Qt-Paint系统

Qt里面，要想画图，只有把画图的过程放入paintEvent()方法中，每次窗口变化时会回调paintEvent() 方法

Paint events are sent to widgets that need to update themselves, for
instance when part of a widget is exposed because a covering widget was
moved.

QPainter

The QPainter class performs low-level painting on widgets and other paint devices.

QPainter 类对象作用于继承QPaintDevice 类的对象

QPaintDevice

QPainter对象可以在QPaintDevice上进行绘画操作

常用的QPaintDevice 子类有QWidget, QPixmap, QImage

示例

//画图并保存为图片
void SomeWidget::painterEvent()
{
    QImage image(50,