Qt OpenGL 绘制三角形（一）

一、效果图

二、代码

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QDebug>
#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QOpenGLShaderProgram>
#include <QMatrix4x4>

class Widget : public QOpenGLWidget, protected QOpenGLFunctions
{
public:
    Widget(QWidget *parent = nullptr);
    ~Widget();
protected:
    void initializeGL();
    void paintGL();
    void resizeGL(int w, int h);

private:
    QOpenGLShaderProgram *program;
    GLuint programId;
    GLint matrixLocation,vertexLocation,clorLocation;
    int vVerticesLen,triIndexLen,colorsLen;
    GLuint verVbo,indexVbo,colorVbo;
    QMatrix4x4 projection;
};
#endif // WIDGET_H

#include "widget.h"

//三角形顶点坐标
GLfloat vertex[] = {
    -0.5f, 0.0f,
    0.5f, 0.0f,
    0.0f, 0.5f,
};

//三角形顶点索引
GLuint triIndexs[] = {0, 1, 2};

//三角形顶点颜色
GLfloat colors[] = {1.0f, 0.0f, 0.0f, 1.0f,
                    0.0f, 1.0f, 0.0f, 1.0f,
                    0.0f, 0.0f, 1.0f, 1.0f,
                   };

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

}

Widget::~Widget()
{

}

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

    program = new QOpenGLShaderProgram(this);

    if(!program->addShaderFromSourceFile(QOpenGLShader::Vertex, "E:/opengl/opengl/vertexshader.vert")){
        qDebug()<<"vert fail";
        return;
    }
    if(!program->addShaderFromSourceFile(QOpenGLShader::Fragment, "E:/opengl/opengl/fragmentshader.frag")){
        return;
    }
    if(!program->link()){
        return;
    }
    if(!program->bind()){
        return;
    }

    // 获取shaderprogram的id号，然后可以通过id号获取一些属性...
    programId = program->programId();

    // 从shaderprogram里面获取变量标识
    matrixLocation = glGetUniformLocation(programId, "matrix");
    vertexLocation = glGetAttribLocation(programId, "vPosition");
    clorLocation  = glGetAttribLocation(programId, "vColor");

    // 计算获得数组长度
    vVerticesLen = sizeof(vertex)/sizeof(GLfloat);
    triIndexLen = sizeof(triIndexs)/sizeof(GLuint);
    colorsLen = sizeof(colors)/sizeof(GLfloat);

    // 初始化顶点buffer并装载数据到显存
    glGenBuffers(1, &verVbo);
    glBindBuffer(GL_ARRAY_BUFFER, verVbo);
    glBufferData(GL_ARRAY_BUFFER, vVerticesLen * sizeof(GLfloat), vertex, GL_STATIC_DRAW);

    // 初始化索引buffer并装载数据到显存
    glGenBuffers(1, &indexVbo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVbo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, triIndexLen * sizeof(GLuint), triIndexs, GL_STATIC_DRAW);

    // 初始化颜色buffer并装载数据到显存
    glGenBuffers(1, &colorVbo);
    glBindBuffer(GL_ARRAY_BUFFER, colorVbo);
    glBufferData(GL_ARRAY_BUFFER, colorsLen * sizeof(GLfloat), colors, GL_STATIC_DRAW);
}

void Widget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

    // shader传入模型视图矩阵 projection可以理解为建立了一个坐标系空间，可以再这个空间内设置图形
    glUniformMatrix4fv(matrixLocation, 1, GL_FALSE, projection.data());

    // shader绑定并启用颜色数组buffer
    glBindBuffer(GL_ARRAY_BUFFER,colorVbo);
    glVertexAttribPointer(clorLocation, 4, GL_FLOAT, GL_FALSE, 0, 0);
    glEnableVertexAttribArray(clorLocation);
    // 颜色值rgba，所以每四个float值作为一个颜色值，如果只是希望rgb，取三个值作为颜色值即可!


    // shader绑定并启用顶点数组buffer
    glBindBuffer(GL_ARRAY_BUFFER, verVbo);
    glVertexAttribPointer( vertexLocation, 2, GL_FLOAT, GL_FALSE, 0, 0);
    glEnableVertexAttribArray(vertexLocation);

    // shader绑定并顶点索引数组buffer - 索引无需启用
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,indexVbo);
    glDrawElements(GL_TRIANGLES, triIndexLen, GL_UNSIGNED_INT,0);

    // 解绑buffer、关闭启用顶点、颜色数组
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glDisableVertexAttribArray(vertexLocation);
    glDisableVertexAttribArray(clorLocation);
}


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

    // 模型矩阵重置
    projection.setToIdentity();
    // 透视投影
    qreal aspect = qreal(w) / qreal(h ? h : 1);
    projection.perspective(60.0f, aspect, 1.0f, 100.0f);
    // 增加了模型矩阵，需要做一定偏移量，保证物体刚开始渲染出来时可以被看到！
    projection.translate(0.0f, 0.0f, -2.0f);
}

vertexshader.vert

//vertexshader.vert
uniform mat4 matrix;
in vec4 vPosition;
in vec4 vColor;
out vec4 fColor;

void main(void)
{
    fColor = vColor;
    gl_Position = matrix * vPosition;
}

fragmentshader.frag

//fragmentshader.frag
in vec4 fColor;

void main(void)
{
    gl_FragColor = fColor;
}