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

2024-07-11 04:42:00   221人阅读

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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



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