qt 旋转矩形,鼠标拉伸矩形框变形了

在Qt中旋转矩形可以使用QTransform类。为了在旋转后保持矩形的形状，您需要使用`QPainter::setWorldTransform()`方法将变换应用于绘制操作。然后，您可以使用鼠标事件来实现拖拽和拉伸矩形的功能。

下面是一个示例代码，展示了如何旋转矩形并实现拖拽和拉伸矩形的功能：

#include <QtWidgets>

class MyWidget : public QWidget
{
public:
    MyWidget(QWidget *parent = nullptr)
        : QWidget(parent)
    {
        setMouseTracking(true);
        setFixedSize(400, 400);
        m_rect = QRect(100, 100, 100, 50);
        m_rotation = 0;
    }

protected:
    void paintEvent(QPaintEvent *) override
    {
        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing);

        painter.save();
        painter.translate(m_rect.center());
        painter.rotate(m_rotation);
        painter.drawRect(-m_rect.width() / 2, -m_rect.height() / 2, m_rect.width(), m_rect.height());
        painter.restore();
    }

    void mousePressEvent(QMouseEvent *event) override
    {
        if (event->button() == Qt::LeftButton)
        {
            m_dragStartPosition = event->pos();
            m_dragging = true;
        }
    }

    void mouseMoveEvent(QMouseEvent *event) override
    {
        if (m_dragging)
        {
            QPoint diff = event->pos() - m_dragStartPosition;
            m_rect.translate(diff);
            m_dragStartPosition = event->pos();
            update();
        }
        else
        {
            QRect top = QRect(m_rect.x() + m_rect.width() / 4, m_rect.y() - 2, m_rect.width() / 2, 4);
            QRect bottom = QRect(m_rect.x() + m_rect.width() / 4, m_rect.y() + m_rect.height() - 2, m_rect.width() / 2, 4);
            QRect left = QRect(m_rect.x() - 2, m_rect.y() + m_rect.height() / 4, 4, m_rect.height() / 2);
            QRect right = QRect(m_rect.x() + m_rect.width() - 2, m_rect.y() + m_rect.height() / 4, 4, m_rect.height() / 2);

            if (top.contains(event->pos()))
            {
                setCursor(Qt::SizeVerCursor);
            }
            else if (bottom.contains(event->pos()))
            {
                setCursor(Qt::SizeVerCursor);
            }
            else if (left.contains(event->pos()))
            {
                setCursor(Qt::SizeHorCursor);
            }
            else if (right.contains(event->pos()))
            {
                setCursor(Qt::SizeHorCursor);
            }
            else
            {
                setCursor(Qt::ArrowCursor);
            }
        }
    }

    void mouseReleaseEvent(QMouseEvent *event) override
    {
        Q_UNUSED(event);
        m_dragging = false;
    }

    void mouseDoubleClickEvent(QMouseEvent *event) override
    {
        Q_UNUSED(event);
        m_rotation += 20;
        update();
    }

    void resizeEvent(QResizeEvent *) override
    {
        m_rect.moveCenter(rect().center());
    }

private:
    QRect m_rect;
    int m_rotation;
    QPoint m_dragStartPosition;
    bool m_dragging;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MyWidget w;
    w.show();
    return a.exec();
}

此示例中，我们使用`QPainter::setWorldTransform()`方法将变换应用于绘制操作。我们还使用鼠标事件来实现拖拽和拉伸矩形的功能。在`mouseMoveEvent()`方法中，我们检查鼠标位置是否在矩形的边缘，并相应地更改光标形状。在`mouseDoubleClickEvent()`方法中，我们旋转矩形20度。