Add the Move Parallel Tool

resources.qrc

@@ -26,6 +26,7 @@
         <file>images/cursor-georeferencing-move.png</file>
         <file>images/cursor-hollow.png</file>
         <file>images/cursor-invisible.png</file>
+        <file>images/cursor-move-parallel.png</file>
         <file>images/cursor-rotate.png</file>
         <file>images/cursor-scale.png</file>
         <file>images/cut.png</file>
@@ -102,6 +103,7 @@
         <file>images/tool-fill-border.png</file>
         <file>images/tool-gps-display.png</file>
         <file>images/tool-measure.png</file>
+        <file>images/tool-move-parallel.png</file>
         <file>images/tool-rotate.png</file>
         <file>images/tool-rotate-pattern.png</file>
         <file>images/tool-scale.png</file>

src/CMakeLists.txt

@@ -240,6 +240,7 @@ set(Mapper_Common_SRCS
   tools/object_selector.cpp
   tools/pan_tool.cpp
   tools/point_handles.cpp
+  tools/move_parallel_tool.cpp
   tools/rotate_tool.cpp
   tools/rotate_pattern_tool.cpp
   tools/scale_tool.cpp

src/core/objects/object.cpp

@@ -1160,7 +1160,7 @@ ClosestPathCoord PathObject::findClosestPointTo(
 
 	using distance_type = decltype(ClosestPathCoord::distance_squared);
 	return std::accumulate(begin(path_parts), end(path_parts),
-	                       ClosestPathCoord { {}, std::numeric_limits<distance_type>::max() },
+	                       ClosestPathCoord { {}, {}, std::numeric_limits<distance_type>::max() },
 	                       op);
 }
 

src/core/path_coord.h

@@ -158,11 +158,17 @@ class PathCoord
 
 
 /**
- * The structure returned when looking for closest coordinates on a path.
+ * The structure returned when looking for the closest coordinates on a path.
+ * The tangent element is defined even on corners and line ends. Following the
+ * intuitive view, the tangent line touches the corner, dividing the plane into
+ * the part with the corner and the part without it. At the line ends, the
+ * "tangent" is the direction of the neighboring segment. The "pseudo tangent"
+ * is generated to define the direction for mouse drag actions.
  */
 struct ClosestPathCoord
 {
 	PathCoord path_coord;
+	MapCoordF tangent;
 	double distance_squared;
 };