Qt 通过重写QGraphicItem实现绘制、拖动、缩放、旋转矩形

本例程通过重写了一个类，继承自QGraphicItem，来实现了在qgraphicsScene上绘制、拖动、缩放、旋转矩形。
效果如下：
在这里插入图片描述

其实要实现绘制、拖动、缩放矩形都不难，难的是在旋转之后还要支持缩放。
我的思路是：
1.实现绘制矩形：只要定义一个全局变量QRectF m_oldRect，在外面矩形大小传进来，然后在paint函数里面绘制这个矩形就行
2.实现拖动矩形：重写mousePressEvent，mouseMoveEvent，mouseReleaseEvent，记录鼠标按下的起始点和移动时候的点，并用moveBy()函数来移动矩形即可
3.实现缩放：在矩形内部靠近4条边的地方定义4个矩形，当鼠标按下的时候在这4个矩形方框内，则将矩形往4个方向拉伸
4.实现旋转：
我给之前定义的矩形全部配一个QPolygonF，因为我只能通过绘制多边形的方式来画出旋转之后的矩形。
矩形正上方的圆圈我是通过三角函数+直线方程来计算，让其始终绘制在矩形左右两个顶点的中垂线上方。
当鼠标落在圆形内部的时候可以控制矩形旋转。
在矩形旋转之后，再进行拉伸的时候，我是通过的计算鼠标的点离对面的边的距离来重新计算矩形的大小，然后计算对应的QPolygonF的大小。

主要代码如下：
mygraphicrectitem.h

 1 #ifndef MYGRAPHICRECTITEM_H
 2 #define MYGRAPHICRECTITEM_H
 3 #include <QObject>
 4 #include <QWidget>
 5 #include <QMouseEvent>
 6 #include <QGraphicsScene>
 7 #include <QGraphicsRectItem>
 8 #include <QGraphicsSceneMouseEvent>
 9 #include <QRect>
10 #include <QPainter>
11 #include <QPolygon>
12 #include <QList>
13 enum STATE_FLAG{
14     DEFAULT_FLAG=0,
15     MOV_LEFT_LINE,//标记当前为用户按下矩形的左边界区域
16     MOV_TOP_LINE,//标记当前为用户按下矩形的上边界区域
17     MOV_RIGHT_LINE,//标记当前为用户按下矩形的右边界区域
18     MOV_BOTTOM_LINE,//标记当前为用户按下矩形的下边界区域
19     MOV_RIGHTBOTTOM_RECT,//标记当前为用户按下矩形的右下角
20     MOV_RECT,//标记当前为鼠标拖动图片移动状态
21     ROTATE//标记当前为旋转状态
22 };
23 class myGraphicRectItem:public QObject,public QGraphicsItem
24 {
25     Q_OBJECT
26 public:
27     myGraphicRectItem(QGraphicsItem *parent = nullptr);
28     //myGraphicRectItem(QRectF m_OriginRect = QRectF(0,0,100,100));
29     QRectF  boundingRect() const;
30     ~myGraphicRectItem();
31     void setRectSize(QRectF mrect,bool bResetRotateCenter = true);
32     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
33     void mousePressEvent(QGraphicsSceneMouseEvent *event);
34     void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
35     void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
36     void SetRotate(qreal RotateAngle,QPointF ptCenter=QPointF(-999,-999));
37     QPointF getRotatePoint(QPointF ptCenter, QPointF ptIn, qreal angle);//获取旋转后的点
38     QList<QPointF> getRotatePoints(QPointF ptCenter,QList<QPointF> ptIns,qreal angle);//获取多个旋转后的点
39     QPolygonF getRotatePolygonFromRect(QPointF ptCenter,QRectF rectIn,qreal angle);//将矩形旋转之后返回多边形
40     QRectF getCrtPosRectToSceen();
41     QRectF m_SmallRotateRect;//矩形顶部用来表示旋转的标记的矩形
42     QPolygonF m_SmallRotatePolygon;//矩形顶部用来表示旋转的标记的矩形旋转后形成的多边形
43     QPointF getSmallRotateRectCenter(QPointF ptA,QPointF ptB);//获取旋转时候矩形正上方的旋转标记矩形
44     QRectF  getSmallRotateRect(QPointF ptA,QPointF ptB);
45     bool    m_bRotate;
46     qreal   m_RotateAngle;
47     QPointF m_RotateCenter;
48 
49 private:
50     QRectF  m_oldRect;
51     QPolygonF m_oldRectPolygon;
52     QRectF  m_RotateAreaRect;
53     bool    m_bResize;
54     QPolygonF m_insicedPolygon;
55     QRectF  m_insicedRectf;
56     QPolygonF m_leftPolygon;
57     QRectF  m_leftRectf;
58     QPolygonF m_topPolygon;
59     QRectF  m_topRectf;
60     QPolygonF m_rightPolygon;
61     QRectF  m_rightRectf;
62     QPolygonF m_bottomPolygon;
63     QRectF  m_bottomRectf;
64 //    QPolygonF m_rbPolygon;
65 //    QRectF  m_rbRectf;
66     QPointF m_startPos;
67     STATE_FLAG m_StateFlag;
68     QPointF *pPointFofSmallRotateRect;
69 protected:
70 
71 };
72 #endif // MYGRAPHICRECTITEM_H

mygraphicrectitem.cpp

  1 #include "mygraphicrectitem.h"
  2 #include <QtMath>
  3 #include <QDebug>
  4 
  5 myGraphicRectItem::myGraphicRectItem(QGraphicsItem *parent):
  6     m_bResize(false),
  7     m_oldRect(0,0,100,100),
  8     m_bRotate(false),
  9     m_RotateAngle(0),
 10     m_StateFlag(DEFAULT_FLAG)
 11 {
 12     //setParent(parent);
 13     setRectSize(m_oldRect);
 14     setToolTip("Click and drag me!");  //提示
 15     setCursor(Qt::ArrowCursor);   //改变光标形状,手的形状
 16     setFlag(QGraphicsItem::ItemIsMovable);
 17     //    setAcceptDrops(true);
 18     pPointFofSmallRotateRect = new QPointF[4];
 19     SetRotate(0);
 20     setFlag(QGraphicsItem::ItemIsSelectable);//
 21 }
 22 
 23 QRectF myGraphicRectItem::boundingRect() const
 24 {
 25     //return m_oldRectPolygon.boundingRect();
 26     QRectF boundingRectF = m_oldRectPolygon.boundingRect();
 27     return QRectF(boundingRectF.x()-40,boundingRectF.y()-40,boundingRectF.width()+80,boundingRectF.height()+80);
 28 }
 29 
 30 myGraphicRectItem::~myGraphicRectItem()
 31 {
 32     delete []pPointFofSmallRotateRect;
 33     pPointFofSmallRotateRect = nullptr;
 34 }
 35 
 36 void myGraphicRectItem::setRectSize(QRectF mrect, bool bResetRotateCenter)
 37 {
 38     m_oldRect = mrect;
 39     if(bResetRotateCenter)
 40     {
 41         m_RotateCenter.setX(m_oldRect.x()+m_oldRect.width()/2);
 42         m_RotateCenter.setY(m_oldRect.y()+m_oldRect.height()/2);
 43     }
 44     m_oldRectPolygon = getRotatePolygonFromRect(m_RotateCenter,m_oldRect,m_RotateAngle);
 45 
 46     m_insicedRectf = QRectF(m_oldRect.x()+8,m_oldRect.y()+8,m_oldRect.width()-16,m_oldRect.height()-16);
 47     m_insicedPolygon =getRotatePolygonFromRect(m_RotateCenter,m_insicedRectf,m_RotateAngle);
 48 
 49     m_leftRectf = QRectF(m_oldRect.x(),m_oldRect.y(),8,m_oldRect.height()-8);
 50     m_leftPolygon = getRotatePolygonFromRect(m_RotateCenter,m_leftRectf,m_RotateAngle);
 51 
 52     m_topRectf = QRectF(m_oldRect.x()+8,m_oldRect.y(),m_oldRect.width()-8,8);
 53     m_topPolygon = getRotatePolygonFromRect(m_RotateCenter,m_topRectf,m_RotateAngle);
 54 
 55     m_rightRectf = QRectF(m_oldRect.right()-8,m_oldRect.y()+8,8,m_oldRect.height()-16);
 56     m_rightPolygon = getRotatePolygonFromRect(m_RotateCenter,m_rightRectf,m_RotateAngle);
 57 
 58     m_bottomRectf = QRectF(m_oldRect.x(),m_oldRect.bottom()-8,m_oldRect.width()-8,8);
 59     m_bottomPolygon = getRotatePolygonFromRect(m_RotateCenter,m_bottomRectf,m_RotateAngle);
 60 
 61 //    m_rbRectf = QRectF(m_oldRect.right()-8,m_oldRect.bottom()-8,8,8);
 62 //    m_rbPolygon = getRotatePolygonFromRect(m_RotateCenter,m_rbRectf,m_RotateAngle);
 63 
 64     m_SmallRotateRect = getSmallRotateRect(mrect.topLeft(),mrect.topRight());//矩形正上方的旋转标记矩形
 65     m_SmallRotatePolygon = getRotatePolygonFromRect(m_RotateCenter,m_SmallRotateRect,m_RotateAngle);
 66 }
 67 
 68 void myGraphicRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 69 {
 70     QPen mPen = QPen(Qt::yellow);
 71     painter->setPen(mPen);
 72     //绘制旋转后的矩形
 73     painter->drawPolygon(m_oldRectPolygon);
 74     //绘制旋转圆形
 75     mPen.setWidth(2);
 76     mPen.setColor(Qt::green);
 77     painter->setPen(mPen);
 78     QPointF pf = getSmallRotateRectCenter(m_oldRectPolygon[0],m_oldRectPolygon[1]);
 79     QRectF rect = QRectF(pf.x()-10,pf.y()-10,20,20);
 80     painter->drawEllipse(rect);//绘制圆形
 81     painter->drawPoint(pf);//绘制点
 82 }
 83 
 84 void myGraphicRectItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
 85 {
 86     if(event->button()== Qt::LeftButton)
 87     {
 88         m_startPos = event->pos();//鼠标左击时，获取当前鼠标在图片中的坐标，
 89         if(m_SmallRotatePolygon.containsPoint(m_startPos,Qt::WindingFill))//旋转矩形
 90         {
 91             setCursor(Qt::PointingHandCursor);
 92             m_StateFlag = ROTATE;
 93         }
 94         else if(m_insicedPolygon.containsPoint(m_startPos,Qt::WindingFill))//在矩形内框区域时按下鼠标，则可拖动图片
 95         {
 96             setCursor(Qt::ClosedHandCursor);   //改变光标形状,手的形状
 97             m_StateFlag = MOV_RECT;//标记当前为鼠标拖动图片移动状态
 98         }
 99         else if(m_leftPolygon.containsPoint(m_startPos,Qt::WindingFill))
100         {
101             setCursor(Qt::SizeHorCursor);
102             m_StateFlag = MOV_LEFT_LINE;//标记当前为用户按下矩形的左边界区域
103         }
104         else if(m_rightPolygon.containsPoint(m_startPos,Qt::WindingFill))
105         {
106             setCursor(Qt::SizeHorCursor);
107             m_StateFlag = MOV_RIGHT_LINE;//标记当前为用户按下矩形的右边界区域
108         }
109         else if(m_topPolygon.containsPoint(m_startPos,Qt::WindingFill))
110         {
111             setCursor(Qt::SizeVerCursor);
112             m_StateFlag = MOV_TOP_LINE;//标记当前为用户按下矩形的上边界区域
113         }
114         else if(m_bottomPolygon.containsPoint(m_startPos,Qt::WindingFill))
115         {
116             setCursor(Qt::SizeVerCursor);
117             m_StateFlag = MOV_BOTTOM_LINE;//标记当前为用户按下矩形的下边界区域
118         }
119 //        else if(m_rbPolygon.containsPoint(m_startPos,Qt::WindingFill))
120 //        {
121 //            setCursor(Qt::SizeFDiagCursor);
122 //            m_StateFlag = MOV_RIGHTBOTTOM_RECT;//标记当前为用户按下矩形的右下角
123 //        }
124         else
125         {
126             m_StateFlag = DEFAULT_FLAG;
127         }
128     }
129     else
130     {
131         QGraphicsItem::mousePressEvent(event);
132     }
133 }
134 
135 void myGraphicRectItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
136 {
137     if(m_StateFlag == ROTATE)
138     {
139        int nRotateAngle = atan2((event->pos().x()-m_RotateCenter.x()),(event->pos().y()-m_RotateCenter.y()))*180/M_PI;
140        SetRotate(180-nRotateAngle);
141        setRectSize(m_oldRect);
142        //qDebug()<<nRotateAngle;
143     }
144     else if(m_StateFlag == MOV_RECT)
145     {
146         QPointF point = (event->pos() - m_startPos);
147         moveBy(point.x(), point.y());
148         setRectSize(m_oldRect);
149         scene()->update();
150     }
151     else if(m_StateFlag == MOV_LEFT_LINE)
152     {
153         QPointF pf = QPointF((m_oldRectPolygon.at(1).x()+m_oldRectPolygon.at(2).x())/2,((m_oldRectPolygon.at(1).y()+m_oldRectPolygon.at(2).y())/2));
154         //计算到右侧边中点的距离
155         qreal dis = sqrt((event->pos().x()-pf.x())*(event->pos().x()-pf.x()) +(event->pos().y()-pf.y())*(event->pos().y()-pf.y()));
156         qreal dis2LT = sqrt((event->pos().x()-m_oldRectPolygon.at(0).x())*(event->pos().x()-m_oldRectPolygon.at(0).x()) +(event->pos().y()-m_oldRectPolygon.at(0).y())*(event->pos().y()-m_oldRectPolygon.at(0).y()));
157         qreal dis2RT = sqrt((event->pos().x()-m_oldRectPolygon.at(1).x())*(event->pos().x()-m_oldRectPolygon.at(1).x()) +(event->pos().y()-m_oldRectPolygon.at(1).y())*(event->pos().y()-m_oldRectPolygon.at(1).y()));
158         if(dis<16||dis2LT>dis2RT)
159         {
160             return;
161         }
162         else
163         {
164             QRectF newRect(m_oldRect);
165             newRect.setLeft(m_oldRect.right()-dis);
166             newRect.setRight(m_oldRect.right());
167             setRectSize(newRect,false);
168             m_RotateCenter=QPointF((m_oldRectPolygon.at(0).x()+m_oldRectPolygon.at(2).x())/2,(m_oldRectPolygon.at(0).y()+m_oldRectPolygon.at(2).y())/2);
169             m_oldRect.moveCenter(m_RotateCenter);
170             setRectSize(m_oldRect);
171             scene()->update();//必须要用scene()->update()，不能用update();否则会出现重影
172         }
173     }
174     else if(m_StateFlag == MOV_TOP_LINE)
175     {
176         //底边中点
177         QPointF pf = QPointF((m_oldRectPolygon.at(2).x()+m_oldRectPolygon.at(3).x())/2,((m_oldRectPolygon.at(2).y()+m_oldRectPolygon.at(3).y())/2));
178         //计算到底边中点的距离
179         qreal dis = sqrt((event->pos().x()-pf.x())*(event->pos().x()-pf.x()) +(event->pos().y()-pf.y())*(event->pos().y()-pf.y()));
180         qreal dis2LT = sqrt((event->pos().x()-m_oldRectPolygon.at(0).x())*(event->pos().x()-m_oldRectPolygon.at(0).x()) +(event->pos().y()-m_oldRectPolygon.at(0).y())*(event->pos().y()-m_oldRectPolygon.at(0).y()));
181         qreal dis2LB = sqrt((event->pos().x()-m_oldRectPolygon.at(3).x())*(event->pos().x()-m_oldRectPolygon.at(3).x()) +(event->pos().y()-m_oldRectPolygon.at(3).y())*(event->pos().y()-m_oldRectPolygon.at(3).y()));
182         if(dis<16||dis2LT>dis2LB)
183         {
184             return;
185         }
186         else
187         {
188             QRectF newRect(m_oldRect);
189             newRect.setTop(m_oldRect.bottom()-dis);
190             newRect.setBottom(m_oldRect.bottom());
191             setRectSize(newRect,false);
192             m_RotateCenter=QPointF((m_oldRectPolygon.at(0).x()+m_oldRectPolygon.at(2).x())/2,(m_oldRectPolygon.at(0).y()+m_oldRectPolygon.at(2).y())/2);
193             m_oldRect.moveCenter(m_RotateCenter);
194             setRectSize(m_oldRect);
195             scene()->update();//必须要用scene()->update()，不能用update();否则会出现重影
196         }
197     }
198     else if(m_StateFlag == MOV_RIGHT_LINE)
199     {
200         QPointF pf = QPointF((m_oldRectPolygon.at(0).x()+m_oldRectPolygon.at(3).x())/2,((m_oldRectPolygon.at(0).y()+m_oldRectPolygon.at(3).y())/2));
201         //计算到左侧边中点的距离
202         qreal dis = sqrt((event->pos().x()-pf.x())*(event->pos().x()-pf.x()) +(event->pos().y()-pf.y())*(event->pos().y()-pf.y()));
203         qreal dis2LT = sqrt((event->pos().x()-m_oldRectPolygon.at(0).x())*(event->pos().x()-m_oldRectPolygon.at(0).x()) +(event->pos().y()-m_oldRectPolygon.at(0).y())*(event->pos().y()-m_oldRectPolygon.at(0).y()));
204         qreal dis2RT = sqrt((event->pos().x()-m_oldRectPolygon.at(1).x())*(event->pos().x()-m_oldRectPolygon.at(1).x()) +(event->pos().y()-m_oldRectPolygon.at(1).y())*(event->pos().y()-m_oldRectPolygon.at(1).y()));
205         if(dis<16||dis2LT<dis2RT)
206         {
207             return;
208         }
209         else
210         {
211             QRectF newRect(m_oldRect);
212             newRect.setLeft(m_oldRect.left());
213             newRect.setRight(m_oldRect.left()+dis);
214             setRectSize(newRect,false);
215             m_RotateCenter=QPointF((m_oldRectPolygon.at(0).x()+m_oldRectPolygon.at(2).x())/2,(m_oldRectPolygon.at(0).y()+m_oldRectPolygon.at(2).y())/2);
216             m_oldRect.moveCenter(m_RotateCenter);
217             setRectSize(m_oldRect);
218             scene()->update();//必须要用scene()->update()，不能用update();否则会出现重影
219         }
220     }
221     else if(m_StateFlag == MOV_BOTTOM_LINE)
222     {
223         //顶边中点
224         QPointF pf = QPointF((m_oldRectPolygon.at(0).x()+m_oldRectPolygon.at(1).x())/2,((m_oldRectPolygon.at(0).y()+m_oldRectPolygon.at(1).y())/2));
225         //计算到底边中点的距离
226         qreal dis = sqrt((event->pos().x()-pf.x())*(event->pos().x()-pf.x()) +(event->pos().y()-pf.y())*(event->pos().y()-pf.y()));
227         qreal dis2LT = sqrt((event->pos().x()-m_oldRectPolygon.at(0).x())*(event->pos().x()-m_oldRectPolygon.at(0).x()) +(event->pos().y()-m_oldRectPolygon.at(0).y())*(event->pos().y()-m_oldRectPolygon.at(0).y()));
228         qreal dis2LB = sqrt((event->pos().x()-m_oldRectPolygon.at(3).x())*(event->pos().x()-m_oldRectPolygon.at(3).x()) +(event->pos().y()-m_oldRectPolygon.at(3).y())*(event->pos().y()-m_oldRectPolygon.at(3).y()));
229         if(dis<16||dis2LT<dis2LB)
230         {
231             return;
232         }
233         else
234         {
235             QRectF newRect(m_oldRect);
236             newRect.setTop(m_oldRect.top());
237             newRect.setBottom(m_oldRect.top()+dis);
238             setRectSize(newRect,false);
239             m_RotateCenter=QPointF((m_oldRectPolygon.at(0).x()+m_oldRectPolygon.at(2).x())/2,(m_oldRectPolygon.at(0).y()+m_oldRectPolygon.at(2).y())/2);
240             m_oldRect.moveCenter(m_RotateCenter);
241             setRectSize(m_oldRect);
242             scene()->update();//必须要用scene()->update()，不能用update();否则会出现重影
243         }
244     }
245 }
246 
247 void myGraphicRectItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
248 {
249     setCursor(Qt::ArrowCursor);
250     if(m_StateFlag == MOV_RECT)
251     {
252         m_StateFlag = DEFAULT_FLAG;
253     }
254     else {
255         QGraphicsItem::mouseReleaseEvent(event);
256     }
257 }
258 
259 void myGraphicRectItem::SetRotate(qreal RotateAngle, QPointF ptCenter)
260 {
261     m_bRotate = true;
262     if(ptCenter.x()==-999 && ptCenter.y()==-999)
263     {
264         m_RotateCenter = QPointF(m_oldRect.x()+m_oldRect.width()/2,m_oldRect.y()+m_oldRect.height()/2);
265     }
266     else
267     {
268         m_RotateCenter = ptCenter;
269     }
270     m_RotateAngle = RotateAngle;
271     this->update();
272 }
273 
274 QPointF myGraphicRectItem::getRotatePoint(QPointF ptCenter, QPointF ptIn, qreal angle)
275 {
276     double dx = ptCenter.x();
277     double dy = ptCenter.y();
278     double x = ptIn.x();
279     double y = ptIn.y();
280     double xx,yy;
281     xx = (x-dx)*cos(angle*M_PI/180)-(y-dy)*sin(angle*M_PI/180)+dx;
282     yy = (x-dx)*sin(angle*M_PI/180)+(y-dy)*cos(angle*M_PI/180)+dy;
283 
284     return QPointF(xx,yy);
285 }
286 
287 QList<QPointF> myGraphicRectItem::getRotatePoints(QPointF ptCenter, QList<QPointF> ptIns, qreal angle)
288 {
289     QList<QPointF> lstPt;
290     for(int i = 0;i<ptIns.count();i++)
291     {
292         lstPt.append(getRotatePoint(ptCenter,ptIns.at(i),angle));
293     }
294     return lstPt;
295 }
296 
297 QPolygonF myGraphicRectItem::getRotatePolygonFromRect(QPointF ptCenter, QRectF rectIn, qreal angle)
298 {
299     QVector<QPointF> vpt;
300     QPointF pf = getRotatePoint(ptCenter,rectIn.topLeft(),angle);
301     vpt.append(pf);
302     pf = getRotatePoint(ptCenter,rectIn.topRight(),angle);
303     vpt.append(pf);
304     pf = getRotatePoint(ptCenter,rectIn.bottomRight(),angle);
305     vpt.append(pf);
306     pf = getRotatePoint(ptCenter,rectIn.bottomLeft(),angle);
307     vpt.append(pf);
308     pf = getRotatePoint(ptCenter,rectIn.topLeft(),angle);
309     vpt.append(pf);
310     return QPolygonF(vpt);
311 }
312 
313 QRectF myGraphicRectItem::getCrtPosRectToSceen()
314 {
315     QRectF retRect = QRectF(m_oldRect.x()+pos().x(),m_oldRect.y()+pos().y(),m_oldRect.width(),m_oldRect.height());
316     return retRect;
317 }
318 QRectF myGraphicRectItem::getSmallRotateRect(QPointF ptA,QPointF ptB)
319 {
320     QPointF pt = getSmallRotateRectCenter(ptA,ptB);
321     return QRectF(pt.x()-10,pt.y()-10,20,20);
322 }
323 QPointF myGraphicRectItem::getSmallRotateRectCenter(QPointF ptA,QPointF ptB)
324 {
325     QPointF ptCenter = QPointF((ptA.x()+ptB.x())/2,(ptA.y()+ptB.y())/2);//A,B点的中点C
326     //中垂线方程式为 y=x*k + b;
327     qreal x,y;//旋转图标矩形的中心
328     if(abs(ptB.y()-ptA.y())<0.1)
329     {
330         if(ptA.x()<ptB.x())//矩形左上角在上方
331         {
332             x = ptCenter.x();
333             y = ptCenter.y()-20;
334         }
335         else//矩形左上角在下方
336         {
337             x = ptCenter.x();
338             y = ptCenter.y()+20;
339         }
340     }
341     else if(ptB.y()>ptA.y())//顺时针旋转0-180
342     {
343         qreal k = (ptA.x()-ptB.x())/(ptB.y()-ptA.y());//中垂线斜率
344         qreal b = (ptA.y()+ptB.y())/2-k*(ptA.x()+ptB.x())/2;
345         //求AB线中垂线上离AB中点20个像素的点C的坐标
346         x = 20*cos(atan(k))+ptCenter.x();
347         y = k*x+b;
348     }
349     else if(ptB.y()<ptA.y())//顺时针旋转180-360
350     {
351         qreal k = (ptA.x()-ptB.x())/(ptB.y()-ptA.y());//中垂线斜率
352         qreal b = (ptA.y()+ptB.y())/2-k*(ptA.x()+ptB.x())/2;
353         //求AB线中垂线上离AB中点20个像素的点C的坐标
354         x = -20*cos(atan(k))+ptCenter.x();
355         y = k*x+b;
356     }
357     return QPointF(x,y);
358 }

posted on 2020-10-23 09:47 一杯清酒邀明月阅读(8475) 评论(7) 编辑收藏举报