Qt obtains the intersection of a polygon (qgraphicspolympus gonitem) or a QT graphical component and a straight line (qlinef ).

Sometimes it is necessary to obtain the intersection between a straight line and various graphics, including polygon and various QT graphic boxes.

For example, to keep the connection line on the side of a polygon and point to the center of the polygon, we need to obtain the intersection of the AB and polygon of the line.

1. intersection of a polygon (qgraphicspolympus gonitem) and a straight line (qlinef)

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// Known points and polygon // points A and B can be obtained through boundingrect (). Width ()/2 of polygon;QPointF A;QPointF B;QGraphicsPolygonItem yellowItem;  QLineF lineAB(A,B); // AB connection qpointf Arrowpoint; // you can specify the intersection.QPolygonF yellowtPolygon = yellowItem->polygon();QPointF p1 = yellowtPolygon.first() + yellowItem->pos();// Traverse each edge line for (INT I = 1; I <yellowtpolygon. count (); ++ I) {qpointf P2 = yellowtpolygon. at (I) + yellowitem-> pos ();QLineF polyLine = QLineF(p1, p2);  // Core: Determine whether the intersection is qlinef: intersecttype = polyline. Intersect (lineab, & Arrowpoint); If (intersecttype = qlinef: boundedintersection) break;p1 = p2;}  // Arrowpoint is the intersection.

From the code above, we can see that the intersection of a polygon and a straight line is to traverse the connection between a straight line and all edges. by extension, all QT graphical components, such as qpushbutton and qqgraphicstextitem, the intersection of a graphic component with a boundary can be obtained. That is, you can traverse the intersection of all edges and straight lines.

2. Intersection of QT graphical components and qlinef

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QPointF A;QPointF B;QLineF lineAB(A,B); // AB connectionQ: common component m_commentitem;  qreal commentWidth  = m_CommentItem->boundingRect().width();qreal commentHeight = m_CommentItem->boundingRect().height();  QPointF intersectPoint;// Four Edges-four lines qlinef line1 (, 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);  // Traverse four lines of foreach(QLineF oneline,lineList){QLineF::IntersectType intersectType = oneline.intersect(lineAB, &intersectPoint); if (intersectType == QLineF::BoundedIntersection) break;}  // Intersectpoint is the intersection point

3. Example:

Qt examples and Demos-> graphics view-> dimo-scene

From Weizhi note (wiz)