TechDraw: fix extension lines of projected dimension

src/Mod/TechDraw/App/DimensionGeometry.cpp

@@ -41,6 +41,14 @@ pointPair::pointPair(const pointPair& pp)
 {
     first(pp.first());
     second(pp.second());
+    overrideFirst(pp.extensionLineFirst());
+    overrideSecond(pp.extensionLineSecond());
+}
+
+// set extension line points from argument base points
+void pointPair::setExtensionLine(const pointPair& pp){
+    overrideFirst(pp.first());
+    overrideSecond(pp.second());
 }
 
 //move the points by offset
@@ -48,6 +56,8 @@ void pointPair::move(const Base::Vector3d& offset)
 {
     m_first = m_first - offset;
     m_second = m_second - offset;
+    m_overrideFirst = m_overrideFirst - offset;
+    m_overrideSecond = m_overrideSecond - offset;
 }
 
 // project the points onto the dvp's paper plane.
@@ -55,6 +65,8 @@ void pointPair::project(const DrawViewPart* dvp)
 {
     m_first = dvp->projectPoint(m_first) * dvp->getScale();
     m_second = dvp->projectPoint(m_second) * dvp->getScale();
+    m_overrideFirst = dvp->projectPoint(m_overrideFirst) * dvp->getScale();
+    m_overrideSecond = dvp->projectPoint(m_overrideSecond) * dvp->getScale();
 }
 
 // map the points onto the dvp's XY coordinate system

src/Mod/TechDraw/App/DimensionGeometry.h

@@ -38,12 +38,26 @@ class TechDrawExport pointPair
 {
 public:
     pointPair() = default;
-    pointPair(const Base::Vector3d& point0, const Base::Vector3d& point1) { m_first = point0; m_second = point1; }
+    pointPair(const Base::Vector3d& point0, const Base::Vector3d& point1)
+        : m_first(point0)
+        , m_second(point1){};
+
+    pointPair(const Base::Vector3d& point0, const Base::Vector3d& point1,
+              const Base::Vector3d& extensionPoint0, const Base::Vector3d& extensionPoint1)
+        : m_first(point0)
+        , m_second(point1)
+        , m_useOverrideFirst(true)
+        , m_overrideFirst(extensionPoint0)
+        , m_useOverrideSecond(true)
+        , m_overrideSecond(extensionPoint1){};
+
     pointPair(const pointPair& pp);
 
     pointPair& operator=(const pointPair& pp) {
         m_first = pp.first();
         m_second = pp.second();
+        overrideFirst(pp.extensionLineFirst());
+        overrideSecond(pp.extensionLineSecond());
         return *this;
     }
 
@@ -51,6 +65,12 @@ public:
     void first(Base::Vector3d newFirst) { m_first = newFirst; }
     Base::Vector3d second() const { return m_second; }
     void second(Base::Vector3d newSecond) { m_second = newSecond; }
+    // extension line specific points
+    Base::Vector3d extensionLineFirst() const { return m_useOverrideFirst ? m_overrideFirst : m_first; }
+    void overrideFirst(Base::Vector3d newFirst) { m_useOverrideFirst = true;  m_overrideFirst = newFirst; }
+    Base::Vector3d extensionLineSecond() const { return m_useOverrideSecond ? m_overrideSecond : m_second; }
+    void overrideSecond(Base::Vector3d newSecond) { m_useOverrideSecond = true;  m_overrideSecond = newSecond; }
+    void setExtensionLine(const pointPair& pp);
 
     void move(const Base::Vector3d& offset);
     void project(const DrawViewPart* dvp);
@@ -61,6 +81,11 @@ public:
 private:
     Base::Vector3d m_first;
     Base::Vector3d m_second;
+    // extension line specific points
+    bool m_useOverrideFirst = false;
+    Base::Vector3d m_overrideFirst;
+    bool m_useOverrideSecond = false;
+    Base::Vector3d m_overrideSecond;
 };
 
 //a convenient container for angular dimension points

src/Mod/TechDraw/App/DrawViewDimension.cpp

@@ -766,7 +766,9 @@ pointPair DrawViewDimension::getPointsEdgeVert(ReferenceVector references)
                 auto p2 = Base::Vector3d(projector.NearestPoint().X()
                                          , projector.NearestPoint().Y()
                                          , 0.0);
-                return pointPair(p1, p2);
+                pointPair result = pointPair(p1, p2);
+                result.setExtensionLine(closestPoints(edge->getOCCEdge(), vertex->getOCCVertex()));
+                return result;
         }
         else {
                 // unable to project

src/Mod/TechDraw/Gui/QGIViewDimension.cpp

@@ -2112,7 +2112,7 @@ void QGIViewDimension::drawDistance(TechDraw::DrawViewDimension* dimension,
                              dimension->ExtensionAngle.getValue() * M_PI / 180.0);
     }
     else {
-        drawDistanceExecutive(fromQtApp(linePoints.first()), fromQtApp(linePoints.second()),
+        drawDistanceExecutive(fromQtApp(linePoints.extensionLineFirst()), fromQtApp(linePoints.extensionLineSecond()),
                               lineAngle, labelRectangle, standardStyle, renderExtent, flipArrows);
     }
 }