Qt下加载图片，在图片上绘制多边形，移动鼠标拉伸多边形

本实例是绘制梯形，拖动四个顶点可以拉伸图形

编译环境为 Win7–Qt5.4

1.新建Application工程项目,命名为TiXing,基类选择QWidget;

2.在widget.h的头文件中添加以下声明：

private:
int j;
int m_dragging;
int X[4]={50,200,300,50},Y[4]={100,100,200,200};
protected:
void mouseReleaseEvent(QMouseEvent*event);
void mousePressEvent(QMouseEvent*event);
void mouseMoveEvent(QMouseEvent*event);
void paintEvent(QPaintEvent *event);

3.然后再widget.cpp文件中添加头文件：

#include <QPainter>
#include <QMouseEvent>
#include <QWidget>
#include <QPen>
#include<QDebug>

继续添加函数定义：

void Widget::paintEvent(QPaintEvent *event)
{

QPainter paint(this);
QImage image;
image.load("../POLYGON/MyDrawing/luo.jpg");
qDebug() << image.size() << image.format() <<  image.depth();
paint.drawImage(QPoint(0, 0), image);
paint.setPen(QPen(Qt::blue,5));
for(int i=0;i<4;i++)
paint.drawPoint(X[i],Y[i]);
paint.setPen(Qt::red);
QPolygon pts;
pts.setPoints(4, X[0],Y[0], X[1],Y[1], X[2],Y[2],X[3],Y[3]);
paint.drawConvexPolygon(pts);

}
void Widget::mouseReleaseEvent(QMouseEvent *event)
{
m_dragging = 0;
}
void Widget::mousePressEvent(QMouseEvent *event)
{
for(int i=0;i<4;i++)
{
if(event->pos().x()==X[i]&&event->pos().y()==Y[i])
{  m_dragging = 1;
j=i;
break;
}
else continue;
}
}
void Widget::mouseMoveEvent(QMouseEvent *event)
{
if (m_dragging==1)
{
X[j]=event->pos().x();
Y[j]=event->pos().y();
update();
}
}

4.运行结果如下：



附上文件代码：

widget.h
-------------------------------------------------------
#ifndef WIDGET_H
#define WIDGET_H
#include <QWidget>
namespace Ui
{
class Widget;
}

class Widget : public QWidget
{
Q_OBJECT

public:
explicit Widget(QWidget *parent = 0);
~Widget();

private:
Ui::Widget *ui;
// int a;
// int b;
int j;
int m_dragging;
int X[4]={50,200,300,50},Y[4]={100,100,200,200};
protected:
void mouseReleaseEvent(QMouseEvent*event);
void mousePressEvent(QMouseEvent*event);
void mouseMoveEvent(QMouseEvent*event);
void paintEvent(QPaintEvent *event);

};

#endif // WIDGET_H

widget.cpp
-------------------------------------------------------
#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
#include <QMouseEvent>
#include <QWidget>
#include <QPen>
#include<QDebug>
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
m_dragging = 0;
ui->setupUi(this);
resize(500,514);
setWindowTitle(tr("polygon"));
}

Widget::~Widget()
{
delete ui;
}
void Widget::paintEvent(QPaintEvent *event)
{
QPainter paint(this);
QImage image;
image.load("../POLYGON/MyDrawing/luo.jpg");
qDebug() << image.size() << image.format() << image.depth();
paint.drawImage(QPoint(0, 0), image);
paint.setPen(QPen(Qt::blue,5));
for(int i=0;i<4;i++)
paint.drawPoint(X[i],Y[i]);
paint.setPen(Qt::red);
QPolygon pts;
pts.setPoints(4, X[0],Y[0], X[1],Y[1], X[2],Y[2],X[3],Y[3]);
paint.drawConvexPolygon(pts);
}
void Widget::mouseReleaseEvent(QMouseEvent *event)
{
m_dragging = 0;
}
void Widget::mousePressEvent(QMouseEvent *event)
{
for(int i=0;i<4;i++)
{
if(event->pos().x()==X[i]&&event->pos().y()==Y[i])
{  m_dragging = 1;
j=i;
break;
}
//else continue;
}
}
void Widget::mouseMoveEvent(QMouseEvent *event)
{
if (m_dragging==1)
{
X[j]=event->pos().x();
Y[j]=event->pos().y();
update();
}
}