Qt二维绘图基础之setView和setWindow

Qt绘图之setView

该设置是针对绘图设备的坐标，假设定义paintEvent如下所示

void Widget::paintEvent(QPaintEvent *)
{
    QPainter  paint(this);
    paint.setRenderHint(QPainter::Antialiasing);   //设置绘图返走样
    paint.setRenderHint(QPainter::TextAntialiasing);//设置字体反走样
    int side = qMin(this->width(),this->height());
    paint.setPen(QColor("#521258"));
    paint.drawLine(QLineF(QPointF(0,0),QPointF(width(),height())));
    paint.drawLine(QLineF(QPointF(0,height()),QPointF(width(),0)));
}

编译之后输出如下所示
此时绘制的图像符合我们的预期，下边开始设置setView

void Widget::paintEvent(QPaintEvent *)
{
    QPainter  paint(this);
    paint.setRenderHint(QPainter::Antialiasing);        //设置绘图返走样
    paint.setRenderHint(QPainter::TextAntialiasing);    //设置字体反走样
    paint.setViewport(width()/2,height()/2,200,200);
    int side = qMin(this->width(),this->height());
    paint.setPen(QColor("#521258"));
    paint.drawLine(QLineF(QPointF(0,0),QPointF(width(),height())));
    paint.drawLine(QLineF(QPointF(0,height()),QPointF(width(),0)));
    paint.setPen(QColor("#A02565"));
    }

可以这样理解，setView是重定向绘图，但同时View设置的大小也会影响绘图整体的大小

下边开始同时设置setWindow和setView

QPainter  paint(this);
    paint.setRenderHint(QPainter::Antialiasing);        //设置绘图返走样
    paint.setRenderHint(QPainter::TextAntialiasing);    //设置字体反走样
    int side = qMin(this->width(),this->height());
    paint.setPen(QColor("#521258"));
    paint.drawLine(QLineF(QPointF(0,0),QPointF(width(),height())));
    paint.drawLine(QLineF(QPointF(0,height()),QPointF(width(),0)));
    paint.setPen(QColor("#A02565"));
    paint.setViewport(width()/2,height()/2,200,200);
    paint.setWindow(0,0,side,side);
    for(int i = 0; i < 400; i++)
    {
        paint.drawEllipse(QPointF(0,i),80,80);
        qDebug()<<"Start to paint and rotate~"<<endl;
        paint.rotate(18);
    }

显示如图所示，
可以看到在窗体的中间画了一幅图，但是当我们窗口放置最大化时，绘制的图形也是在View之内，但是坐标执行的是window的坐标，且View的左上角是window的坐标原点，绘制是基于Window来绘制的。

初始情况下，默认view和window是重合的，是窗口的左上角顶点。
如有问题，可留言提问，该文章针对想要学习自绘控件的初学者，高手越过，如有错误，请指正。