0.详细教程可看https://learnopengl-cn.github.io/01%20Getting%20started/04%20Hello%20Triangle/
1.可以简单地认为VAO的作用是这样的：
由于每渲染一次物体就要用一个VBO，而每次绑定一次VBO就要设置各个的顶点的属性，启动各个属性，代码十分复杂，复用性很差，因为每个物体的属性个数什么的都不一样（也就是说不是同构的），循环根本解决不了。所以就抽象出一层VAO来解决这个问题，相当于复用代码，使之简介快速。只在一开始将所有的VBO绑定对应的VAO就OK了，之后渲染的时候完全就可以绑定VAO，然后你就循环处理同构的VAO就好了。
2.其实EBO的作用也可以简单地理解为复用跟减少冗余，貌似还可以节约内存跟缓存：
否则的话VBO中储存大量的数据
3.VAO中存储着VBO的信息和EBO的信息
所以正确的绑定顺序是VAO、VBO、EBO,将后两者的信息也绑定进VAO中去啊
如果不适用VAO的话，那么最后一部分每次渲染都要设置第四部分的顶点属性，要好多行好多行，而用了VAO就一行绑定VAO就OK了啊，嘻嘻
4.创建相同的两个三角形，但对它们的数据使用不同的VAO和VBO：
#include <glad/glad.h>
#include <GLFW/glfw3.h> #include <iostream> void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window); // settings
const unsigned int SCR_WIDTH = ;
const unsigned int SCR_HEIGHT = ; const char *vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
const char *fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\n\0"; int main()
{
// glfw: initialize and configure
// ------------------------------
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, );
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, );
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); #ifdef __APPLE__
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X
#endif // glfw window creation
// --------------------
GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
if (window == NULL)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -;
}
glfwMakeContextCurrent(window);
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); // glad: load all OpenGL function pointers
// ---------------------------------------
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -;
} // build and compile our shader program
// ------------------------------------
// vertex shader
int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, , &vertexShaderSource, NULL);
glCompileShader(vertexShader);
// check for shader compile errors
int success;
char infoLog[];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, , NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// fragment shader
int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, , &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// check for shader compile errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, , NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// link shaders
int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shaderProgram, , NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader); // set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
float firstTriangle[] = {
-0.9f, -0.5f, 0.0f, // left
-0.0f, -0.5f, 0.0f, // right
-0.45f, 0.5f, 0.0f, // top
};
float secondTriangle[] = {
0.0f, -0.5f, 0.0f, // left
0.9f, -0.5f, 0.0f, // right
0.45f, 0.5f, 0.0f // top
};
unsigned int VBOs[], VAOs[];
glGenVertexArrays(, VAOs); // we can also generate multiple VAOs or buffers at the same time
glGenBuffers(, VBOs);
// first triangle setup
// --------------------
glBindVertexArray(VAOs[]);
glBindBuffer(GL_ARRAY_BUFFER, VBOs[]);
glBufferData(GL_ARRAY_BUFFER, sizeof(firstTriangle), firstTriangle, GL_STATIC_DRAW);
glVertexAttribPointer(, , GL_FLOAT, GL_FALSE, * sizeof(float), (void*)); // Vertex attributes stay the same
glEnableVertexAttribArray();
// glBindVertexArray(0); // no need to unbind at all as we directly bind a different VAO the next few lines
// second triangle setup
// ---------------------
glBindVertexArray(VAOs[]); // note that we bind to a different VAO now
glBindBuffer(GL_ARRAY_BUFFER, VBOs[]); // and a different VBO
glBufferData(GL_ARRAY_BUFFER, sizeof(secondTriangle), secondTriangle, GL_STATIC_DRAW);
glVertexAttribPointer(, , GL_FLOAT, GL_FALSE, , (void*)); // because the vertex data is tightly packed we can also specify 0 as the vertex attribute's stride to let OpenGL figure it out
glEnableVertexAttribArray();
// glBindVertexArray(0); // not really necessary as well, but beware of calls that could affect VAOs while this one is bound (like binding element buffer objects, or enabling/disabling vertex attributes) // uncomment this call to draw in wireframe polygons.
//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); // render loop
// -----------
while (!glfwWindowShouldClose(window))
{
// input
// -----
processInput(window); // render
// ------
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT); glUseProgram(shaderProgram);
// draw first triangle using the data from the first VAO
glBindVertexArray(VAOs[]);
glDrawArrays(GL_TRIANGLES, , );
// then we draw the second triangle using the data from the second VAO
glBindVertexArray(VAOs[]);
glDrawArrays(GL_TRIANGLES, , ); // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);
glfwPollEvents();
} // optional: de-allocate all resources once they've outlived their purpose:
// ------------------------------------------------------------------------
glDeleteVertexArrays(, VAOs);
glDeleteBuffers(, VBOs); // glfw: terminate, clearing all previously allocated GLFW resources.
// ------------------------------------------------------------------
glfwTerminate();
return ;
} // process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
glfwSetWindowShouldClose(window, true);
} // glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
// make sure the viewport matches the new window dimensions; note that width and
// height will be significantly larger than specified on retina displays.
glViewport(, , width, height);
}