Qt 涂鸦画板

.h文件

#include <QDialog>
#include <QPainter>
#include <QPaintEvent>
#include <QMouseEvent>
#include <QPixmap>
#include <QPoint>
#include <QPointF>

函数声明
 protected:
    void paintEvent(QPaintEvent *);
    void mouseReleaseEvent(QMouseEvent *);
    void mousePressEvent(QMouseEvent *);
    void mouseMoveEvent(QMouseEvent *);

私有变量
private:
Ui::Dialog *ui;
QPixmap pix;
QPoint lastPoint;
QPoint endPoint;

.cpp文件

构造函数

    Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);

    resize(600,500);
    pix=QPixmap(200,200);
    pix.fill(Qt::white);
}

函数定义

    //根据鼠标前后两个指针就能绘制直线
    void Dialog::paintEvent(QPaintEvent *){
    QPainter pp(&pix);
    pp.drawLine(lastPoint,endPoint);
    lastPoint=endPoint;
    QPainter painter(this);
    painter.drawPixmap(0,0,pix);
    }


    //鼠标按下获得开始点
    void Dialog::mousePressEvent(QMouseEvent *event){
        if(event->button()==Qt::LeftButton){//鼠标左键按下
            lastPoint=event->pos();
        }
    }

    //当鼠标移动时获得结束点，并更新绘制。
    //调用update()函数会执行paintEvent()函数进行重新绘制。
    void Dialog::mouseMoveEvent(QMouseEvent *event){
        if(event->buttons()&Qt::LeftButton)
        {
            endPoint=event->pos();
            update();//进行绘制
        }
    }


    //当鼠标释放时，也进行重新绘制
    void Dialog::mouseReleaseEvent(QMouseEvent *event){
        if(event->button()==Qt::LeftButton)
        {
            endPoint=event->pos();
            update();
        }
    }