Qt 绘制贝塞尔曲线例程

main.cpp

#include <QApplication>  
#include "mywidget.h"  
  
int main(int argc, char *argv[])  
{  
    QApplication a(argc, argv);  
  
    MyWidget w;  
    w.resize(300, 300);  
    w.show();  
  
    return a.exec();  
}  

mywidget.h

#ifndef MYWIDGET_H  
#define MYWIDGET_H  
  
#include <QWidget>  
#include <QLabel>  
#include <QMouseEvent>  
#include <QLabel>  
  
class MyWidget : public QWidget  
{  
    Q_OBJECT  
public:  
    explicit MyWidget(QWidget *parent = 0);  
  
    QLabel *startLabel;  
    QLabel *ctrlLabel1;  
    QLabel *ctrlLabel2;  
    QLabel *endLabel;  
  
    QLabel *ctrlLabel3;  
    QLabel *ctrlLabel4;  
    QLabel *endLabel2;  
  
    QWidget *selectedWidget;  
  
private:  
    void paintEvent(QPaintEvent *event);  
    void mousePressEvent(QMouseEvent *event);  
    void mouseMoveEvent(QMouseEvent *event);  
    void mouseReleaseEvent(QMouseEvent *event);  
  
};  
  
#endif // MYWIDGET_H  

mywidget.cpp

#include "mywidget.h"  
#include <QPainter>  
#include <QPainterPath>  
#include <QDebug>  
  
MyWidget::MyWidget(QWidget *parent) :  
    QWidget(parent)  
{  
  
    startLabel=new QLabel(this);  
    startLabel->resize(10, 10);  
    startLabel->setStyleSheet("QLabel{background-color:red;}");  
    startLabel->move(100, 110);  
  
    ctrlLabel1=new QLabel(this);  
    ctrlLabel1->resize(10, 10);  
    ctrlLabel1->setStyleSheet("QLabel{background-color:green;}");  
    ctrlLabel1->move(120, 120);  
  
    ctrlLabel2=new QLabel(this);  
    ctrlLabel2->resize(10, 10);  
    ctrlLabel2->setStyleSheet("QLabel{background-color:blue;}");  
    ctrlLabel2->move(140, 130);  
  
    endLabel=new QLabel(this);  
    endLabel->resize(10, 10);  
    endLabel->setStyleSheet("QLabel{background-color:black;}");  
    endLabel->move(160, 140);  
  
    ctrlLabel3=new QLabel(this);  
    ctrlLabel3->resize(10, 10);  
    ctrlLabel3->setStyleSheet("QLabel{background-color:yellow;}");  
    ctrlLabel3->move(180, 150);  
  
    ctrlLabel4=new QLabel(this);  
    ctrlLabel4->resize(10, 10);  
    ctrlLabel4->setStyleSheet("QLabel{background-color:cyan;}");  
    ctrlLabel4->move(200, 160);  
  
    endLabel2=new QLabel(this);  
    endLabel2->resize(10, 10);  
    endLabel2->setStyleSheet("QLabel{background-color:#AAAAEE;}");  
    endLabel2->move(220, 170);  
  
    selectedWidget=NULL;  
}  
  
  
void MyWidget::paintEvent(QPaintEvent *event)  
{  
    QPainter painter(this);  
    painter.setPen(Qt::black);  
    painter.drawLine(startLabel->pos(), ctrlLabel1->pos());  
    painter.drawLine(ctrlLabel2->pos(), endLabel->pos());  
    painter.drawLine(endLabel->pos(), ctrlLabel3->pos());  
    painter.drawLine(ctrlLabel4->pos(), endLabel2->pos());  
  
    QPainterPath myPath;  
    myPath.moveTo(startLabel->pos());  
    myPath.cubicTo(ctrlLabel1->pos(), ctrlLabel2->pos(), endLabel->pos());  
    myPath.cubicTo(ctrlLabel3->pos(), ctrlLabel4->pos(), endLabel2->pos());  
    painter.setPen(Qt::red);  
    painter.drawPath(myPath);  
}  
  
  
void MyWidget::mousePressEvent(QMouseEvent *event)  
{  
    QWidget *w=this->childAt(event->pos());  
    if(w==NULL) return;  
    if(w->inherits("QLabel")){  
        selectedWidget=w;  
    }  
}  
  
void MyWidget::mouseReleaseEvent(QMouseEvent *event)  
{  
    selectedWidget=NULL;  
}  
  
void MyWidget::mouseMoveEvent(QMouseEvent *event)  
{  
    if(selectedWidget!=NULL){  
        selectedWidget->move(event->pos());  
        this->update();  
    }  
}