openGL学习笔记--三角形

转自：
https://learnopengl-cn.github.io/01%20Getting%20started/04%20Hello%20Triangle/

/*
画三角形
1、OpenGL仅当3D坐标在3个轴（x、y和z）上都为-1.0到1.0的范围内时才处理它
2、通常深度可以理解为z坐标，它代表一个像素在空间中和你的距离
3、顶点缓冲对象(VBO)会在GPU内存（通常被称为显存）中储存大量顶点
4、glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW)

    glBufferData是一个专门用来把用户定义的数据复制到当前绑定缓冲的函数。
    它的第一个参数是目标缓冲的类型：顶点缓冲对象当前绑定到GL_ARRAY_BUFFER目标上。
    第二个参数指定传输数据的大小(以字节为单位)；用一个简单的sizeof计算出顶点数据大小就行。
    第三个参数是我们希望发送的实际数据。

    第四个参数指定了我们希望显卡如何管理给定的数据。它有三种形式：

    GL_STATIC_DRAW ：数据不会或几乎不会改变。
    GL_DYNAMIC_DRAW：数据会被改变很多。
    GL_STREAM_DRAW ：数据每次绘制时都会改变。

    三角形的位置数据不会改变，每次渲染调用时都保持原样，
    所以它的使用类型最好是GL_STATIC_DRAW。
    如果，比如说一个缓冲中的数据将频繁被改变，
    那么使用的类型就是GL_DYNAMIC_DRAW或GL_STREAM_DRAW，
    这样就能确保显卡把数据放在能够高速写入的内存部分。


*/
#include<glad\glad.h>
#include<GLFW\glfw3.h>
#include <iostream>

using namespace std;
void framebuffer_size_callback(GLFWwindow *window, int width, int height);
void processInput(GLFWwindow *window);

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"
"}\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);

    GLFWwindow *window = glfwCreateWindow(800, 600, "Triangle", 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;
    }

    //编译顶点着色器
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);//着色器类型为GL_VERTEX_SHADER-->顶点着色器
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);//编译着色器

    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);//检测是否编译成功
    //如果编译失败，我们会用glGetShaderInfoLog获取错误消息，然后打印它

    if (!success){
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" <<infoLog<<endl;
    }

    //编译片段着色器
    unsigned int fragmentShader;
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);


    //着色器程序对象-->多个着色器合并之后并最终链接完成的版本
    unsigned int shaderProgram;
    shaderProgram = glCreateProgram();//函数创建一个程序，并返回新创建程序对象的ID引用


    //现在我们需要把之前编译的着色器附加到程序对象上，
    //然后用glLinkProgram链接它们：

    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success){
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << endl;
    }

    glUseProgram(shaderProgram);//激活程序对象

    //在把着色器对象链接到程序对象以后，记得删除着色器对象，我们不再需要它们了
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    float vertices[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f, 0.5f, 0.0f,
    };


    unsigned int VBO,VAO;//顶点缓冲对象

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);//生成一个VBO对象

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);//顶点缓冲对象的缓冲类型是GL_ARRAY_BUFFER

    //glBufferData是一个专门用来把用户定义的数据复制到当前绑定缓冲的函数
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, 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);

    // 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);

        // 渲染一个物体时要使用着色器程序
        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, 3);
        // 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);

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


    return 0;
}
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);
}
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}