TechDraw: Enable snapping section views to their base views.

src/Mod/TechDraw/App/DrawViewSection.cpp

@@ -932,27 +932,29 @@ std::vector<TechDraw::FacePtr> DrawViewSection::makeTDSectionFaces(TopoDS_Compou
 std::pair<Base::Vector3d, Base::Vector3d> DrawViewSection::sectionLineEnds()
 {
     std::pair<Base::Vector3d, Base::Vector3d> result;
-    Base::Vector3d stdZ(0.0, 0.0, 1.0);
-    double baseRotation = getBaseDVP()->Rotation.getValue();// Qt degrees are clockwise
-    Base::Rotation rotator(stdZ, baseRotation * M_PI / 180.0);
-    Base::Rotation unrotator(stdZ, -baseRotation * M_PI / 180.0);
 
+    Base::Vector3d dir = getSectionDirectionOnBaseView();
+
+    Base::Vector3d sectionOrg = SectionOrigin.getValue() - getBaseDVP()->getOriginalCentroid();
+    sectionOrg = getBaseDVP()->projectPoint(sectionOrg);// convert to base view CS
+    double halfSize = (getBaseDVP()->getSizeAlongVector(dir) / 2.0) * SectionLineStretch.getValue();
+    result.first = sectionOrg + dir * halfSize;
+    result.second = sectionOrg - dir * halfSize;
+
+    return result;
+}
+
+// calculate the direction of the section in 2d on the base view.
+Base::Vector3d DrawViewSection::getSectionDirectionOnBaseView()
+{
     auto sNorm = SectionNormal.getValue();
     auto axis = getBaseDVP()->Direction.getValue();
-    Base::Vector3d stdOrg(0.0, 0.0, 0.0);
     Base::Vector3d sectionLineDir = -axis.Cross(sNorm);
     sectionLineDir.Normalize();
     sectionLineDir = getBaseDVP()->projectPoint(sectionLineDir);// convert to base view CS
     sectionLineDir.Normalize();
 
-    Base::Vector3d sectionOrg = SectionOrigin.getValue() - getBaseDVP()->getOriginalCentroid();
-    sectionOrg = getBaseDVP()->projectPoint(sectionOrg);// convert to base view
-                                                        // CS
-    double halfSize = (getBaseDVP()->getSizeAlongVector(sectionLineDir) / 2.0) * SectionLineStretch.getValue();
-    result.first = sectionOrg + sectionLineDir * halfSize;
-    result.second = sectionOrg - sectionLineDir * halfSize;
-
-    return result;
+    return sectionLineDir;
 }
 
 // find the points and directions to make the change point marks.

src/Mod/TechDraw/App/DrawViewSection.h

@@ -165,6 +165,7 @@ public:
     static const char* CutSurfaceEnums[];
 
     virtual std::pair<Base::Vector3d, Base::Vector3d> sectionLineEnds();
+    Base::Vector3d getSectionDirectionOnBaseView();
     virtual ChangePointVector getChangePointsFromSectionLine();
 
     bool showSectionEdges(void);

src/Mod/TechDraw/Gui/QGIView.cpp

@@ -41,6 +41,8 @@
 #include <Mod/TechDraw/App/DrawPage.h>
 #include <Mod/TechDraw/App/DrawProjGroup.h>
 #include <Mod/TechDraw/App/DrawProjGroupItem.h>
+#include <Mod/TechDraw/App/DrawViewSection.h>
+#include <Mod/TechDraw/App/DrawViewPart.h>
 #include <Mod/TechDraw/App/DrawUtil.h>
 #include <Mod/TechDraw/App/DrawView.h>
 
@@ -71,7 +73,8 @@ QGIView::QGIView()
     :QGraphicsItemGroup(),
      viewObj(nullptr),
      m_innerView(false),
-     m_multiselectActivated(false)
+     m_multiselectActivated(false),
+     snapping(false)
 {
     setCacheMode(QGraphicsItem::NoCache);
     setHandlesChildEvents(false);
@@ -153,10 +156,9 @@ void QGIView::alignTo(QGraphicsItem*item, const QString &alignment)
 
 QVariant QGIView::itemChange(GraphicsItemChange change, const QVariant &value)
 {
-    QPointF newPos(0.0, 0.0);
 //    Base::Console().Message("QGIV::itemChange(%d)\n", change);
     if(change == ItemPositionChange && scene()) {
-        newPos = value.toPointF();            //position within parent!
+        QPointF newPos = value.toPointF();            //position within parent!
 
         TechDraw::DrawView *viewObj = getViewObject();
         auto* dpgi = dynamic_cast<TechDraw::DrawProjGroupItem*>(viewObj);
@@ -181,7 +183,9 @@ QVariant QGIView::itemChange(GraphicsItemChange change, const QVariant &value)
         // tell the feature that we have moved
         Gui::ViewProvider *vp = getViewProvider(viewObj);
         if (vp && !vp->isRestoring()) {
+            snapping = true; // avoid triggering updateView by the VP updateData
             viewObj->setPosition(Rez::appX(newPos.x()), Rez::appX(-newPos.y()));
+            snapping = false;
         }
 
         return newPos;
@@ -201,7 +205,7 @@ QVariant QGIView::itemChange(GraphicsItemChange change, const QVariant &value)
     return QGraphicsItemGroup::itemChange(change, value);
 }
 
-void QGIView::snapPosition(QPointF& pos)
+void QGIView::snapPosition(QPointF& mPos)
 {
     // For general views we check if the view is close to aligned vertically or horizontally to another view.
 
@@ -220,20 +224,65 @@ void QGIView::snapPosition(QPointF& pos)
     }
 
     std::vector<QGIView*> views = scenePage->getViews();
-
     qreal snapPercent = 0.05;
+
+    auto* sectionView = dynamic_cast<TechDraw::DrawViewSection*>(getViewObject());
+    if (sectionView) {
+        auto* baseView = sectionView->getBaseDVP();
+        if (!baseView) { return; }
+
+        Base::Vector3d dir3d = sectionView->getSectionDirectionOnBaseView();
+        double bSize = Rez::guiX(baseView->getSizeAlongVector(dir3d));
+        double sSize = Rez::guiX(sectionView->getSizeAlongVector(dir3d));
+
+        auto* vpdv = dynamic_cast<ViewProviderDrawingView*>(getViewProvider(baseView));
+        if (!vpdv) { return; }
+        auto* qgiv(dynamic_cast<QGIView*>(vpdv->getQView()));
+        if (!qgiv) { return; }
+        QPointF bvPos = qgiv->pos();
+        Base::Vector2d bvPt(bvPos.x(), bvPos.y());
+        Base::Vector2d mPt(mPos.x(), mPos.y());
+        Base::Vector2d dir(dir3d.x, dir3d.y);
+        if (dir.Length() < Precision::Confusion()) { return; }
+        dir.Normalize();
+
+        double snapDist = bSize * snapPercent;
+
+        Base::Vector2d projPt;
+        projPt.ProjectToLine(mPt - bvPt, dir);
+        projPt = projPt + bvPt;
+
+        Base::Vector2d v = (projPt - bvPt) + 0.5 * (sSize - bSize) * dir;
+        int sign = v * dir > 0 ? - 1 : 1;
+        double dist = v.Length();
+        if (dist < snapDist) {
+            v = dist * dir;
+            mPos = mPos + sign * QPointF(v.x, v.y);
+            return;
+        }
+
+       v = (projPt - bvPt) + 0.5 * (bSize - sSize) * dir;
+        sign = v * dir > 0 ? - 1 : 1;
+        dist = v.Length();
+        if (dist < snapDist) {
+            v = dist * dir;
+            mPos = mPos + sign * QPointF(v.x, v.y);
+            return;
+        }
+    }
+
     for (auto* view : views) {
         if (view == this) { continue; }
 
         QPointF vPos = view->pos();
         qreal dx = view->boundingRect().width() * snapPercent;
         qreal dy = view->boundingRect().height() * snapPercent;
-        if (fabs(pos.x() - vPos.x()) < dx) {
-            pos.setX(vPos.x());
+        if (fabs(mPos.x() - vPos.x()) < dx) {
+            mPos.setX(vPos.x());
             break;
         }
-        else if (fabs(pos.y() - vPos.y()) < dy) {
-            pos.setY(vPos.y());
+        else if (fabs(mPos.y() - vPos.y()) < dy) {
+            mPos.setY(vPos.y());
             break;
         }
     }

src/Mod/TechDraw/Gui/QGIView.h

@@ -122,6 +122,7 @@ public:
     void isInnerView(bool state) { m_innerView = state; }
     QGIViewClip* getClipGroup();
 
+    bool isSnapping() { return snapping; }
     void snapPosition(QPointF& position);
 
     void alignTo(QGraphicsItem*, const QString &alignment);
@@ -182,6 +183,7 @@ private:
     QHash<QString, QGraphicsItem*> alignHash;
     bool m_innerView;                                                  //View is inside another View
     bool m_multiselectActivated;
+    bool snapping;
 
     QPen m_pen;
     QBrush m_brush;

src/Mod/TechDraw/Gui/ViewProviderDrawingView.cpp

@@ -227,7 +227,7 @@ void ViewProviderDrawingView::updateData(const App::Property* prop)
     if (prop == &obj->X
         || prop == &obj->Y) {
         QGIView* qgiv = getQView();
-        if (qgiv) {
+        if (qgiv && !qgiv->isSnapping()) {
             qgiv->QGIView::updateView(true);
 
             // Update also the owner/parent view, if there is any