Qt获取多边形(QGraphicsPolygonItem)或Qt图形组件与直线(QLineF)的交点 - 推酷

有时需要获取直线与各种图形的交点，包括多边形和各种Qt图形框。

例如上图中，要想使连接线始终在多边形的边上，且能指向多边形中心，那么我们就要获取连线AB与多边形的交点。

1.多边形(QGraphicsPolygonItem)与直线(QLineF)的交点

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//已知点和多边形//A、B点可通过多边形的boundingRect().width()/2获取; QPointF A; QPointF B; QGraphicsPolygonItem yellowItem;    QLineF lineAB(A,B); //AB连线QPointF arrowPoint; //设置交点 QPolygonF yellowtPolygon = yellowItem->polygon(); QPointF p1 = yellowtPolygon.first() + yellowItem->pos(); //遍历各边连线for (int i = 1; i < yellowtPolygon.count(); ++i) { QPointF p2 = yellowtPolygon.at(i) + yellowItem->pos(); QLineF polyLine = QLineF(p1, p2);    //核心：判断是否相交 QLineF::IntersectType intersectType = polyLine.intersect(lineAB, &arrowPoint); if (intersectType == QLineF::BoundedIntersection) break; p1 = p2; }    //arrowPoint 即为交点

从上面代码可以看到，一个多边形和直线的交点的实现，就是遍历直线与所有边的联系，推而广之，所有Qt的图形化组件，比如QPushButton，QQGraphicsTextItem等，只要有边界的图形化组件都能获取其与直线的交点。即遍历所有边与直线的交点即可。

2.Qt图形组件与直线(QLineF)的交点

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QPointF A; QPointF B; QLineF lineAB(A,B); //AB连线 Q普通组件 m_CommentItem;    qreal commentWidth  = m_CommentItem->boundingRect().width(); qreal commentHeight = m_CommentItem->boundingRect().height();    QPointF intersectPoint; //四个边-四条线QLineF line1(0,0,commentWidth,0 ); QLineF line2( 0,0,0 ,commentHeight); QLineF line3(commentWidth, 0 ,commentWidth,commentHeight); QLineF line4( 0 ,commentHeight,commentWidth,commentHeight); QList<QLineF> lineList; lineList.append(line1); lineList.append(line2); lineList.append(line3); lineList.append(line4);    //遍历四条线foreach (QLineF oneline,lineList) { QLineF::IntersectType intersectType = oneline.intersect(lineAB, &intersectPoint); if (intersectType == QLineF::BoundedIntersection) break ; }    //intersectPoint 即为交点

3.可参考例子：

Qt Examples and Demos -> Graphics View ->Diagram Scene

来自为知笔记(Wiz)