Qt绘图事件paintEvent

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QPainter>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

    void paintEvent(QPaintEvent *event) override
    {
        /* 实例化画家对象 this指定的是绘图设备 */
        QPainter painter(this);

        /* 设置画笔 */
        QPen pen(QColor(255, 0, 0));
        pen.setWidth(2);
        pen.setStyle(Qt::DotLine); //设置画笔风格
        painter.setPen(pen); //让画家使用这个笔

        /* 设置画刷 */
        QBrush brush(Qt::green);
        brush.setStyle(Qt::Dense2Pattern); //设置画刷风格
        painter.setBrush(brush); //让画家使用画刷

        /* 画线 */
        painter.drawLine(QPoint(0, 0), QPoint(100, 100));
        /* 画圆 */
        painter.drawEllipse(QPoint(100, 100), 50, 50);
        /* 画矩形 */
        painter.drawRect(QRect(150, 150, 50, 50));
        /* 画文字 */
        painter.drawText(QPoint(0, 250), "hello furong");
    }

private:
    Ui::Widget *ui;
};
#endif // WIDGET_H