Pcbnew: fix 45-degree snapping of ruler and dimension tools

This introduces a new util function in geometry_utils which snaps a vector
to axes or 45 degree lines. This can be used whenever you want to
snap a vector to these angles, but still want it to stay on a grid.

This snapping is used for the dimension tool and the ruler tool.

This is substantially simpler for two-point tools that the method
used by the line tool, which uses DIRECTION_45.

Fixes: lp:1780826
https://bugs.launchpad.net/kicad/+bug/1780826

include/geometry/geometry_utils.h

@@ -30,6 +30,8 @@
 #ifndef GEOMETRY_UTILS_H
 #define GEOMETRY_UTILS_H
 
+#include <math/vector2d.h>
+
 /**
  * @return the number of segments to approximate a arc by segments
  * with a given max error (this number is >= 1)
@@ -53,6 +55,45 @@ int GetArcToSegmentCount( int aRadius, int aErrorMax, double aArcAngleDegree );
  */
 double GetCircletoPolyCorrectionFactor( int aSegCountforCircle );
 
+/**
+ * Snap a vector onto the nearest 0, 45 or 90 degree line.
+ *
+ * The magnitude of the vector is NOT kept, instead the co-ordinates are
+ * set equal (and/or opposite) or to zero as needed. The effect of this is
+ * that if the starting vector is on a square grid, the resulting snapped
+ * vector will still be on the same grid.
+
+ * @param a vector to be snapped
+ * @return the snapped vector
+ */
+template<typename T>
+VECTOR2<T> GetVectorSnapped45( const VECTOR2<T>& aVec )
+{
+    auto newVec = aVec;
+    const VECTOR2<T> absVec { std::abs( aVec.x ), std::abs( aVec.y ) };
+
+    if ( absVec.x > absVec.y * 2 )
+    {
+        // snap along x-axis
+        newVec.y = 0;
+    }
+    else if ( absVec.y > absVec.x * 2 )
+    {
+        // snap onto y-axis
+        newVec.x = 0;
+    }
+    else if ( absVec.x > absVec.y )
+    {
+        // snap away from x-axis towards 45
+        newVec.y = std::copysign( aVec.x, aVec.y );
+    } else
+    {
+        // snap away from y-axis towards 45
+        newVec.x = std::copysign( aVec.y, aVec.x );
+    }
+
+    return newVec;
+}
 
 #endif  // #ifndef GEOMETRY_UTILS_H
 

include/preview_items/two_point_geom_manager.h

@@ -25,7 +25,7 @@
 #define PREVIEW_ITEMS_TWO_POINT_GEOMETRY_MANAGER_H
 
 #include <math/vector2d.h>
-#include <common.h>
+#include <geometry/geometry_utils.h>
 
 namespace KIGFX
 {
@@ -63,11 +63,7 @@ public:
     {
         if( m_angleSnap )
         {
-            const auto vec = aEnd - m_origin;
+            m_end = GetVectorSnapped45( aEnd - m_origin ) + m_origin;
-            const auto len = vec.EuclideanNorm();
-            const auto angle = KiROUND( vec.Angle() / M_PI_4 ) * M_PI_4;
-
-            m_end = m_origin + VECTOR2I( len, 0 ).Rotate( angle );
         }
         else
         {

pcbnew/tools/drawing_tool.cpp

@@ -40,6 +40,7 @@
 #include <gal/graphics_abstraction_layer.h>
 #include <tool/tool_manager.h>
 #include <geometry/direction45.h>
+#include <geometry/geometry_utils.h>
 #include <ratsnest_data.h>
 #include <board_commit.h>
 #include <scoped_set_reset.h>
@@ -478,12 +479,10 @@ int DRAWING_TOOL::PlaceText( const TOOL_EVENT& aEvent )
 
 void DRAWING_TOOL::constrainDimension( DIMENSION* dimension )
 {
-    VECTOR2I lineVector( dimension->GetEnd() - dimension->GetOrigin() );
+    const VECTOR2I lineVector{ dimension->GetEnd() - dimension->GetOrigin() };
-    double angle = lineVector.Angle();
-    double newAngle = KiROUND( angle / M_PI_4 ) * M_PI_4;
-    VECTOR2I newLineVector = lineVector.Rotate( newAngle - angle );
 
-    dimension->SetEnd( dimension->GetOrigin() + static_cast<wxPoint>( newLineVector ) );
+    dimension->SetEnd( wxPoint(
+        VECTOR2I( dimension->GetOrigin() ) + GetVectorSnapped45( lineVector ) ) );
 }