context.module()->SetHeader({0x07230203, 0, 0, 0}); // SPIR-V version 1.3
// Add necessary capabilities
ir_context.AddCapability(spv::Capability::CapabilityShader);
// 2. Define input and output variables
// ...
// 3. Define uniforms
// ...
// 4. Set up the main function
opt::BasicBlock main_block(0, &ir_context);
opt::Function main_function(0, spv::StorageClassFunction, 0, 0, 0, &ir_context);
// 5. Translate the ARB_texture_env_combine state into SPIR-V instructions
// ...
// Add return instruction and finalize the main function
main_block.AddInstruction(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpReturn));
main_function.AddBasicBlock(std::move(main_block));
// 6. Finalize the SPIR-V module and return the binary
ir_context.AddFunction(std::move(main_function));
std::vector<uint32_t> spirv_binary;
ir_context.module()->ToBinary(&spirv_binary, /* skip_nop = */ true);
return spirv_binary;
}
Please note that this example is just a starting point and does not cover the full implementation of the generate() function. To complete the implementation, you will need to add code for defining input and output variables, uniforms, and translating the ARB_texture_env_combine state into SPIR-V instructions, which will require a deep understanding of the SPIR-V specification and the SPIRV-Tools library API.
Additionally, you may want to optimize the generated SPIR-V code using the optimization passes provided by the SPIRV-Tools library.
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Step 2: Define input and output variables
// Define input variable for texture coordinates
uint32_t texCoordType = ir_context.GetFloatVectorType(2);
uint32_t texCoordId = ir_context.TakeNextId();
ir_context.AddVariable(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpVariable, texCoordType, texCoordId, spv::StorageClassInput));
// Define output variable for fragment color
uint32_t fragColorType = ir_context.GetFloatVectorType(4);
uint32_t fragColorId = ir_context.TakeNextId();
ir_context.AddVariable(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpVariable, fragColorType, fragColorId, spv::StorageClassOutput));
Step 3: Define uniforms
// Define sampler2D uniform for the texture
uint32_t sampler2DType = ir_context.GetSampler2DType();
uint32_t sampler2DId = ir_context.TakeNextId();
ir_context.AddVariable(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpVariable, sampler2DType, sampler2DId, spv::StorageClassUniformConstant));
Step 5: Translate the ARB_texture_env_combine state into SPIR-V instructions
// Sample the texture
uint32_t sampledTextureId = ir_context.TakeNextId();
main_block.AddInstruction(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpLoad, texCoordType, sampledTextureId, std::initializer_list<spv::Id>{texCoordId}));
uint32_t sampledColorId = ir_context.TakeNextId();
main_block.AddInstruction(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpImageSampleImplicitLod, fragColorType, sampledColorId, std::initializer_list<spv::Id>{sampler2DId, sampledTextureId}));
// Implement the ARB_texture_env_combine operation based on the state
// Note: This example only covers the GL_REPLACE operation for simplicity
if (state.combineRGB == GL_REPLACE) {
uint32_t resultId = ir_context.TakeNextId();
main_block.AddInstruction(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpLoad, fragColorType, resultId, std::initializer_list<spv::Id>{sampledColorId}));
main_block.AddInstruction(MakeUnique<opt::Instruction>(ir_context.TakeNextId(), spv::OpStore, 0, fragColorId, std::initializer_list<spv::Id>{resultId}));
}
// Implement other operations as needed
These snippets should be integrated into the generate() function example provided in a previous response. Keep in mind that the provided code is only a starting point and doesn't cover all possible combinations of the ARB_texture_env_combine state. You will need to extend the code to handle all required cases, taking into account the different sources, operands, and operations for both RGB and alpha channels, as well as the scaling factors.
Additionally, you should consider adding error checking and handling to ensure the generated SPIR-V code is correct and robust.