使用Qt进行OpenGL开发-绘制简单矩形

Qt中自带OpenGL模块可以用来进行三维开发,下面介绍一下在Qt中进行OpenGL开发的一些简单Demo。OpenGL的最小图元是三角形。矩形则由两个三角形组成。通过四个顶点坐标和顶点的索引确定两个三角形，从而组成一个矩形。代码采用的是Qt的Opengl模块，管道编程采用的是GLSL语言。

在头文件中需要包含Qt对应的模块头文件,对应的头文件代码如下。

opengl.h

#ifndef OPENGL_H
#define OPENGL_H

#include 
#include 
#include 
#include 
#include 
#include 

class openGL : public QGLWidget, protected QGLFunctions
{
    Q_OBJECT

public:
    openGL(QWidget *parent = 0);
    ~openGL();
protected:
    void initializeGL();             //初始化OpenGL
    void resizeGL(int w, int h);     //调整oeenGL的显示窗口
    void paintGL();                  //绘制opengl图像
private:
    void InitShader();
    void InitBuffer();
private:
    QGLShaderProgram shader;
    QGLBuffer* vertexBuffer;
    QGLBuffer* indexBuffer;
    float viewPortWidth;
    float viewPortHeight;

};
#endif // OPENGL_H

opengl.cpp

#include "opengl.h"

QString vertexShaderSource =
"#version 330 core\n\
layout (location = 0) in vec3 aPos;\n\
void main()\n\
{\n\
gl_Position = vec4(aPos, 1.0);\n\
}";
QString fragmentShaderSource =
"#version 330 core\n\
out vec4 FragColor;\n\
void main()\n\
{\n\
FragColor = vec4(1.0f, 0.0f, 0.0f, 1.0f);\n\
}";

float vertices[] = {
    0.5f, 0.5f, 0.0f,   
    0.5f, -0.5f, 0.0f,    
   -0.5f, -0.5f, 0.0f,
   -0.5f,  0.5f, 0.0f
   };

unsigned int indices[] =
{
    0, 1, 3,
    1, 2, 3
};

openGL::openGL(QWidget *parent)
    : QGLWidget(parent)
    ,viewPortWidth(300.0)
    ,viewPortHeight(300.0)
{
}

openGL::~openGL()
{
    delete vertexBuffer;
    delete indexBuffer;
}

void openGL::initializeGL()
{
    glViewport(0, 0, viewPortWidth, viewPortHeight);
    glEnable(GL_DEPTH_TEST);
    initializeGLFunctions(); 
    InitShader();
    InitBuffer();
}

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

void openGL::paintGL()
{
    resize(viewPortWidth, viewPortHeight);
    glViewport(0, 0, viewPortWidth, viewPortHeight);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    indexBuffer->bind();
    shader.bind();
    shader.enableAttributeArray("aPos");
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
    shader.disableAttributeArray("aPos");
    shader.release();
    indexBuffer->release();
}
void openGL::InitShader()
{
    shader.addShaderFromSourceCode(QGLShader::Vertex, vertexShaderSource);
    shader.addShaderFromSourceCode(QGLShader::Fragment, fragmentShaderSource);
    shader.link();
}

void openGL::InitBuffer()
{
    vertexBuffer = new QGLBuffer(QGLBuffer::VertexBuffer);
    indexBuffer = new QGLBuffer(QGLBuffer::IndexBuffer);

    shader.bind();
    vertexBuffer->create();
    vertexBuffer->bind();
    vertexBuffer->allocate(vertices, sizeof(vertices));
    vertexBuffer->setUsagePattern(QGLBuffer::StaticDraw);
    shader.setAttributeBuffer("aPos", GL_FLOAT, 0, 3, 12);
    vertexBuffer->release();
    shader.release();

    indexBuffer->create();
    indexBuffer->bind();
    indexBuffer->allocate(indices, sizeof(indices));
    indexBuffer->setUsagePattern(QGLBuffer::StaticDraw);
    indexBuffer->release();
}

需要注意的是qt中opengl对应的显示方法都在QGLWidget中其它的操作方法都在QGLFunctions模块中,所以自定义的模块一定要继承这两个类。

对应的显示效果如下图所示：