1-4EBO画矩形_哔哩哔哩_bilibili

可以绘制两个三角形来组成一个矩形（OpenGL主要处理三角形）

直接画两个三角形：

#include "openglwidget.h"
#include <QDebug>

unsigned int VBO,VAO;
unsigned int shaderProgram;

//顶点着色器
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";
//片段着色器
const char* fragmentShaderSource="#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main()\n"
        "{\n"
        "FragColor=vec4(0.3f,0.5f,0.2f,0.2f);\n"
        "}\0";

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

}

void OpenGLWidget::initializeGL()
{
    initializeOpenGLFunctions();

    float vertices[]={
        0.5f, 0.5f, 0.0f,   // 右上角
        0.5f, -0.5f, 0.0f,  // 右下角
        -0.5f, 0.5f, 0.0f,  // 左上角
        // 第二个三角形
        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
    };
    //顶点数组
    glGenVertexArrays(1,&VAO);
    //顶点缓冲对象
    glGenBuffers(1,&VBO);

    //绑定顶点数组
    glBindVertexArray(VAO);
    //绑定顶点缓冲对象
    glBindBuffer(GL_ARRAY_BUFFER,VBO);

    //把三角形相关数据复制到缓冲内存中
    glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);
    //第二个参数：数据的大小（字节为单位）
    //第三个参数：数据指针


    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,3*sizeof(float),(void *)0);
    glEnableVertexAttribArray(0);

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


    unsigned int vertexShader=glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader,1,&vertexShaderSource,NULL);
    glCompileShader(vertexShader);

    int  success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);

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

    unsigned int fragmentShader=glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader,1,&fragmentShaderSource,NULL);
    glCompileShader(fragmentShader);

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

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

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

}

void OpenGLWidget::resizeGL(int w, int h)
{

}

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

    glUseProgram(shaderProgram);

    glBindVertexArray(VAO);
    glDrawArrays(GL_TRIANGLES,0,6);
}

使用线条填充：

void OpenGLWidget::initializeGL()

{

glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);//使用线条填充

}

使用VBO,EBO,VAO来画两个三角形

#include "openglwidget.h"
#include <QDebug>

unsigned int VBO,VAO,EBO;
unsigned int shaderProgram;

//顶点着色器
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";
//片段着色器
const char* fragmentShaderSource="#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main()\n"
        "{\n"
        "FragColor=vec4(0.3f,0.5f,0.2f,0.2f);\n"
        "}\0";

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

}

void OpenGLWidget::initializeGL()
{
    initializeOpenGLFunctions();

    float vertices[] = {
        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!
        // 此例的索引(0,1,2,3)就是顶点数组vertices的下标，
        // 这样可以由下标代表顶点组合成矩形

        0, 1, 3, // 第一个三角形
        1, 2, 3  // 第二个三角形
    };
    //顶点数组
    glGenVertexArrays(1,&VAO);
    //顶点缓冲对象
    glGenBuffers(1,&VBO);
    glGenBuffers(1,&EBO);

    //绑定顶点数组
    glBindVertexArray(VAO);
    //绑定顶点缓冲对象
    glBindBuffer(GL_ARRAY_BUFFER,VBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,EBO);

    //把相关数据复制到缓冲内存中
    glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);
    //第二个参数：数据的大小（字节为单位）
    //第三个参数：数据指针
    glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(indices),indices,GL_STATIC_DRAW);


    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,3*sizeof(float),(void *)0);
    glEnableVertexAttribArray(0);

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


    unsigned int vertexShader=glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader,1,&vertexShaderSource,NULL);
    glCompileShader(vertexShader);

    int  success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);

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

    unsigned int fragmentShader=glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader,1,&fragmentShaderSource,NULL);
    glCompileShader(fragmentShader);

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

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

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);//使用线条填充


}

void OpenGLWidget::resizeGL(int w, int h)
{

}

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

    glUseProgram(shaderProgram);

    glBindVertexArray(VAO);
    //VAO知道VBO和EBO的情况

    glDrawElements(GL_TRIANGLES,6,GL_UNSIGNED_INT,0);
}

VAO会记录EBO的绑定和解绑，不会记录VBO的绑定和解绑。