mesh_data_gpu.hpp

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// This file is part of the Rendering Engine project.
// Author: Alexander Obzherin <alexanderobzherin@gmail.com>
// Copyright (c) 2025 Alexander Obzherin
// Distributed under the terms of the zlib License. See LICENSE.md for details.
 
#pragma once
 
#include <string>
#include <memory>
#include <vector>
#include "vertex_declarations.hpp"
 
namespace rendering_engine
{
class IRenderer;
class IMeshRenderResources;
class Model;
 
/**
 * @brief Types of supported mesh layouts for GPU upload and rendering.
 */
enum class MeshType
{
    None,      ///< Undefined or not yet set.
    Sprite2D,  ///< 2D sprite mesh (typically for UI or simple quads).
    Billboard, ///< 3D billboard mesh (sprites that face the camera).
    Surface    ///< Full 3D surface mesh (models with normals/tangents, etc.).
};
 
/**
 * @brief Manages mesh data in RAM and GPU, including upload and release operations.
 *
 * Supports on-demand composition of different vertex buffer formats and maintains
 * all intermediate mesh data required for rendering or further processing (e.g., collision).
 */
class MeshDataGpu
{
public:
    /**
     * @brief Constructs an empty MeshDataGpu object.
     *
     * This constructor is typically used when the mesh data will be filled
     * or generated procedurally before being uploaded to the GPU.
     *
     * @param renderer Pointer to the rendering backend interface.
     */
    MeshDataGpu(IRenderer* renderer);
    /**
     * @brief Construct a MeshDataGpu instance.
     * @param filename Path to the model file
     * @param renderer Pointer to the rendering backend interface.
     */
    MeshDataGpu(const std::string& filename, IRenderer* renderer);
 
    /**
     * @brief Constructs a MeshDataGpu instance from in-memory model data.
     *
     * This version loads a model directly from a raw file buffer in memory. 
     * It allows meshes to be created from packed assets, archives, network 
     * transfers, or any other non-filesystem source. After loading the model, 
     * vertex and index data are uploaded to GPU buffers the same way as in 
     * the file-based constructor.
     *
     * @param fileBytes Raw contents of the model file.
     * @param renderer Pointer to the rendering backend interface.
     */
    MeshDataGpu(std::vector<uint8_t> const& fileBytes, IRenderer* renderer);
 
    /**
     * @brief Destructor. Releases GPU resources if allocated.
     */
    ~MeshDataGpu();
 
    /**
     * @brief Upload mesh data to the GPU using the current mesh type.
     */
    void UploadToGPU();
 
    /**
     * @brief Release GPU resources associated with this mesh.
     */
    void ReleaseFromGPU();
 
    /**
     * @brief Check if mesh data is currently uploaded to GPU.
     * @return True if GPU resources are resident, false otherwise.
     */
    bool IsOnGPU() const;
 
    /**
     * @brief Creates a 1�1 unit quad centered at the origin.
     *
     * The quad spans from -0.5 to +0.5 on both X and Y axes and uses
     * counterclockwise winding. Suitable as a base mesh for sprites
     * or 2D UI elements.
     */
    void CreateQuad2D();
 
    /**
     * @brief Get the size (in bytes) of the vertex buffer on GPU.
     * @return Size in bytes of the GPU vertex buffer.
     */
    size_t GetGpuVertexBufferSize() const;
 
    /**
     * @brief Get the size (in bytes) of the index buffer on GPU.
     * @return Size in bytes of the GPU index buffer.
     */
    size_t GetGpuIndexBufferSize()  const;
 
    /**
     * @brief Get the size (in bytes) of the vertex buffer in RAM.
     * @return Size in bytes of the CPU-side vertex data.
     */
    size_t GetCpuVertexBufferSize() const;
 
    /**
     * @brief Get the size (in bytes) of the index buffer in RAM.
     * @return Size in bytes of the CPU-side index data.
     */
    size_t GetCpuIndexBufferSize()  const;
 
    /**
     * @brief Get the interface for mesh GPU resources (Vulkan or other backend).
     * @return Pointer to the backend-specific IMeshRenderResources implementation.
     */
    IMeshRenderResources* GetMeshRenderResources();
 
    /**
     * @brief Returns a constant reference to the 2D vertex positions.
     */
    const std::vector<glm::vec2>& GetPositions2D() const { return mPositions2D; }
 
    /**
     * @brief Returns a constant reference to the 3D vertex positions.
     */
    const std::vector<glm::vec3>& GetPositions() const { return mPositions; }
 
    /**
     * @brief Returns a constant reference to the vertex colors.
     */
    const std::vector<glm::vec4>& GetColors() const { return mColor; }
 
    /**
     * @brief Returns a constant reference to the vertex normals.
     */
    const std::vector<glm::vec3>& GetNormals() const { return mNormals; }
 
    /**
     * @brief Returns a constant reference to the texture coordinates.
     */
    const std::vector<glm::vec2>& GetTexCoords() const { return mTexCoords; }
 
    /**
     * @brief Returns a constant reference to the vertex tangents.
     */
    const std::vector<glm::vec3>& GetTangents() const { return mTangents; }
 
    /**
     * @brief Returns a constant reference to the mesh indices.
     */
    const std::vector<uint32_t>& GetIndices() const { return mIndices; }
 
protected:
    /**
     * @brief Load a model from file and extract mesh data to RAM.
     * @param path Path to the model file (e.g., FBX).
     */
    void LoadModel(std::string path);
 
    void LoadModel(std::vector<uint8_t> const& fileBytes);
    /**
     * @brief Calculate and cache sizes of RAM buffers for statistics or debugging.
     */
    void CalculateMeshParameters();
 
    /**
     * @brief Compose a vertex buffer for 2D meshes (e.g., sprites).
     * @return Vector of Vertex2D structures.
     */
    std::vector<Vertex2D> ComposeVertex2DBuffer();
 
    /**
     * @brief Compose a vertex buffer for unlit 3D meshes (e.g., billboards, particles).
     * @return Vector of VertexPositionTextureColor structures.
     */
    std::vector<VertexPositionColorTexture> ComposeUnlitBuffer();
 
    /**
     * @brief Compose a vertex buffer for lit 3D meshes (with normals, tangents).
     * @return Vector of VertexPositionTextureColorNormalTangent structures.
     */
    std::vector<VertexPositionColorTextureNormalTangent> ComposeLitBuffer();
 
private:
    std::string mPath;
    IRenderer* mRenderer;
 
    MeshType mMeshType;
 
    std::vector<glm::vec2> mPositions2D;
    std::vector<glm::vec3> mPositions;
    std::vector<glm::vec4> mColor;
    std::vector<glm::vec3> mNormals;        
    std::vector<glm::vec2> mTexCoords;
    std::vector<glm::vec3> mTangents;       
    std::vector<uint32_t> mIndices;
 
    size_t mSizeOfVerticesBytes;
    size_t mSizeOfIndicesBytes;
 
    std::unique_ptr<IMeshRenderResources> mGpuHandle;
};
 
} // namespace rendering_engine