46.Qt 使用OpenGL绘制立方体

main.cpp

#include <QApplication>
#include <iostream>

#include "vowelcube.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    if (!QGLFormat::hasOpenGL()) {
        std::cerr << "This system has no OpenGL support" << std::endl;
        return ;
    }

    VowelCube cube;
    cube.setWindowTitle(QObject::tr("Vowel Cube"));
    cube.setMinimumSize(, );
    cube.resize(, );
    cube.show();

    return app.exec();
}

vowelcube.h

#ifndef VOWELCUBE_H
#define VOWELCUBE_H

#include <QGLWidget>
#include <QRadialGradient>

//使用OpenGL绘制立方体，使用QPainter绘制背景
//的渐变，接着使用renderText（）绘制立方体角上的8个
//元音字母，最后使用QPainter和QTextDocument绘制图例。
//用户可以单击并拖动鼠标来旋转立方体，并且可以使用鼠标滚轮进行放大或缩小
class VowelCube : public QGLWidget
{
    Q_OBJECT

public:
    VowelCube(QWidget *parent = );
    ~VowelCube();

protected:
    void paintEvent(QPaintEvent *event);
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void wheelEvent(QWheelEvent *event);

private:
    void createGradient();
    void createGLObject();
    void drawBackground(QPainter *painter);
    void drawCube();
    void drawLegend(QPainter *painter);

    GLuint glObject;
    QRadialGradient gradient;
    GLfloat rotationX;
    GLfloat rotationY;
    GLfloat rotationZ;
    GLfloat scaling;
    QPoint lastPos;
};

#endif

vowelcube.cpp

 #include <QtGui>
 #include <QtOpenGL>
 #include <cmath>

 #ifndef GL_MULTISAMPLE
 #define GL_MULTISAMPLE 0x809D
 #endif

 #include "vowelcube.h"

 VowelCube::VowelCube(QWidget *parent)
     : QGLWidget(parent)
 {
     //调用setFormat（）使OpenGL的显示描述表支持饭走样。
     setFormat(QGLFormat(QGL::SampleBuffers));

     //初始化私有变量
     rotationX = -38.0;
     rotationY = -58.0;
     rotationZ = 0.0;
     scaling = 1.0;

     //设置填充背景的QRadialGradient
     createGradient();
     //创建OpenGL立方体对象
     createGLObject();

     setAutoBufferSwap( false );
     setAutoFillBackground( false );
 }

 VowelCube::~VowelCube()
 {
     makeCurrent();
     //删除构造函数创建的OpenGL立方体对象
     glDeleteLists(glObject, );
 }

 //绘制,在paintEvent()中创建一个QPainter,在进行纯OpenGL操作时
 //保存和恢复其状态。
 //QPainter的构造函数(或者QPainter::begin())自动调用glClear
 //除非预先调用窗口部件的setAutoFillBackground(false)
 //QPainter的析构函数（或者QPainter::end()）自动调用QGLWidget::swapBuffers()
 //切换可见缓存和离屏缓存，除非预先调用setAutoBufferSwap(false).
 //当QPainter被激活，我们可以交叉使用纯OpenGL命令，只要在执行纯OpenGL命令之前保存OpenGL状态，之后恢复OpenGL状态
 void VowelCube::paintEvent(QPaintEvent * /* event */)
 {
     QPainter painter( this );
     //绘制背景
     drawBackground( &painter );
     //背景绘制结束
     painter.end( );
     //绘制立方体
     drawCube();
     //绘制开始
     painter.begin(this);
     //使用HTML文字设置QTextDocument对象
     drawLegend(&painter);
     painter.end( );
     swapBuffers( );
 }

 //鼠标按下事件
 void VowelCube::mousePressEvent(QMouseEvent *event)
 {
     lastPos = event->pos();
 }

 //鼠标移动事件
 void VowelCube::mouseMoveEvent(QMouseEvent *event)
 {
     GLfloat dx = GLfloat(event->x() - lastPos.x()) / width();
     GLfloat dy = GLfloat(event->y() - lastPos.y()) / height();

     if (event->buttons() & Qt::LeftButton) {
         rotationX +=  * dy;
         rotationY +=  * dx;
         update();
     } else if (event->buttons() & Qt::RightButton) {
         rotationX +=  * dy;
         rotationZ +=  * dx;
         update();
     }
     lastPos = event->pos();
 }

 //鼠标滚动的事件，调用update
 void VowelCube::wheelEvent(QWheelEvent *event)
 {
     double numDegrees = -event->delta() / 8.0;
     double numSteps = numDegrees / 15.0;
     scaling *= std::pow(1.125, numSteps);
     update();
 }

 //使用蓝色渐变色设置QRadialGradient
 void VowelCube::createGradient()
 {
     //确保指定的中心和焦点坐标根据窗口部件大小进行调整
     gradient.setCoordinateMode(QGradient::ObjectBoundingMode);
     //位置用0和1之间的浮点数表示，0对应焦点坐标，1对应圆的边缘
     gradient.setCenter(0.45, 0.50);
     gradient.setFocalPoint(0.40, 0.45);
     gradient.setColorAt(0.0, QColor(, , ));
     gradient.setColorAt(0.4, QColor(, , ));
     gradient.setColorAt(0.8, QColor(, , ));
 }

 //创建OpenGL列表，该列表保存绘制的立方体的边。
 void VowelCube::createGLObject()
 {
     makeCurrent();

     glShadeModel(GL_FLAT);

     glObject = glGenLists();
     glNewList(glObject, GL_COMPILE);
     qglColor(QColor(, , ));
     glLineWidth(1.0);

     glBegin(GL_LINES);
     glVertex3f(+1.0, +1.0, -1.0);
     glVertex3f(-1.0, +1.0, -1.0);
     glVertex3f(+1.0, -1.0, -1.0);
     glVertex3f(-1.0, -1.0, -1.0);
     glVertex3f(+1.0, -1.0, +1.0);
     glVertex3f(-1.0, -1.0, +1.0);
     glEnd();

     glBegin(GL_LINE_LOOP);
     glVertex3f(+1.0, +1.0, +1.0);
     glVertex3f(+1.0, +1.0, -1.0);
     glVertex3f(+1.0, -1.0, -1.0);
     glVertex3f(+1.0, -1.0, +1.0);
     glVertex3f(+1.0, +1.0, +1.0);
     glVertex3f(-1.0, +1.0, +1.0);
     glVertex3f(-1.0, +1.0, -1.0);
     glVertex3f(-1.0, -1.0, -1.0);
     glVertex3f(-1.0, -1.0, +1.0);
     glVertex3f(-1.0, +1.0, +1.0);
     glEnd();

     glEndList();
 }

 void VowelCube::drawBackground(QPainter *painter)
 {
     painter->setPen(Qt::NoPen);
     painter->setBrush(gradient);
     painter->drawRect(rect());
 }

 //绘制立方体
 void VowelCube::drawCube()
 {
     glPushAttrib(GL_ALL_ATTRIB_BITS);

     glMatrixMode(GL_PROJECTION);
     glPushMatrix();
     glLoadIdentity();
     GLfloat x = 3.0 * GLfloat(width()) / height();
     glOrtho(-x, +x, -3.0, +3.0, 4.0, 15.0);

     glMatrixMode(GL_MODELVIEW);
     glPushMatrix();
     glLoadIdentity();
     glTranslatef(0.0, 0.0, -10.0);
     glScalef(scaling, scaling, scaling);

     glRotatef(rotationX, 1.0, 0.0, 0.0);
     glRotatef(rotationY, 0.0, 1.0, 0.0);
     glRotatef(rotationZ, 0.0, 0.0, 1.0);

     //设置反走样
     glEnable(GL_MULTISAMPLE);

     //绘制立方体
     glCallList(glObject);

     //设置文字颜色和字体
     setFont(QFont("Times", ));
     qglColor(QColor(, , ));

     //绘制字符，renderText使文字不变形
     renderText(+1.1, +1.1, +1.1, QChar('a'));
     renderText(-1.1, +1.1, +1.1, QChar('e'));
     renderText(+1.1, +1.1, -1.1, QChar('o'));
     renderText(-1.1, +1.1, -1.1, QChar(0x00F6));
     renderText(+1.1, -1.1, +1.1, QChar(0x0131));
     renderText(-1.1, -1.1, +1.1, QChar('i'));
     renderText(+1.1, -1.1, -1.1, QChar('u'));
     renderText(-1.1, -1.1, -1.1, QChar(0x00FC));

     glMatrixMode(GL_MODELVIEW);
     glPopMatrix();

     glMatrixMode(GL_PROJECTION);
     glPopMatrix();

     glPopAttrib();
 }

 //使用HTML文字设置QTextDocument对象，在半透明的蓝色矩形上绘制它们
 void VowelCube::drawLegend(QPainter *painter)
 {
     const int Margin = ;
     const int Padding = ;

     QTextDocument textDocument;
     textDocument.setDefaultStyleSheet("* { color: #FFEFEF }");
     textDocument.setHtml("<h4 align=\"center\">Vowel Categories</h4>"
                          "<p align=\"center\"><table width=\"100%\">"
                          "<tr><td>Open:<td>a<td>e<td>o<td>&ouml;"
                          "<tr><td>Close:<td>ı<td>i<td>u<td>&uuml;"
                          "<tr><td>Front:<td>e<td>i<td>&ouml;<td>&uuml;"
                          "<tr><td>Back:<td>a<td>ı<td>o<td>u"
                          "<tr><td>Round:<td>o<td>&ouml;<td>u<td>&uuml;"
                          "<tr><td>Unround:<td>a<td>e<td>ı<td>i"
                          "</table>");
     textDocument.setTextWidth(textDocument.size().width());

     QRect rect(QPoint(, ), textDocument.size().toSize()
                              + QSize( * Padding,  * Padding));
     painter->translate(width() - rect.width() - Margin,
                        height() - rect.height() - Margin);
     painter->setPen(QColor(, , ));
     painter->setBrush(QColor(, , , ));
     painter->drawRect(rect);

     painter->translate(Padding, Padding);
     textDocument.drawContents(painter);
 }