QGraphicsRectItem美观实现缩放，旋转，平移

在使用QGraphicsRectItem时，涉及到需要缩放控件，于是在网上查找相关代码。很幸运的很快就找到了一个python写的旋转方法，效果也正是我想要的，于是我将代码改为C++的，测试成功。后来增加旋转需求，很幸运，这部分代码同样支持旋转，即旋转后仍然可以进行缩放。至于界面效果，我大概完整地实现了同PS上操作矩形的方式。
python参考地址：http://www.chinaoc.com.cn/p/1177045.html

效果demo展示

接口文件及说明

实现思路

放缩部分：我只是对python原文进行了python到C++转译而已，思路参见http://www.chinaoc.com.cn/p/1177045.html。

旋转部分思路：在view的mouseMoveEvent中调用getRotateCursor，获取指针形状。针对item设置c_rotate_tolerance 旋转容忍度，只有接近item周围才会支持旋转。mousePressEvent中设置setRotateStart，表示鼠标已按下，开始旋转。同时为了实现动态旋转，在mouseMoveEvent重复调用setRotateEnd，设置鼠标实时位置。

注1：使用时，应将mapCursors中的地址换成正确有效的地址。
注2：由于上述的放缩是基于item内部坐标完成的放缩，所以旋转并不会影响其效果。所以，你大可以重新实现更好的旋转效果，如果可以的话，也可以分享给我你的想法。

#include <QGraphicsRectItem>
#include <QStyleOptionGraphicsItem>
#include <QStyleOption>
#include <QCursor>const Qt::CursorShape handleCursors[] = {Qt::SizeFDiagCursor,Qt::SizeVerCursor,Qt::SizeBDiagCursor,Qt::SizeHorCursor,Qt::SizeFDiagCursor,Qt::SizeVerCursor,Qt::SizeBDiagCursor,Qt::SizeHorCursor,
};const QString mapCursors[] = {"",":/QtGuiApplication4/Resources/rotate_top_left.png",":/QtGuiApplication4/Resources/rotate_top_middle.png",":/QtGuiApplication4/Resources/rotate_top_right.png",":/QtGuiApplication4/Resources/rotate_middle_right.png",":/QtGuiApplication4/Resources/rotate_bottom_right.png",":/QtGuiApplication4/Resources/rotate_bottom_middle.png",":/QtGuiApplication4/Resources/rotate_bottom_left.png",":/QtGuiApplication4/Resources/rotate_middle_left.png"
};class CustomRectItem : public QGraphicsRectItem
{enum MOUSEHANDLE {handleNone = 0,handleTopLeft = 1,handleTopMiddle = 2,handleTopRight = 3,handleMiddleRight = 4,handleBottomRight = 5,handleBottomMiddle = 6,handleBottomLeft = 7,handleMiddleLeft = 8,};enum MOUSEROTATEHANDLE {handleRotateNone = 0,handleRotateTopLeft = 1,handleRotateTopMiddle = 2,handleRotateTopRight = 3,handleRotateMiddleRight = 4,handleRotateBottomRight = 5,handleRotateBottomMiddle = 6,handleRotateBottomLeft = 7,handleRotateMiddleLeft = 8,};const float c_handle_size = 8.0;const float c_handle_space = -4.0;const float c_rotate_tolerance = 20.0;const int c_handle_cursors_size = 8;   // handleCursors[] sizeconst int c_rotate_cursors_size = 9;    // MOUSEROTATEHANDLE sizeconst QSize c_rotate_cursor_size = QSize(20, 20);public:CustomRectItem(QGraphicsItem *parent = Q_NULLPTR);~CustomRectItem();// Returns the shape of this item as a QPainterPath in local coordinates.QPainterPath shape() const override;// Returns the bounding rect of the shape (including the resize handles).QRectF boundingRect() const override;void updateHandlesPos();bool isHover();// point is scene coordinateQCursor getRotateCursor(const QPointF& point);// set point for start rorate// @note point is scene coordinatevoid setRotateStart(const QPointF& point);// set point for end rorate// @note point is scene coordinatevoid setRotateEnd(const QPointF& point);protected:void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) Q_DECL_OVERRIDE;void hoverEnterEvent(QGraphicsSceneHoverEvent *event);//  Executed when the mouse leaves the shape (NOT PRESSED).void hoverLeaveEvent(QGraphicsSceneHoverEvent *event);// Executed when the mouse moves over the shape (NOT PRESSED).void hoverMoveEvent(QGraphicsSceneHoverEvent *event);//  Executed when the mouse is being moved over the item while being pressed.void mouseMoveEvent(QGraphicsSceneMouseEvent *event);// Executed when the mouse is pressed on the item.void mousePressEvent(QGraphicsSceneMouseEvent *event);// Executed when the mouse is released from the item.void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);// Executed when the key is pressed on the item.void keyPressEvent(QKeyEvent *event);private://  Returns the resize handle below the given point.MOUSEHANDLE handleAt(const QPointF& point);//  Perform shape interactive resize.void interactiveResize(const QPointF& mousePos);// the length2 with point1 and point2float getLength2(const QPointF& point1, const QPointF& point2);private:std::map<MOUSEROTATEHANDLE, QPointF> m_points;std::map<MOUSEROTATEHANDLE, QCursor> m_cursorRotate;std::map<MOUSEHANDLE, QRectF> m_handles;MOUSEHANDLE m_handle;QCursor m_cursor;QPointF m_mousePressPos;QRectF m_mousePressRect;QPointF m_mouseRotateStart;float m_fLastAngle;MOUSEHANDLE m_bhandleSelected;bool m_isHover;
};

源文件代码参考

分步介绍我就不加头文件咯！另外，我是摘出来的这段代码，有小错误的话，自己纠正一下就行咯！

重载paint函数，绘制了选中时的，边角矩形和去掉了选中状态（那种难看的虚线框）。

void CustomRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{QStyleOptionGraphicsItem op;if (widget == nullptr)op = *option;elseop.initFrom(widget);if (option->state & QStyle::State_Selected)op.state = QStyle::State_None;QGraphicsRectItem::paint(painter, &op, widget);if (isSelected() == true){painter->setRenderHint(QPainter::Antialiasing);painter->setBrush(QBrush(QColor(255, 255, 255, 255)));painter->setPen(QPen(QColor(0x293a56ff), 1.0, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));for (auto it : m_handles){if (m_bhandleSelected == MOUSEHANDLE::handleNone || it.first == m_bhandleSelected)painter->drawRect(it.second);}}
}

初始化部分，不做介绍。

CustomRectItem::CustomRectItem(QGraphicsItem * parent): QGraphicsRectItem(parent), m_points(), m_cursorRotate(), m_handles(), m_handle(MOUSEHANDLE::handleNone), m_cursor(Qt::ArrowCursor), m_mousePressPos(), m_mousePressRect(), m_mouseRotateStart(), m_fLastAngle(0.0), m_bhandleSelected(MOUSEHANDLE::handleNone), m_isHover(false)
{setAcceptHoverEvents(true);setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsFocusable | QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemSendsGeometryChanges);m_handles.insert(std::make_pair(MOUSEHANDLE::handleTopLeft, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleTopMiddle, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleTopRight, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleMiddleLeft, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleMiddleRight, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleBottomLeft, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleBottomMiddle, QRectF()));m_handles.insert(std::make_pair(MOUSEHANDLE::handleBottomRight, QRectF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateTopLeft, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateTopMiddle, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateTopRight, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateMiddleRight, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateBottomRight, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateBottomMiddle, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateBottomLeft, QPointF()));m_points.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateMiddleLeft, QPointF()));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateTopLeft, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateTopLeft]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateTopMiddle, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateTopMiddle]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateTopRight, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateTopRight]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateMiddleRight, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateMiddleRight]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateBottomRight, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateBottomRight]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateBottomMiddle, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateBottomMiddle]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateBottomLeft, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateBottomLeft]).scaled(c_rotate_cursor_size))));m_cursorRotate.insert(std::make_pair(MOUSEROTATEHANDLE::handleRotateMiddleLeft, QCursor(QPixmap(mapCursors[MOUSEROTATEHANDLE::handleRotateMiddleLeft]).scaled(c_rotate_cursor_size))));updateHandlesPos();
}
CustomRectItem::~CustomRectItem()
{}

这部分我也不清楚什么意思。

QPainterPath CustomRectItem::shape() const
{QPainterPath path = QPainterPath();path.addRect(this->rect());if (this->isSelected()){for (auto shape : m_handles)path.addEllipse(shape.second);}return path;
}

调整了下有效边界，这影响着hoverEnterEvent，hoverLeaveEvent生效的范围。c_handle_size 是调整大小的方框的大小，c_handle_space表示方框嵌入item的宽度，是个负数，正常为c_handle_size 的一半。

QRectF CustomRectItem::boundingRect() const
{auto o = c_handle_size + c_handle_space;return this->rect().adjusted(-o, -o, o, o);
}

m_isHover 表示鼠标是否在item上。当进行放缩时，鼠标可能会出界，导致view捕捉到，并且修改指针形状，通过判断该参数可纠正。

void CustomRectItem::hoverEnterEvent(QGraphicsSceneHoverEvent * event)
{QGraphicsRectItem::hoverEnterEvent(event);m_isHover = true;
}
void CustomRectItem::hoverLeaveEvent(QGraphicsSceneHoverEvent * event)
{setCursor(Qt::ArrowCursor);QGraphicsRectItem::hoverLeaveEvent(event);m_isHover = false;
}

这里基于python的原文，进行了适当修改。当item进行了旋转后，鼠标指针的方向也应该跟着改变。而且这里有个22.5度的逆向偏移。如果不理解可以运行demo，去掉试试。比如，旋转角度为44度，46度时，会有一个看着别扭。

void CustomRectItem::hoverMoveEvent(QGraphicsSceneHoverEvent * event)
{if (isSelected()){m_handle = handleAt(event->pos());if (MOUSEHANDLE::handleNone == m_handle)m_cursor = Qt::SizeAllCursor;else{float angle = this->rotation() + 22.5;while (angle >= 360.0)angle -= 360;// choose the right cursorm_cursor = handleCursors[((int)m_handle + (int)(angle / 45) - 1) % c_handle_cursors_size];}setCursor(m_cursor);}   QGraphicsRectItem::hoverMoveEvent(event);
}

判断鼠标指针的状态，进行调整大小。

void CustomRectItem::mouseMoveEvent(QGraphicsSceneMouseEvent * event)
{if (MOUSEHANDLE::handleNone != m_bhandleSelected)interactiveResize(event->pos());elseQGraphicsRectItem::mouseMoveEvent(event);
}void CustomRectItem::mousePressEvent(QGraphicsSceneMouseEvent * event)
{m_bhandleSelected = handleAt(event->pos());if (MOUSEHANDLE::handleNone != m_bhandleSelected){m_mousePressPos = event->pos();m_mousePressRect = boundingRect();}QGraphicsRectItem::mousePressEvent(event);
}

<这里前半部分是个重点>
目的是解决有旋转角度的矩形，拉伸之后，再次旋转，旋转中心该仍然为之前坐标，手动设置为中心，会产生漂移的问题。如果不需要解决该问题，可注掉该部分代码。原理参见子章节：https://blog.csdn.net/xiaonuo911teamo/article/details/106129696

void CustomRectItem::mouseReleaseEvent(QGraphicsSceneMouseEvent * event)
{auto rr = this->rect();auto angle = qDegreesToRadians(this->rotation());auto p1 = rr.center();auto origin = this->transformOriginPoint();QPointF p2 = QPointF(0, 0);p2.setX(origin.x() + qCos(angle)*(p1.x() - origin.x()) - qSin(angle)*(p1.y() - origin.y()));p2.setY(origin.y() + qSin(angle)*(p1.x() - origin.x()) + qCos(angle)*(p1.y() - origin.y()));auto diff = p1 - p2;this->setRect(rr.adjusted(-diff.x(), -diff.y(), -diff.x(), -diff.y()));setTransformOriginPoint(this->rect().center());updateHandlesPos();m_bhandleSelected = MOUSEHANDLE::handleNone;m_mousePressPos = QPointF();m_mousePressRect = QRectF();this->update();QGraphicsRectItem::mouseReleaseEvent(event);
}

键盘控制平移的简单实现。

void CustomRectItem::keyPressEvent(QKeyEvent * event)
{switch (event->key()){case Qt::Key_Up:this->moveBy(0, -1);event->setAccepted(true);break;case Qt::Key_Down:this->moveBy(0, 1);event->setAccepted(true);break;case Qt::Key_Left:this->moveBy(-1, 0);event->setAccepted(true);break;case Qt::Key_Right:this->moveBy(1, 0);event->setAccepted(true);break;default:event->setAccepted(false);break;}//QGraphicsRectItem::keyPressEvent(event);
}

调整四周小矩形的位置和大小。

void CustomRectItem::updateHandlesPos()
{auto s = c_handle_size;auto b = boundingRect();m_handles[MOUSEHANDLE::handleTopLeft] = QRectF(b.left(), b.top(), s, s);m_handles[MOUSEHANDLE::handleTopMiddle] = QRectF(b.center().x() - s / 2, b.top(), s, s);m_handles[MOUSEHANDLE::handleTopRight] = QRectF(b.right() - s, b.top(), s, s);m_handles[MOUSEHANDLE::handleMiddleLeft] = QRectF(b.left(), b.center().y() - s / 2, s, s);m_handles[MOUSEHANDLE::handleMiddleRight] = QRectF(b.right() - s, b.center().y() - s / 2, s, s);m_handles[MOUSEHANDLE::handleBottomLeft] = QRectF(b.left(), b.bottom() - s, s, s);m_handles[MOUSEHANDLE::handleBottomMiddle] = QRectF(b.center().x() - s / 2, b.bottom() - s, s, s);m_handles[MOUSEHANDLE::handleBottomRight] = QRectF(b.right() - s, b.bottom() - s, s, s);
}bool CustomRectItem::isHover()
{return m_isHover;
}

判断是否在可旋转范围内，是则返回对应的QCursor。计算应当返回什么QCursor的思路是，先在item坐标下，计算出距离最近的是哪个小方块，然后再加上旋转角度的偏移量，就得到了应该在视觉上看到的正确的鼠标形状。或许有更方便的实现方法。

QCursor CustomRectItem::getRotateCursor(const QPointF & point)
{if (m_isHover == true || !isSelected())return QCursor();if (boundingRect().contains(mapFromScene(point)))return QCursor();auto srcRect = rect();auto frameRect = srcRect.adjusted(-c_rotate_tolerance, -c_rotate_tolerance, c_rotate_tolerance, c_rotate_tolerance);QPointF innerPoint = mapFromScene(point);if (!frameRect.contains(innerPoint))return QCursor();m_points[MOUSEROTATEHANDLE::handleRotateTopLeft] = srcRect.topLeft();m_points[MOUSEROTATEHANDLE::handleRotateTopMiddle] = QPointF(srcRect.center().x(), srcRect.top());m_points[MOUSEROTATEHANDLE::handleRotateTopRight] = srcRect.topRight();m_points[MOUSEROTATEHANDLE::handleRotateMiddleRight] = QPointF(srcRect.right(), srcRect.center().y());m_points[MOUSEROTATEHANDLE::handleRotateBottomRight] = srcRect.bottomRight();m_points[MOUSEROTATEHANDLE::handleRotateBottomMiddle] = QPointF(srcRect.center().x(), srcRect.bottom());m_points[MOUSEROTATEHANDLE::handleRotateBottomLeft] = srcRect.bottomLeft();m_points[MOUSEROTATEHANDLE::handleRotateMiddleLeft] = QPointF(srcRect.left(), srcRect.center().y());auto ret = MOUSEROTATEHANDLE::handleRotateNone;float l = 3.4028235E38;for (auto& iter : m_points){auto length = getLength2(iter.second, innerPoint);if (length < l){l = length;ret = iter.first;}}if (ret == MOUSEROTATEHANDLE::handleRotateNone)return QCursor();float angle = this->rotation() + 22.5;while (angle >= 360.0)angle -= 360;ret = MOUSEROTATEHANDLE(((int)ret + (int)( angle/ 45)) % c_rotate_cursors_size);if (ret == MOUSEROTATEHANDLE::handleRotateNone)ret = MOUSEROTATEHANDLE::handleRotateTopLeft;return m_cursorRotate[ret];
}

设置setRotateStart，表示开始旋转，记录此时的鼠标落点和角度。
设置setRotateEnd，基于上次设置的Start，进行旋转。并且始终保持rotation在[0,360)之间。
注：point是场景坐标。

void CustomRectItem::setRotateStart(const QPointF & point)
{m_mouseRotateStart = point;m_fLastAngle = rotation();
}
void CustomRectItem::setRotateEnd(const QPointF & point)
{QPointF ori = mapToScene(transformOriginPoint());QPointF v1 = m_mouseRotateStart - ori;QPointF v2 = point - ori;float angle = std::atan2f(v2.y(), v2.x()) - std::atan2f(v1.y(), v1.x());angle = m_fLastAngle + angle * 180 / 3.1415926;// angle = [0,360)while (angle < 0.0)angle += 360;while (angle >= 360.0)angle -= 360;setRotation(angle);
}

判断鼠标位置，应为的鼠标状态。

CustomRectItem::MOUSEHANDLE CustomRectItem::handleAt(const QPointF& point)
{for (auto it : m_handles){if (it.second.contains(point))return it.first;}return MOUSEHANDLE::handleNone;
}

调整大小

void CustomRectItem::interactiveResize(const QPointF & mousePos)
{auto offset = c_handle_size + c_handle_space;auto bRect = boundingRect();auto rr = this->rect();auto diff = QPointF(0, 0);prepareGeometryChange();if (m_bhandleSelected == MOUSEHANDLE::handleTopLeft){auto fromX = m_mousePressRect.left();auto fromY = m_mousePressRect.top();auto toX = fromX + mousePos.x() - m_mousePressRect.x();auto toY = fromY + mousePos.y() - m_mousePressRect.y();if (!(toX - fromX >= rr.width() || toY - fromY >= rr.height())){diff.setX(toX - fromX);diff.setY(toY - fromY);bRect.setLeft(toX);bRect.setTop(toY);rr.setLeft(bRect.left() + offset);rr.setTop(bRect.top() + offset);this->setRect(rr);}        }else if (m_bhandleSelected == MOUSEHANDLE::handleTopMiddle){auto fromY = m_mousePressRect.top();auto toY = fromY + mousePos.y() - m_mousePressPos.y();if (!(toY - fromY >= rr.height())){diff.setY(toY - fromY);bRect.setTop(toY);rr.setTop(bRect.top() + offset);this->setRect(rr);} }else if (m_bhandleSelected == MOUSEHANDLE::handleTopRight){auto fromX = m_mousePressRect.right();auto fromY = m_mousePressRect.top();auto toX = fromX + mousePos.x() - m_mousePressPos.x();auto toY = fromY + mousePos.y() - m_mousePressPos.y();if (!(fromX - toX >= rr.width() || toY - fromY >= rr.height())){diff.setX(toX - fromX);diff.setY(toY - fromY);bRect.setRight(toX);bRect.setTop(toY);rr.setRight(bRect.right() - offset);rr.setTop(bRect.top() + offset);this->setRect(rr);}}else if (m_bhandleSelected == MOUSEHANDLE::handleMiddleLeft){auto fromX = m_mousePressRect.left();auto toX = fromX + mousePos.x() - m_mousePressPos.x();if (!(toX - fromX >= rr.width())){diff.setX(toX - fromX);bRect.setLeft(toX);rr.setLeft(bRect.left() + offset);this->setRect(rr);}        }else if (m_bhandleSelected == MOUSEHANDLE::handleMiddleRight){auto fromX = m_mousePressRect.right();auto toX = fromX + mousePos.x() - m_mousePressPos.x();if (!(fromX - toX >= rr.width())){diff.setX(toX - fromX);bRect.setRight(toX);rr.setRight(bRect.right() - offset);this->setRect(rr);}}else if (m_bhandleSelected == MOUSEHANDLE::handleBottomLeft){auto fromX = m_mousePressRect.left();auto fromY = m_mousePressRect.bottom();auto toX = fromX + mousePos.x() - m_mousePressPos.x();auto toY = fromY + mousePos.y() - m_mousePressPos.y();if (!(toX - fromX >= rr.width() || fromY - toY >= rr.height())){diff.setX(toX - fromX);diff.setY(toY - fromY);bRect.setLeft(toX);bRect.setBottom(toY);rr.setLeft(bRect.left() + offset);rr.setBottom(bRect.bottom() - offset);this->setRect(rr);}  }else if (m_bhandleSelected == MOUSEHANDLE::handleBottomMiddle){auto fromY = m_mousePressRect.bottom();auto toY = fromY + mousePos.y() - m_mousePressPos.y();if (!(fromY - toY >= rr.height())){diff.setY(toY - fromY);bRect.setBottom(toY);rr.setBottom(bRect.bottom() - offset);this->setRect(rr);}}else if (m_bhandleSelected == MOUSEHANDLE::handleBottomRight){auto fromX = m_mousePressRect.right();auto fromY = m_mousePressRect.bottom();auto toX = fromX + mousePos.x() - m_mousePressPos.x();auto toY = fromY + mousePos.y() - m_mousePressPos.y();if (!(fromX - toX >= rr.width() || fromY - toY >= rr.height())){diff.setX(toX - fromX);diff.setY(toY - fromY);bRect.setRight(toX);bRect.setBottom(toY);rr.setRight(bRect.right() - offset);rr.setBottom(bRect.bottom() - offset);this->setRect(rr);}}updateHandlesPos();
}

简单的求两点距离平方的函数。因为这不属于这个类的附属功能，所以没有开放。当然，声明为static private会更好。

float CustomRectItem::getLength2(const QPointF & point1, const QPointF & point2)
{return (point1.x() - point2.x()) * (point1.x() - point2.x()) + (point1.y() - point2.y()) * (point1.y() - point2.y());
}

使用实例

#pragma once#include <QtWidgets/QWidget>
#include <QGraphicsView>
#include "CustomRectItem.h"
#include "ui_QtGuiApplication4.h"class QtGuiApplication4 : public QGraphicsView
{Q_OBJECTpublic:QtGuiApplication4(QWidget *parent = Q_NULLPTR);void mouseMoveEvent(QMouseEvent* event) override;void mousePressEvent(QMouseEvent* event) override;void mouseReleaseEvent(QMouseEvent* event) override;private:// the length2 with point1 and point2float getLength2(const QPointF& point1, const QPointF& point2);private:Ui::QtGuiApplication4Class ui;QGraphicsScene* m_scene;CustomRectItem* m_rect;volatile bool m_bTurn;
};

#include "QtGuiApplication4.h"
#include <QDebug>
#include <QMouseEvent>
#include <QTimer>
#include <QBitmap>QtGuiApplication4::QtGuiApplication4(QWidget *parent): QGraphicsView(parent), m_rect(nullptr), m_scene(nullptr), m_bTurn(false)
{ui.setupUi(this);m_scene = new QGraphicsScene();setScene(m_scene);resize(400, 400);QTimer::singleShot(1000, [this]() {m_rect = new CustomRectItem();m_rect->setPos(50, 50);m_scene->addItem(m_rect);m_rect->setRect(0, 0, 50, 50);m_rect->setTransformOriginPoint(25, 25);m_rect->setRotation(45);});
}void QtGuiApplication4::mouseMoveEvent(QMouseEvent * event)
{if (m_bTurn != true){QCursor cursor = m_rect->getRotateCursor(mapToScene(event->pos()));if (!cursor.pixmap().isNull()){viewport()->setCursor(cursor);}else if (!m_rect->isHover()){viewport()->setCursor(Qt::ArrowCursor);}}else{m_rect->setRotateEnd(mapToScene(event->pos()));}QGraphicsView::mouseMoveEvent(event);
}void QtGuiApplication4::mousePressEvent(QMouseEvent * event)
{if (!m_rect->getRotateCursor(mapToScene(event->pos())).pixmap().isNull()){m_rect->setRotateStart(mapToScene(event->pos()));m_bTurn = true;}QGraphicsView::mousePressEvent(event);
}void QtGuiApplication4::mouseReleaseEvent(QMouseEvent * event)
{if (true == m_bTurn){m_bTurn = false;}QGraphicsView::mouseReleaseEvent(event);
}float QtGuiApplication4::getLength2(const QPointF & point1, const QPointF & point2)
{return (point1.x() - point2.x()) * (point1.x() - point2.x()) + (point1.y() - point2.y()) * (point1.y() - point2.y());
}