c++ - Opengl - 渲染不同的顶点格式

Question

我正在寻找一种很好的方法来渲染具有不同顶点布局的网格对象，而不需要很大的努力(例如，为每个顶点布局定义一个渲染器类)。您可以在下面看到一些不同顶点格式的示例。

enum EVertexFormat
{
    VERTEX_FORMAT_UNDEFINED = -1,
    VERTEX_FORMAT_P1 = 0,
    VERTEX_FORMAT_P1N1,
    VERTEX_FORMAT_P1N1UV,
    VERTEX_FORMAT_P1N1C1,
    VERTEX_FORMAT_P1N1UVC1,
};

// the simplest possible vertex -- position only 
struct SVertexP1
{
    math::Vector3D m_position;      // position of the vertex
};

struct SVertexP1N1
{
    math::Vector3D m_position;      // position of the vertex
    math::Vector3D m_normal;        // normal of the vertex
};

// a typical vertex format with position, vertex normal
// and one set of texture coordinates
struct SVertexP1N1UV
{
    math::Vector3D m_position;      // position of the vertex
    math::Vector3D m_normal;        // normal of the vertex
    math::Vector2D m_uv;            // (u,v) texture coordinate
};

struct SVertexP1N1C1
{
    math::Vector3D m_position;      // position of the vertex
    math::Vector3D m_normal;        // normal of the vertex
    uint32_t m_color_u32;           // color of the vertex
};

struct SVertexP1N1UVC1
{
    math::Vector3D m_position;      // position of the vertex
    math::Vector3D m_normal;        // normal of the vertex
    math::Vector2D m_uv;            // (u,v) texture coordinate
    uint32_t m_color_u32;           // color of the vertex
};

背景是，我想渲染不同的对象。其中一些是不拥有纹理坐标或法线的基元(例如平面、球体)。另一方面，我想渲染具有法线、纹理坐标等的更复杂的对象。是否有一种聪明的方法或设计来避免对多个渲染器类进行编程，而是使用单个渲染器类？我知道，这也会影响着色器。

Answer 1

您可以为每个顶点结构提供一个静态方法，可能称为 EnableVertexAttribArray 或类似名称。在此静态方法中，您在 GL_ARRAY_BUFFER 中设置顶点布局，假设已绑定(bind)正确的数组缓冲区。

struct SVertexP1N1
{
    math::Vector3D m_position;      // position of the vertex
    math::Vector3D m_normal;        // normal of the vertex
    static void EnableVertexAttribArray()
    {
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(SVertexP1N1), (const GLvoid*)offsetof(SVertexP1N1, m_position));
        glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(SVertexP1N1), (const GLvoid*)offsetof(SVertexP1N1, m_normal));
        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(1);
    }
};

然后你可以根据顶点结构创建一个顶点缓冲区的模板类。例如，

template <class VertexType> class vertex_buffer
{
public:
    typedef VertexType vertex_type;

    vertex_buffer()
    {
        glGenVertexArrays(1, &m_vao);
        glGenBuffers(1, &m_vbo);
        glGenBuffers(1, &m_ibo);
        glBindVertexArray(m_vao);
        glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_ibo);
        vertex_type::EnableVertexAttribArray(); // <--------
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindVertexArray(0);
    }

    ~vertex_buffer()
    {
        glDeleteVertexArrays(1, &m_vao);
        glDeleteBuffers(1, &m_vbo);
        glDeleteBuffers(1, &m_ibo);
    }

    // ...

    void draw()
    {
        glBindVertexArray(m_vao);
        glBindBuffer(GL_ARRAY_BUFFER, m_vbo);
        glDrawElements(GL_TRIANGLES, m_indices.size(), GL_UNSIGNED_INT, NULL);
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindVertexArray(0);
    }

private:
    GLuint m_vao;
    GLuint m_vbo;
    GLuint m_ibo;
    std::vector<vertex_type> m_vertices;
    std::vector<GLuint> m_indices;
}