openGL学习<四>、着色器

//
// Created by sry on 2021/7/6.
//
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include<iostream>
#include<cmath>
using namespace std;

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);  // opengl_frame glfw_frame new_frame，知道为啥有这么多JB帧了吧
}
/*
 *
 * 这里我们检查用户是否按下了返回键(Esc)（如果没有按下，glfwGetKey将会返回GLFW_RELEASE。
 * 如果用户的确按下了返回键，我们将通过glfwSetwindowShouldClose使用把WindowShouldClose属性设置为 true的方法关闭GLFW。
 *
 * */
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glsl 渲染语言，这和C++调用Matlab差不多
const char *vertexShaderSource = "#version 330 core\n"
                                 "layout (location = 0) in vec3 aPos;\n"
                                 "void main()\n"
                                 "{\n"
                                 "   gl_Position = vec4(aPos, 1.0);\n"
                                 "}\0";

const char *fragmentShaderSource = "#version 330 core\n"
                                   "out vec4 FragColor;\n"
                                   "uniform vec4 ourColor;\n"
                                   "void main()\n"
                                   "{\n"
                                   "   FragColor = ourColor;\n"
                                   "}\n\0";

int main()
{
    // <1>、初始化GLFW
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // opengl3.3
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // 只用核心通用模块

    // <2>、glfw窗口创建
    GLFWwindow* window = glfwCreateWindow(800, 600, "shiruiyu", NULL, NULL);
    if (window == NULL)
    {
        cout << "fuck" << endl;
        glfwTerminate(); // Release
        return -1;
    }
    glfwMakeContextCurrent(window); // 通知GLFW将我们窗口的上下文设置为当前线程的主上下文了。
    /*
     * 告诉OpenGL渲染窗口的尺寸大小
     * OpenGL坐标范围只为-1到1，因此我们事实上将(-1到1)范围内的坐标映射到(0, 800)和(0, 600)。
     * */
    // 对窗口注册一个回调函数(Callback Function)，它会在每次窗口大小被调整的时候被调用
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    /*
     * <3>、利用glad加载所有OpenGL函数地址
     * GLAD是用来管理OpenGL的函数指针的，所以在调用任何OpenGL的函数之前我们需要初始化GLAD
     * */
    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress))
    {
        cout << "Failed to init GLAD" << endl;
        return -1;
    }
    // <4>、构建、编译shader program
    // 创建顶点渲染器，vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // 验证渲染器是否正常
    int success = 0;
    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;
    }
    // 创建线段渲染器，fragment shader
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // 验证渲染器是否正常
    success = 0;
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // 链接渲染器，link shaders
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // 检测链接错误
    success = 0;
    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, // left
            0.5f, -0.5f, 0.0f, // right
            0.0f,  0.5f, 0.0f  // top
    };
    unsigned int VBO, VAO; // ???
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    // 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);

    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);

    // 循环渲染
    while(!glfwWindowShouldClose(window)) // 检查一次GLFW是否被要求退出
    {
        // 输入
        processInput(window);

        // 渲染指令
        // 清除颜色缓冲
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        // 激活着色器
        glUseProgram(shaderProgram);

        // 更新uniform颜色
        float timeValue = glfwGetTime();
        float greenValue = std::sin(timeValue)/2.0f + 0.5f;
        int vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor");
        glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f);


        // 画第一个三角形

        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);// Primitive:GL_POINTS、GL_TRIANGLES、GL_LINE_STRIP





        // 检查并调用事件，交换缓冲
        glfwPollEvents(); // 检查有没有触发什么事件（比如键盘输入、鼠标移动等）、更新窗口状态，并调用对应的回调函数（可以通过回调方法手动设置）。
        glfwSwapBuffers(window); // 函数会交换颜色缓冲（它是一个储存着GLFW窗口每一个像素颜色值的大缓冲），它在这一迭代中被用来绘制，并且将会作为输出显示在屏幕上。

    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);

    // release
    glfwTerminate();

    return 0;
}