Qt实用技巧：组合图形的比例变换

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需求

        对三个组合矩形进行比例变化，Demo实现效果如下：

原理解说图

关键代码

void MainWindow::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.save();
    painter.setPen(Qt::black);
    int rectx = _rectx + _dx;
    int recty = _recty + _dy;
    int rectWidth = _rectWidth/(float)_width*(_width+_dwidth);
    int rectHeight = _rectHeight/(float)_height*(_height+_dheight);
    painter.drawRect(rectx, recty, rectWidth, rectHeight);
    painter.restore();

    painter.save();
    painter.setPen(Qt::red);
    int rect2x = _rectx + _dx + (_rect2x-_rectx)/(float)_rectWidth*rectWidth;
    int rect2y = _recty + _dy + (_rect2y-_recty)/(float)_rectHeight*rectHeight;
    int rect2Width = _rect2Width/(float)_rectWidth*rectWidth;
    int rect2Height = _rect2Height/(float)_rectHeight*rectHeight;
    painter.drawRect(rect2x, rect2y, rect2Width, rect2Height);
    painter.restore();

    painter.save();
    painter.setPen(Qt::blue);
    int rect3x = _rectx + _dx + (_rect3x-_rectx)/(float)_rectWidth*rectWidth;
    int rect3y = _recty + _dy + (_rect3y-_recty)/(float)_rectHeight*rectHeight;
    int rect3Width = _rect3Width/(float)_rectWidth*rectWidth;
    int rect3Height = _rect3Height/(float)_rectHeight*rectHeight;
    painter.drawRect(rect3x, rect3y, rect3Width, rect3Height);
    painter.restore();
}