VAO和元素缓冲区对象

问题描述

我一直在阅读有关VAO如何与VBO一起工作的信息.据我了解，当我们调用glVertexAttribPointer时，VAO仅存储有关VBO的状态信息.我的问题是，什么时候它会存储有关EBO的状态(用于索引图形)，当调用glVertexAttribPointer时，它是否同时保存两种状态?

I've been reading a bit about how VAOs work with VBOs. As far as I understand, the VAO only stores state information about a VBO when we call glVertexAttribPointer. My question is, when does it store state about an EBO (for indexed drawing), does it save state for both when glVertexAttribPointer is called?

//Vertices of the rectangle
std::vector<GLfloat> vertices
{
    0.5f,  0.5f, 0.0f,  // Top Right
    0.5f, -0.5f, 0.0f,  // Bottom Right
    -0.5f,  0.5f, 0.0f,  // Top Left 
    -0.5f, -0.5f, 0.0f,  // Bottom Left
};

//Indices of the triangle
std::vector<GLuint> indices
{
    0, 1, 3,
    0, 3, 2
};


GLuint VAO, VBO, EBO; 
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);

glBindVertexArray(VAO); //Bind the VAO

//Bind the buffers
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);

glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(GLfloat), &vertices[0], GL_STATIC_DRAW);

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);

glBindVertexArray(0); //Unbind the VAO

//Supply Index Buffer information
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(GLuint), &indices[0], GL_STATIC_DRAW);

glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

//Custom shader class that stores the program to be used at render time
Shader shader("..path_to_shader\\shaders\\vertexshader.vert", "..path_to_shader\\shaders\\fragmentshader.frag");

while (!glfwWindowShouldClose(window))
{
    glUseProgram(shader.Program());
    glBindVertexArray(VAO); //Bind the VAO to draw.
    glClearBufferfv(GL_COLOR, 0, &color[0]);

    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

    glfwPollEvents();
    glfwSwapBuffers(window);

    glBindVertexArray(0);
    glUseProgram(0);
}

推荐答案

来自 opengl.org :

在下面，位于索引缓冲区

对于GL_ARRAY_BUFFER，当您调用glVertexAttribPointer时，VAO将保存绑定.基本上是因为GL_ARRAY_BUFFER绑定不是VAO状态的一部分.因此，调用glBindBuffer(GL_ARRAY_BUFFER, vertexBufferHandle)不会对VAO的状态产生任何作用.

For GL_ARRAY_BUFFER the VAO will save the binding when you call glVertexAttribPointer. It is basically because the GL_ARRAY_BUFFER binding is not part of the VAO's state. So calling glBindBuffer(GL_ARRAY_BUFFER, vertexBufferHandle) won't do anything with the VAO's state.

对于GL_ELEMENT_ARRAY_BUFFER并非如此:VAO(如果已绑定)将在您调用glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferHandle)时将索引缓冲区绑定保存到其状态.

For GL_ELEMENT_ARRAY_BUFFER it's not the case:the VAO (if bound) will save your index buffer binding to it's state when you call glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferHandle).

关于OpenGL 索引缓冲和 opengl-tutorial.org 上的另一基本内容.

There are great tutorials about OpenGL indexed buffering and another basic stuff on opengl-tutorial.org.

这篇关于VAO和元素缓冲区对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！