#include ...
#include ...

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}


//顯示影象，事件觸發
void MainWindow::paintEvent(QPaintEvent *)
{
    //QPainter painter(this);
    QPainter painter;

    int labelWid=ui->shapeLabel->width();
    int labelHei=ui->shapeLabel->height();

    QPixmap pix(labelWid,labelHei);//定義一個新的物件，並用給定的引數構建影象
    pix.fill(Qt::transparent);//透明

    painter.begin(&pix); //在pix上繪圖, 附帶重置屬性
    QPen pen1(Qt::red,5,Qt::DashLine,Qt::FlatCap,Qt::RoundJoin);
    painter.setPen(pen1);
    painter.drawLine(45,10,100,80);//直線
    QPen pen2(Qt::green,5,Qt::DashLine,Qt::FlatCap,Qt::RoundJoin);
    painter.setPen(pen2);
    painter.drawLine(75,10,100,60);
    painter.end();
    
    ui->shapeLabel->setPixmap(pix);//使用QLabel顯示pix上的繪製的影象

}