Hello Triangle_练习三

创建两个着色器程序，第二个程序使用一个不同的片段着色器，输出黄色；再次绘制这两个三角形，让其中一个输出为黄色

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

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
}
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}
const char *vertexShaderSource = "#version 330 core
"
"layout (location = 0) in vec3 aPos;
"
"void main()
"
"{
"
"   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
"
"}";
const char *fragmentShaderSource1 = "#version 330 core
"
"out vec4 FragColor;
"
"void main()
"
"{
"
"   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);
"
"}
";
const char *fragmentShaderSource2 = "#version 330 core
"
"out vec4 FragColor;
"
"void main()
"
"{
"
"   FragColor = vec4(1.0f, 1.0f, 0.0f, 1.0f);
"
"}
";

int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    //glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

    GLFWwindow* window = glfwCreateWindow(800, 600, "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);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    //vertex shader
    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
" << infoLog << std::endl;
    }

    //first fragment shader
    int fragmentShader1 = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader1, 1, &fragmentShaderSource1, NULL);
    glCompileShader(fragmentShader1);
    
    //second fragment shader
    int fragmentShader2 = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader2, 1, &fragmentShaderSource2, NULL);
    glCompileShader(fragmentShader2);

    // first link shaders
    int shaderProgram1 = glCreateProgram();
    glAttachShader(shaderProgram1, vertexShader);
    glAttachShader(shaderProgram1, fragmentShader1);
    glLinkProgram(shaderProgram1);

    //second link shaders
    int shaderProgram2 = glCreateProgram();
    glAttachShader(shaderProgram2, vertexShader);
    glAttachShader(shaderProgram2, fragmentShader2);
    glLinkProgram(shaderProgram2);

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader1);
    glDeleteShader(fragmentShader2);

    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 VBO[2], VAO[2];
    glGenVertexArrays(2, VAO);
    glGenBuffers(2, VBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO[0]);
    glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(firstTriangle), firstTriangle, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    glBindVertexArray(VAO[1]);
    glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(secondTriangle), secondTriangle, 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);

    while (!glfwWindowShouldClose(window))
    {
        //输入
        processInput(window);

        //渲染指令
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // draw our first triangle
        glUseProgram(shaderProgram1);
        glBindVertexArray(VAO[0]); // 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);

        glUseProgram(shaderProgram2);
        glBindVertexArray(VAO[1]);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        // glBindVertexArray(0); // no need to unbind it every time 

        //检查并调用事件，交换缓冲
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    glDeleteVertexArrays(2, VAO);
    glDeleteBuffers(2, VBO);

    glfwTerminate();
    return 0;
}

2019/11/26