OpenGL/OpenGL-03-Triangle/main.cpp

//
//  main.cpp
//  OpenGL-03-Triangle
//
//  Created by charles on 2020/7/19.
//  Copyright © 2020 charles. All rights reserved.
//

#include <iostream>

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

#define BUFFER_OFFSET(offset) ((GLvoid*)offset)

const int win_width = 800;
const int win_height = 600;

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void process_input(GLFWwindow *window);

//这里我们用enum来展示使用不同方法来渲染三角形
enum {
    ONLY_VBO = 0,
    VBO_VAO,
    VBO_EBO,
};
int current_factor = VBO_EBO;

unsigned int VBO;
unsigned int VAO;
unsigned int EBO;

int main(int argc, const char * argv[]) {
    // insert code here...
    std::cout << "Hello, World!\n";
    // 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
    
    GLFWwindow* window = glfwCreateWindow(win_width, win_height, "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;
    }
    
    //顶点着色器
    const char *vertexShaderSource = "#version 330 core\n"
    "layout (location = 9) in vec3 aPos;\n"
    "void main()\n"
    "{\n"
    "   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
    "}\0";
    //定义着色器并编译
    unsigned int vertexShader;
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    //检查编译错误
    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;
    }
    
    //片段着色器
    const char *fragmentShaderSource = "#version 330 core\n"
    "out vec4 fragColor;\n"
    "void main()\n"
    "{\n"
    "   fragColor = vec4(0.0f, 0.0f, 1.0f, 1.0f);\n"
    "}\n\0";
    unsigned int fragmentShader;
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    
    //着色器程序
    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);
    
    //三角形位置
    float vertices[] = {
        -0.5f, -0.5f, 0.0f,
         0.5f, -0.5f, 0.0f,
         0.0f,  0.5f, 0.0f
    };
    //四边形位置与索引
    float vertices2[] = {
        0.5f, 0.5f, 0.0f,   // 右上角
        0.5f, -0.5f, 0.0f,  // 右下角
        -0.5f, -0.5f, 0.0f, // 左下角
        -0.5f, 0.5f, 0.0f   // 左上角
    };

    unsigned int indices[] = { // 注意索引从0开始!
        0, 1, 3, // 第一个三角形
        1, 2, 3  // 第二个三角形
    };
    
    switch (current_factor) {
            
        case ONLY_VBO:
        {
            glGenBuffers(1, &VBO);
            glBindBuffer(GL_ARRAY_BUFFER, VBO);
            glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
            GLuint uPos = glGetAttribLocation( shaderProgram, "aPos" );
            glVertexAttribPointer( uPos, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), BUFFER_OFFSET(0) );
            glEnableVertexAttribArray( uPos );
        }
            break;
        case VBO_VAO:
        {
            //VAO
            glGenVertexArrays(1, &VAO);
            glBindVertexArray(VAO);
            
            //VBO
            glGenBuffers(1, &VBO);
            glBindBuffer(GL_ARRAY_BUFFER, VBO);
            glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
            //设置对缓冲区访问的步长为3以及相位为0，告诉着色器，这个数据输入到着色器的第一个(索引为0)输入变量，数据的长度是3个float
            GLuint uPos = glGetAttribLocation( shaderProgram, "aPos" );
            glVertexAttribPointer(uPos, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
            glEnableVertexAttribArray(uPos);
            
            //delete buffer and array
            glBindBuffer(GL_ARRAY_BUFFER, 0);
            glBindVertexArray(0);
        }
            
            break;
            
        case VBO_EBO:
        {
            //VAO
            glGenVertexArrays(1, &VAO);
            glBindVertexArray(VAO);
            
            //VBO
            glGenBuffers(1, &VBO);
            glBindBuffer(GL_ARRAY_BUFFER, VBO);
            glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);
            GLuint uPos = glGetAttribLocation( shaderProgram, "aPos" );
            glVertexAttribPointer(uPos, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
            glEnableVertexAttribArray(uPos);
            
            //EBO
            glGenBuffers(1, &EBO);
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
            glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
            
            //delete buffer array element
            glBindVertexArray(0);
            glBindBuffer(GL_ARRAY_BUFFER, 0);
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
        }
            break;
            
        default:
            break;
    }
    
    printf("VBO = %d \n", VBO);
    printf("VAO = %d \n", VAO);
    printf("EBO = %d \n", EBO);
    
    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        process_input(window);
        
        //render
        glClearColor(1.0f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        
        switch (current_factor) {
            case ONLY_VBO:
            {
                glUseProgram(shaderProgram);
                //这里留一个疑问，只用VBO可否画三角形？
                //B站看了一个视频说是不可以单独用；
                //查了资料，理论上讲应该是可行的，但是找了很多例子实验都不可以；
                glDrawArrays( GL_TRIANGLES, 0, 3 );
            }
                break;
            
            case VBO_VAO:
            {
                glUseProgram(shaderProgram);
                glBindVertexArray(VAO);
                glDrawArrays( GL_TRIANGLES, 0, 3 );
            }
                break;
                
            case VBO_EBO:
            {
                glUseProgram(shaderProgram);
                glBindVertexArray(VAO);
                glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
            }
                break;
                
            default:
                break;
        }
        

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    
    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 process_input(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.
    std::cout << width << "-----" << height << std::endl;
    glViewport(0, 0, width, height);
}