shader_generator - ryzom/ryzomcore GitHub Wiki

Person:

• Explain how the legacy ARB_texture_env_combine works

ChatGPT:

• ARB_texture_env_combine is a legacy OpenGL extension that provides a more flexible way of combining textures during the texturing process. It was introduced in OpenGL 1.3 and later deprecated in OpenGL 3.0, though it can still be found in older codebases and legacy systems. This extension extended the functionality of the fixed-function pipeline, which was the main way of handling graphics rendering before programmable shaders became popular.

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:

1. Set the environment mode: First, you need to set the environment mode for each texture unit to GL_COMBINE_ARB using glTexEnvf:

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE_ARB);

2. Specify the combine operation: Next, you need to set the specific operation you want to perform on the texture unit. This can be done using glTexEnvf with the GL_COMBINE_RGB_ARB or GL_COMBINE_ALPHA_ARB parameters:

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.

Person:

• Implement a GLSL shader generator in C++ that implements all the features of ARB_texture_env_combine.

ChatGPT:

• Creating a full-fledged GLSL shader generator in C++ that implements all the features of ARB_texture_env_combine is quite a complex task, and it's beyond the scope of a single response. However, I'll provide you with a high-level outline of how you can approach this problem, which you can use as a starting point for your implementation.

1. Define data structures and classes to represent the ARB_texture_env_combine state.

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);
    // ...
};

1. Implement the 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();
}

1. Implement the helper functions 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

Person:

• Keep going

ChatGPT:

• As requested, I will continue providing you with more details for implementing the helper functions 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

Person:

• Implement a SPIR-V shader generator in C++ that implements all the features of ARB_texture_env_combine.

ChatGPT:

• Creating a SPIR-V shader generator that implements all the features of ARB_texture_env_combine is a complex task, especially since SPIR-V is a low-level binary representation of a shader. However, I can guide you through the high-level approach, which you can use as a starting point for your implementation. Note that this guide assumes familiarity with SPIR-V and the SPIR-V specification.

1. If you haven't already, familiarize yourself with the SPIR-V specification: https://www.khronos.org/registry/spir-v/specs/unified1/SPIRV.html
2. Use an existing SPIR-V library, such as SPIRV-Cross or SPIRV-Tools, to help generate and manipulate SPIR-V code. SPIRV-Cross (https://github.com/KhronosGroup/SPIRV-Cross ) is a library that can be used to convert SPIR-V to other shader languages or to manipulate SPIR-V shaders. SPIRV-Tools (https://github.com/KhronosGroup/SPIRV-Tools ) is a more extensive library that provides various functionalities to process SPIR-V modules.
3. Define a data structure to represent the ARB_texture_env_combine state, similar to the previous GLSL example:

struct TextureEnvCombineState {
    GLenum envMode;
    GLenum combineRGB;
    GLenum combineAlpha;
    GLenum sourcesRGB[3];
    GLenum sourcesAlpha[3];
    GLenum operandsRGB[3];
    GLenum operandsAlpha[3];
    GLfloat rgbScale;
    GLfloat alphaScale;
};

1. Create a class for the SPIR-V shader generator:

class SpirvShaderGenerator {
public:
    SpirvShaderGenerator();
    std::vector<uint32_t> generate(const TextureEnvCombineState& state);
    // ...
private:
    // Helper functions for generating SPIR-V code
};

1. Implement the 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.
2. Use the helper functions provided by the chosen SPIR-V library to generate the required instructions for the shader. This may include creating functions, declaring variables, generating arithmetic instructions, and more. Keep in mind that generating SPIR-V is generally more low-level than generating GLSL, so you will need to manage details like IDs, types, and decorations manually.

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

Person:

• Suggest a good SPIR-V library to implement the generate function

ChatGPT:

• For implementing the 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:

1. Clone the repository and follow the build instructions provided in the README: https://github.com/KhronosGroup/SPIRV-Tools#build
2. Include the appropriate headers in your project, for example:

#include <spirv-tools/libspirv.hpp>

1. Familiarize yourself with the SPIRV-Tools API and examples: https://github.com/KhronosGroup/SPIRV-Tools#example

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

Person:

• Implement the generate function

ChatGPT:

• Implementing the full 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:

1. Initialize the SPIR-V module and set up capabilities and extensions
2. Define input and output variables (e.g., gl_Position, gl_FragCoord, gl_FragColor)
3. Define uniforms (e.g., sampler2D)
4. Set up the main function
5. Translate the ARB_texture_env_combine state into SPIR-V instructions
6. Finalize the SPIR-V module and return the binary

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.

Person:

• Provide example source code for steps 2, 3 and 5.

ChatGPT:

• Below are example code snippets for steps 2, 3, and 5. Note that these snippets are meant to guide you, and they don't cover all possible scenarios for the ARB_texture_env_combine state. You will need to adapt the code to handle all combinations of state parameters.

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.