Qt绘图

#ifndef PAINTEDWIDGET_H
#define PAINTEDWIDGET_H

#include <QWidget>
#include <QPainter>

QT_BEGIN_NAMESPACE
namespace Ui { class PaintedWidget; }
QT_END_NAMESPACE

class PaintedWidget : public QWidget
{
    Q_OBJECT

public:
    PaintedWidget(QWidget *parent = nullptr);
    ~PaintedWidget();
protected:
    void paintEvent(QPaintEvent *);
    //added new codes
    //重写QWidget的paintEvent()函数

private:
    Ui::PaintedWidget *ui;
};
#endif // PAINTEDWIDGET_H

#include "paintedwidget.h"
#include "ui_paintedwidget.h"

PaintedWidget::PaintedWidget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::PaintedWidget)
{
    ui->setupUi(this);
    resize(800,600);
    setWindowTitle(tr("Pain Demo"));
}
void PaintedWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.drawLine(100,100,400,400);
    //draws a line from (100,100) to (400,400)
    painter.setPen(Qt::red);
    painter.drawRect(10,10,100,400);
    //绘制矩形图形
    painter.setPen(QPen(Qt::green,5));
    painter.setBrush(Qt::blue);
    painter.drawEllipse(50,50,400,200);
    //绘制椭圆图形
}

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