struct QuadVertex
{
    glm::vec3 Position;
    glm::vec4 Color;
    glm::vec2 TexCoord;
    float TexIndex; // 关键！用于在着色器中选择纹理
};

// BatchRenderer2D.cpp
const size_t MaxQuadCount = 10000;
const size_t MaxVertexCount = MaxQuadCount * 4;
const size_t MaxIndexCount = MaxQuadCount * 6;

BatchRenderer2D::BatchRenderer2D()
{
    m_QuadVertexBuffer = new QuadVertex[MaxVertexCount]; // 在CPU端分配一个大数组

    m_QuadVAO = new VertexArray();
    m_QuadVBO = new VertexBuffer(MaxVertexCount * sizeof(QuadVertex), GL_DYNAMIC_DRAW); // 创建空的动态VBO

    // 设置顶点布局
    VertexBufferLayout layout;
    layout.Push<float>(3); // Position
    layout.Push<float>(4); // Color
    layout.Push<float>(2); // TexCoord
    layout.Push<float>(1); // TexIndex
    m_QuadVAO->AddBuffer(*m_QuadVBO, layout);

    // 生成索引缓冲 (这部分数据是固定的，可以一次性生成)
    uint32_t indices[MaxIndexCount];
    uint32_t offset = 0;
    for (size_t i = 0; i < MaxIndexCount; i += 6)
    {
        indices[i + 0] = offset + 0;
        indices[i + 1] = offset + 1;
        indices[i + 2] = offset + 2;
        indices[i + 3] = offset + 2;
        indices[i + 4] = offset + 3;
        indices[i + 5] = offset + 0;
        offset += 4;
    }
    m_QuadIBO = new IndexBuffer(indices, MaxIndexCount);
    // ...
}

// BatchRenderer2D.cpp
void BatchRenderer2D::BeginScene()
{
    m_QuadVertexBufferPtr = m_QuadVertexBuffer; // 重置指向CPU缓冲区的指针
    m_IndexCount = 0; // 重置索引计数
    m_TextureSlotIndex = 1; // 0号槽留给白色纹理
}

void BatchRenderer2D::EndScene()
{
    // 计算这一帧填充了多少数据
    GLsizeiptr size = (uint8_t*)m_QuadVertexBufferPtr - (uint8_t*)m_QuadVertexBuffer;
    
    // 将CPU缓冲区的数据上传到GPU的动态VBO中
    m_QuadVBO->Bind();
    glBufferSubData(GL_ARRAY_BUFFER, 0, size, m_QuadVertexBuffer);

    Flush(); // Flush 函数执行绘制
}

void BatchRenderer2D::Flush()
{
    // 绑定所有使用的纹理
    for (uint32_t i = 0; i < m_TextureSlotIndex; i++)
        m_TextureSlots[i]->Bind(i);

    // 绑定VAO和着色器
    m_Shader->Bind();
    m_QuadVAO->Bind();
    
    // 执行一次绘制调用
    glDrawElements(GL_TRIANGLES, m_IndexCount, GL_UNSIGNED_INT, nullptr);
}

// BatchRenderer2D.cpp
void BatchRenderer2D::DrawQuad(const glm::vec2& position, const glm::vec2& size, const glm::vec4& color)
{
    // 如果缓冲区满了，就先提交一次
    if (m_IndexCount >= MaxIndexCount)
    {
        EndScene();
        BeginScene();
    }

    float textureIndex = 0.0f; // 0.0f 代表纯色（使用白色纹理）

    // 计算四边形的四个顶点，并填充到 CPU 缓冲区中
    m_QuadVertexBufferPtr->Position = { position.x, position.y, 0.0f };
    m_QuadVertexBufferPtr->Color = color;
    m_QuadVertexBufferPtr->TexCoord = { 0.0f, 0.0f };
    m_QuadVertexBufferPtr->TexIndex = textureIndex;
    m_QuadVertexBufferPtr++;
    // ... 填充另外3个顶点 ...

    m_IndexCount += 6;
}

// 带纹理的版本
void BatchRenderer2D::DrawQuad(const glm::vec2& position, const glm::vec2& size, const std::shared_ptr<Texture>& texture)
{
    // ... 检查缓冲区是否已满 ...

    // 查找这个纹理是否已经在本批次中被绑定
    float textureIndex = 0.0f;
    for (uint32_t i = 1; i < m_TextureSlotIndex; i++)
    {
        if (*m_TextureSlots[i].get() == *texture.get())
        {
            textureIndex = (float)i;
            break;
        }
    }

    // 如果没找到，就把它添加到下一个可用的纹理槽
    if (textureIndex == 0.0f)
    {
        textureIndex = (float)m_TextureSlotIndex;
        m_TextureSlots[m_TextureSlotIndex] = texture;
        m_TextureSlotIndex++;
    }

    // ... 填充四个顶点的数据，这次 TexIndex 是算出来的 ...
}