LearnOpenGL学习笔记1-Hello Triangle_learnopengl源码-优快云博客

本文链接：https://blog.youkuaiyun.com/LLLawrenceQ/article/details/143224595

LearnOpenGL学习笔记1-Hello Triangle

原网站链接： https://learnopengl.com/Getting-started/Hello-Triangle
源码链接：https://github.com/JoeyDeVries/LearnOpenGL

这一节主要内容就是VBO、VAO、EBO三个对象的使用，跟平时编程习惯不太一样，OpenGL使用对象都是先绑定然后进行操作或者使用。这是OpenGL最基础的内容，一定要吃透。

VBO

VBO: vertex buffer object 顶点缓存对象，用来管理内存，可以在GPU中储存大量的顶点数据。优势是可以一次性发送大量数据给显卡，并在显卡中缓存。为了提升效率尽量把数据一次性发送给显卡。

unsigned int VBO;
glGenBuffers(1, &VBO);		//生成数量为1的缓存对象
glBindBuffer(GL_ARRAY_BUFFER, VBO);	// 将VBO绑定到GL_ARRAY_BUFFER类型上，对于每种缓存类型，只能绑定一个缓存对象,绑定之后对于GL_ARRAY_BUFFER的所有操作都会修改VBO对象指向的缓存
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); // 使用这个命令将vertices中的数据拷贝到VBO中
// 完成这些操作之后我们已经将顶点数据储存到了显卡中，并用VBO进行管理

glBufferData的最后一个参数含义是指定显卡处理给定数据的方式，有三种方式

GL_STREAM_DRAW：数据不变，GPU调用不频繁
GL_STATIC_DRAW：数据不变，GPU调用频繁
GL_DYNAMIC_DRAW：数据经常改变，并且调用频繁

VAO

VAO: vertex array object 顶点数组对象，用于解析顶点数据，创建方式与VBO类似，绑定后直到下一次绑定之前的顶点属性都会保存在VAO中。

unsigned int VAO;						
glGenVertexArrays(1, &VAO);		// 生成数量为1的数组对象
glBindVertexArrays(VAO);		// 绑定数组对象，绑定之后，所有相关修改会作用于VAO
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);		// 告诉OpenGL如何解析顶点数据，配置（location=0）的顶点属性
glEnableVertexAttribArray(0);  // 顶点属性开启可用，默认是不可用的
[...]
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);	// 使用VAO对象绘制三角形

glVertexAttribPointer函数原型：glVertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const void *pointer);

index：表示vertex属性的编号，在shader中对应的是location
size：表示一组顶点属性的个数，注意不是总数，如果是vec3的属性那就填3
type：数据类型比如GL_FLOAT
normalized：是否要把数据正规化，不是归一化的意思，而是把整型数据统一转换为（1,0,-1）
stride：跨距
pointer：目标位置距离起始位置的偏移

经过测试：一个VBO可以有多个VAO属性，一个VAO也可以绑定多个VBO，甚至可以用多个VAO同时绑定同一块VBO数据。
请添加图片描述

EBO

EBO：element buffer objects 元素缓存对象，用来指导OpenGL如何绘制面元。存储的是面片使用的顶点序号，使用时根据索引找到对应顶点进行渲染。

float vertices[] = {
     0.5f,  0.5f, 0.0f,  // top right
     0.5f, -0.5f, 0.0f,  // bottom right
    -0.5f, -0.5f, 0.0f,  // bottom left
    -0.5f,  0.5f, 0.0f   // top left 
};
unsigned int indices[] = {  // note that we start from 0!
    0, 1, 3,   // first triangle
    1, 2, 3    // second triangle
};  

unsigned int EBO;
glGenBuffers(1, &EBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW); // EBO使用方法与VBO类似，区别在于EBO绑定的缓存类型是GL_ELEMENT_ARRAY_BUFFER
[...]
//绘制三角形
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);	// 改用glDrawElements绘制三角形

完整源码：

#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 = 800;
const unsigned int SCR_HEIGHT = 600;

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, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#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 -1;
    }
    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 -1;
    }


    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // fragment shader
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // link shaders
    unsigned 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, 512, 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 vertices[] = {
         0.5f,  0.5f, 0.0f,  // top right
         0.5f, -0.5f, 0.0f,  // bottom right
        -0.5f, -0.5f, 0.0f,  // bottom left
        -0.5f,  0.5f, 0.0f   // top left 
    };
    unsigned int indices[] = {  // note that we start from 0!
        0, 1, 3,  // first Triangle
        1, 2, 3   // second Triangle
    };
    unsigned int VBO, VAO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
    glBindBuffer(GL_ARRAY_BUFFER, 0); 

    // remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
    //glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
    glBindVertexArray(0); 


    // 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);

        // draw our first triangle
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
        //glDrawArrays(GL_TRIANGLES, 0, 6);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        // glBindVertexArray(0); // no need to unbind it every time 
 
        // 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(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);
    glDeleteProgram(shaderProgram);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// 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(0, 0, width, height);
}