OpenGL现代编程第二课——第一个多边形

#include <QOpenGLWidget>
#include <QOpenGLExtraFunctions>

class MyGLWidget : public QOpenGLWidget, protected QOpenGLExtraFunctions
{
    Q_OBJECT

public:
    MyGLWidget(QWidget *parent = nullptr);

    ~MyGLWidget();

protected:
    virtual void initializeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();

private:
//顶点缓冲对象 Vertex Buffer Object，VBO，教程中第一个出现的OpenGL对象
    GLuint VBO;                
    GLuint VAO;

    GLuint EBO;

    GLuint m_shaderProgram;    //着色器程序对象

//着色器语言GLSL(OpenGL Shading Language)编写的顶点着色器
static const char *vertexShaderSource =
        "#version 330 core\n"
        "layout(location = 0) in vec3 aPos;\n"
        "void main(){\n"
        "  gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
        "}\n\0";


//着色器语言GLSL(OpenGL Shading Language)编写的片段着色器
static const char *fragmentShaderSource =
        "#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main(){\n"
        "   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
        "}\n\0";

#define TRIANGLE
//#define RECTANGLE

MyGLWidget::MyGLWidget(QWidget *parent)
    : QOpenGLWidget(parent)
{

}

MyGLWidget::~MyGLWidget()
{

}

void MyGLWidget::initializeGL()
{

    this->initializeOpenGLFunctions();          //重要！一定要在调用任何gl函数前调用该函数！！

    //着色器部分
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);            //创建顶点着色器对象
    glShaderSource(GLuint(vertexShader), 1, &vertexShaderSource, nullptr); //着色器源码附加到着色器对象
    glCompileShader(GLuint(vertexShader));                                 //编译

    int is_success;      //检查是否编译成功，未成功则需返回错误
    char infoLog[512];
    glGetShaderiv(GLuint(vertexShader), GL_COMPILE_STATUS, &is_success);
    if (!is_success)
    {
        glGetShaderInfoLog(GLuint(vertexShader), 512, nullptr, infoLog);
        qDebug() << "ERROR::SHADER::VERTEX::COMPILATION_FAILED" << infoLog ;
    }


    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);  //创建片段着色器对象，与顶点着色器相似
    glShaderSource(GLuint(fragmentShader), 1, &fragmentShaderSource, nullptr);
    glCompileShader(GLuint(fragmentShader));

    glGetShaderiv(GLuint(fragmentShader), GL_COMPILE_STATUS, &is_success);
    if (!is_success)
    {
        glGetShaderInfoLog(GLuint(fragmentShader), 512, nullptr, infoLog);
        qDebug() << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED" << infoLog;
    }


    m_shaderProgram = glCreateProgram();                         //创建着色器程序对象
    glAttachShader(m_shaderProgram, GLuint(vertexShader));
    glAttachShader(m_shaderProgram, GLuint(fragmentShader));
    glLinkProgram(m_shaderProgram);                     //之前编译的着色器附加到程序对象上

glGetProgramiv(m_shaderProgram, GL_LINK_STATUS, &is_success);
    if (!is_success) {
        glGetProgramInfoLog(m_shaderProgram, 512, nullptr, infoLog);
        qDebug() << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog ;
    }

    glDeleteShader(vertexShader);        //着色器对象链接到程序对象以后，删除着色器对象
    glDeleteShader(fragmentShader);

    //VAO，VBO数据部分

#ifdef TRIANGLE
    GLfloat vertices[] = {
        -0.5f, -0.5f, 0.0f, // left
        0.5f, -0.5f, 0.0f,  // right
        0.0f,  0.5f, 0.0f   // top
    };
#else                                      //绘制矩形
    GLfloat 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[] = { // 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
    };
#endif
    //两个参数，第一个为需要创建的缓存数量。第二个为用于存储单一ID或多个ID的GLuint变量或数组的地址
    glGenVertexArrays(1, &VAO);          
    glGenBuffers(1, &VBO);               //顶点缓冲对象处理
    glGenBuffers(1, &EBO);
    glBindVertexArray(VAO);
    //使用glBindBuffer函数把新创建的缓冲绑定到GL_ARRAY_BUFFER目标上
    glBindBuffer(GL_ARRAY_BUFFER, VBO);  
    //之前定义的顶点数据复制到缓冲的内存中
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);      
#ifdef RECTANGLE
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
#endif
    //glVertexAttribPointer函数告诉OpenGL该如何解析顶点数据（应用到逐个顶点属性上）
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), nullptr);  
    glEnableVertexAttribArray(0);  //以顶点属性位置值作为参数，启用顶点属性；顶点属性默认是禁用的

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

}

void MyGLWidget::resizeGL(int w, int h)
{
    glViewport(0, 0, w, h);
}

void MyGLWidget::paintGL()
{
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(m_shaderProgram);             //激活程序对象
    glBindVertexArray(VAO);   
#ifdef TRIANGLE
    glDrawArrays(GL_TRIANGLES, 0, 3);
#else                                         //绘制矩形
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);
#endif
//    glUseProgram(0);
}