Dawn/src/dawnopengl/display/shader/ShaderStructure.hpp

// Copyright (c) 2023 Dominic Masters
// 
// This software is released under the MIT License.
// https://opensource.org/licenses/MIT

#pragma ocne
#include "display/shader/ShaderParameter.hpp"

namespace Dawn {
  enum class ShaderOpenGLStructureType {
    STD140
  };

  struct IShaderStructure {
    std::string structureName;
    size_t offset;
    enum ShaderOpenGLStructureType structureType;
    size_t size;
    // size_t count;
    std::vector<struct ShaderParameter> parameters;
    GLint location = -1;
    GLuint buffer = -1;
  };
  
  template<typename T>
  struct ShaderStructure final : public IShaderStructure {
    public:
      /**
       * Constructs a new shader structure. Shader structures allow for larger
       * amounts/volumes of data to be passed to the shader in a single call.
       * Ideally I wouldn't really need this as I wanted the entire shader to
       * basically be a single large structure, but OpenGL doesn't support that
       * so I have to do this instead.
       * 
       * @param structureName Structure name within the shader.
       * @param offset Offset, within the data structure, that this structure
       *               starts at.
       * @param structureType The type of structure data format to use.
       * @param getParameters A callback that, when invoked, will populate the
       *                      parameters vector with the parameters for this
       *                      structure.
       */
      ShaderStructure(
        const std::string &structureName,
        const void *offset,
        const enum ShaderOpenGLStructureType structureType,
        std::function<
          void(const T&, std::vector<struct ShaderParameter>&)
        > getParameters
      ) {
        this->structureName = structureName;
        this->offset = (size_t)offset;
        this->structureType = structureType;
        this->size = sizeof(T);
        this->parameters = std::vector<struct ShaderParameter>();

        T dummy;
        getParameters(dummy, this->parameters);

        // Update offsets.
        std::for_each(
          this->parameters.begin(),
          this->parameters.end(),
          [&](struct ShaderParameter &param) {
            param.offset -= (size_t)(&dummy);

            // Check for non-aligned OpenGL structures.
            if(param.offset % sizeof(glm::vec4) != 0) {
              assertUnreachable(
                "%s%s%s",
                "Non-aligned OpenGL structure detected on param ",
                param.name.c_str(),
                "!\nEnsure you have padded correctly."
              );
            }
          }
        );

      }
  };
}