qt旋转矩形后,鼠标拖动改变矩形依旧不变 具体例子

下面是一个基于Qt的例子，展示如何实现旋转矩形后，鼠标拖动改变矩形但依旧保持不变的效果。您可以根据自己的需求进行修改：

#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QApplication>
#include <QMouseEvent>
#include <QPointF>
#include <cmath>

class RotatableRect : public QGraphicsRectItem
{
public:
    RotatableRect(qreal x, qreal y, qreal w, qreal h): QGraphicsRectItem(x, y, w, h)
    {
        setFlag(QGraphicsItem::ItemIsMovable);
        setFlag(QGraphicsItem::ItemSendsGeometryChanges);
        setFlag(QGraphicsItem::ItemIsSelectable);

        angle = 0.0;
        center = rect().center();
    }

    enum { Type = UserType + 1 };
    int type() const override { return Type; }

    void mousePressEvent(QGraphicsSceneMouseEvent *event) override
    {
        if (event->button() == Qt::LeftButton)
        {
            prev_mouse_pos = event->scenePos();
            prev_pos = pos();
        }
        QGraphicsRectItem::mousePressEvent(event);
    }

    void mouseMoveEvent(QGraphicsSceneMouseEvent *event) override
    {
        if (event->buttons() & Qt::LeftButton)
        {
            QPointF mouse_diff = event->scenePos() - prev_mouse_pos;
            QPointF new_pos = prev_pos + mouse_diff;

            // calculate new coordinates in rotated system
            QPointF delta = new_pos - pos();
            qreal dx = delta.x();
            qreal dy = delta.y();
            qreal cos_a = std::cos(-angle);
            qreal sin_a = std::sin(-angle);
            qreal x = cos_a * dx - sin_a * dy;
            qreal y = sin_a * dx + cos_a * dy;
            QPointF new_pos_rotated = pos() + QPointF(x, y);

            // update item position
            setPos(new_pos_rotated - center);
        }
        QGraphicsRectItem::mouseMoveEvent(event);
    }

    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override
    {
        QGraphicsRectItem::mouseReleaseEvent(event);
    }

    QRectF boundingRect() const override
    {
        QRectF rect = QGraphicsRectItem::boundingRect();
        qreal margin = 2.0;
        return rect.adjusted(-margin, -margin, margin, margin);
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override
    {
        painter->save();
        painter->translate(center);
        painter->rotate(angle);
        painter->translate(-center);
        QGraphicsRectItem::paint(painter, option, widget);
        painter->restore();
    }

    QVariant itemChange(GraphicsItemChange change, const QVariant &value) override
    {
        if (change == QGraphicsItem::ItemPositionChange)
        {
            QPointF new_pos = value.toPointF();

            // calculate new coordinates in rotated system
            QPointF delta = new_pos - pos();
            qreal dx = delta.x();
            qreal dy = delta.y();
            qreal cos_a = std::cos(angle);
            qreal sin_a = std::sin(angle);
            qreal x = cos_a * dx - sin_a * dy;
            qreal y = sin_a * dx + cos_a * dy;
            QPointF new_pos_rotated = pos() + QPointF(x, y);

            // update item position
            return new_pos_rotated - center;
        }
        else if (change == QGraphicsItem::ItemTransformChange)
        {
            angle = transform().rotateRadians(0.0, Qt::ZAxis);
            center = rect().center();
        }
        return QGraphicsRectItem::itemChange(change, value);
    }

private:
    QPointF prev_mouse_pos;
    QPointF prev_pos;
    qreal angle;
    QPointF center;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QGraphicsScene scene;
    QGraphicsView view(&scene);
    view.setRenderHint(QPainter::Antialiasing);
    view.setDragMode(QGraphicsView::RubberBandDrag);

    RotatableRect *rect = new RotatableRect(-50, -50, 100, 100);
    rect->setBrush(Qt::red);
    scene.addItem(rect);

    view.setSceneRect(-200, -200, 400, 400);
    view.show();

    return a.exec();
}

在这个例子中，我们继承了QGraphicsRectItem类，重载了鼠标事件和位置变化事件，并且在paint()函数中实现了旋转矩形的绘制。在鼠标事件中，我们使用了旋转矩形的中心点和角度，将鼠标移动的距离转化为相对于旋转后的坐标系的坐标偏移量，并根据新的坐标计算出旋转后的矩形位置和大小。

最后，我们创建了一个RotatableRect对象，并将其添加到QGraphicsScene中。通过QGraphicsView来显示场景，您可以通过鼠标进行拖动并改变矩形的大小和位置，而矩形旋转后，鼠标拖动改变矩形但依旧不变。