Grid snapping fixes.

1) Uniformly honour the GAL grid snap settings
2) Make more uniform use of GRID_HELPERs
3) Smarten EDIT_LINE for mid-point snapping

Fixes https://gitlab.com/kicad/code/kicad/issues/6558

eeschema/tools/sch_drawing_tools.cpp

@@ -855,7 +855,7 @@ int SCH_DRAWING_TOOLS::TwoClickPlace( const TOOL_EVENT& aEvent )
     {
         setCursor();
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( !evt->Modifier( MD_ALT ) );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
 
         VECTOR2I cursorPos = grid.BestSnapAnchor( controls->GetCursorPosition( false ), snapLayer,
                                                   item );

eeschema/tools/sch_line_wire_bus_tool.cpp

@@ -504,7 +504,7 @@ int SCH_LINE_WIRE_BUS_TOOL::doDrawSegments( const std::string& aTool, int aType,
     {
         setCursor();
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( !evt->Modifier( MD_ALT ) );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
 
         wxPoint cursorPos = evt->IsPrime() ? (wxPoint) evt->Position()
                                            : (wxPoint) controls->GetMousePosition();

include/tool/edit_constraints.h

@@ -32,6 +32,15 @@ class EDIT_POINT;
 class EDIT_LINE;
 class EDIT_POINTS;
 
+
+enum GRID_CONSTRAINT_TYPE
+{
+    IGNORE_GRID,
+    SNAP_TO_GRID,
+    SNAP_BY_GRID    // Keep it on grid if it started on grid (treat x and y independently)
+};
+
+
 /**
  * EDIT_CONSTRAINT
  *

include/tool/edit_points.h

@@ -30,13 +30,12 @@
 
 #include <list>
 #include <deque>
-
-#include "edit_constraints.h"
-
 #include <memory>
 
+#include "edit_constraints.h"
 #include <view/view.h>
 
+
 /**
  * EDIT_POINT
  *
@@ -55,7 +54,7 @@ public:
             m_position( aPoint ),
             m_isActive( false ),
             m_isHover( false ),
-            m_gridFree( false ),
+            m_gridConstraint( SNAP_TO_GRID ),
             m_connected( aConnected )
     {
     }
@@ -188,8 +187,8 @@ public:
     bool IsHover() const { return m_isHover; }
     void SetHover( bool aHover = true ) { m_isHover = aHover; }
 
-    bool IsGridFree() const { return m_gridFree; }
+    GRID_CONSTRAINT_TYPE GetGridConstraint() const { return m_gridConstraint; }
-    void SetGridFree( bool aGridFree = true ) { m_gridFree = aGridFree; }
+    void SetGridConstraint( GRID_CONSTRAINT_TYPE aConstraint ) { m_gridConstraint = aConstraint; }
 
     bool operator==( const EDIT_POINT& aOther ) const
     {
@@ -209,7 +208,7 @@ private:
     VECTOR2I             m_position;        // Position of EDIT_POINT
     bool                 m_isActive;        // True if this point is being manipulated
     bool                 m_isHover;         // True if this point is being hovered over
-    bool      m_gridFree;        // True if this point should not be snapped to the grid.
+    GRID_CONSTRAINT_TYPE m_gridConstraint;  // Describes the grid snapping behavior.
 
     ///> An optional connected item record used to mimic polyLine behaviour with individual
     /// line segments.
@@ -241,8 +240,7 @@ public:
         m_origin( aOrigin ),
         m_end( aEnd )
     {
-        // Don't snap the line center to the grid
+        SetGridConstraint( SNAP_BY_GRID );
-        SetGridFree();
     }
 
     ///> @copydoc EDIT_POINT::GetPosition()

pcbnew/tools/drawing_tool.cpp

@@ -694,7 +694,7 @@ int DRAWING_TOOL::DrawDimension( const TOOL_EVENT& aEvent )
         setCursor();
 
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( m_frame->IsGridVisible() );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         VECTOR2I cursorPos = evt->IsPrime() ? evt->Position() : m_controls->GetMousePosition();
         cursorPos = grid.BestSnapAnchor( cursorPos, nullptr );
         m_controls->ForceCursorPosition( true, cursorPos );
@@ -1184,7 +1184,7 @@ int DRAWING_TOOL::SetAnchor( const TOOL_EVENT& aEvent )
         setCursor();
 
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( m_frame->IsGridVisible() );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         VECTOR2I cursorPos = grid.BestSnapAnchor( m_controls->GetMousePosition(),
                                                   LSET::AllLayersMask() );
         m_controls->ForceCursorPosition( true, cursorPos );
@@ -1297,7 +1297,7 @@ bool DRAWING_TOOL::drawSegment( const std::string& aTool, PCB_SHAPE** aGraphic,
             m_frame->SetMsgPanel( graphic );
 
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( m_frame->IsGridVisible() );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         cursorPos = grid.BestSnapAnchor( m_controls->GetMousePosition(), m_frame->GetActiveLayer() );
         m_controls->ForceCursorPosition( true, cursorPos );
 
@@ -1593,7 +1593,7 @@ bool DRAWING_TOOL::drawArc( const std::string& aTool, PCB_SHAPE** aGraphic, bool
         graphic->SetLayer( layer );
 
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( m_frame->IsGridVisible() );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         VECTOR2I cursorPos = grid.BestSnapAnchor( m_controls->GetMousePosition(), graphic );
         m_controls->ForceCursorPosition( true, cursorPos );
 
@@ -1878,7 +1878,7 @@ int DRAWING_TOOL::DrawZone( const TOOL_EVENT& aEvent )
 
         LSET layers( m_frame->GetActiveLayer() );
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( m_frame->IsGridVisible() );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         VECTOR2I cursorPos = grid.BestSnapAnchor( evt->IsPrime() ? evt->Position()
                                                                  : m_controls->GetMousePosition(),
                                                   layers );

pcbnew/tools/edit_tool.cpp

@@ -416,7 +416,7 @@ int EDIT_TOOL::doMoveSelection( TOOL_EVENT aEvent, bool aPickReference )
         VECTOR2I movement;
         editFrame->GetCanvas()->SetCurrentCursor( KICURSOR::MOVING );
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( !evt->Modifier( MD_ALT ) );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
 
         if( evt->IsAction( &PCB_ACTIONS::move ) || evt->IsMotion() || evt->IsDrag( BUT_LEFT )
                 || evt->IsAction( &ACTIONS::refreshPreview )

pcbnew/tools/pcb_viewer_tools.cpp

@@ -233,7 +233,7 @@ int PCB_VIEWER_TOOLS::MeasureTool( const TOOL_EVENT& aEvent )
     {
         setCursor();
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( !evt->Modifier( MD_ALT ) );
+        grid.SetUseGrid( view.GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         const VECTOR2I cursorPos = grid.BestSnapAnchor( controls.GetMousePosition(), nullptr );
         controls.ForceCursorPosition(true, cursorPos );
 

pcbnew/tools/pcbnew_picker_tool.cpp

@@ -67,7 +67,7 @@ int PCBNEW_PICKER_TOOL::Main( const TOOL_EVENT& aEvent )
         setCursor();
 
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( !evt->Modifier( MD_ALT ) );
+        grid.SetUseGrid( getView()->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
         VECTOR2I cursorPos = grid.BestSnapAnchor( controls->GetMousePosition(), nullptr );
         controls->ForceCursorPosition(true, cursorPos );
 

pcbnew/tools/point_editor.cpp

@@ -171,7 +171,7 @@ public:
                 points->Point( ARC_MID ).SetConstraint( new EC_LINE( points->Point( ARC_MID ),
                                                                      points->Point( ARC_CENTER ) ) );
 
-                points->Point( ARC_MID ).SetGridFree();
+                points->Point( ARC_MID ).SetGridConstraint( IGNORE_GRID );
                 break;
 
             case S_CIRCLE:
@@ -437,11 +437,13 @@ int POINT_EDITOR::OnSelectionChange( const TOOL_EVENT& aEvent )
     while( TOOL_EVENT* evt = Wait() )
     {
         grid.SetSnap( !evt->Modifier( MD_SHIFT ) );
-        grid.SetUseGrid( editFrame->IsGridVisible() );
+        grid.SetUseGrid( view->GetGAL()->GetGridSnapping() && !evt->Modifier( MD_ALT ) );
 
         if( !m_editPoints || evt->IsSelectionEvent() ||
                 evt->Matches( EVENTS::InhibitSelectionEditing ) )
+        {
             break;
+        }
 
         EDIT_POINT* prevHover = m_hoveredPoint;
 
@@ -469,14 +471,46 @@ int POINT_EDITOR::OnSelectionChange( const TOOL_EVENT& aEvent )
             }
 
             //TODO: unify the constraints to solve simultaneously instead of sequentially
-            if( m_editedPoint->IsGridFree() )
+            switch( m_editedPoint->GetGridConstraint() )
             {
+            case IGNORE_GRID:
                 m_editedPoint->SetPosition( evt->Position() );
-            }
+                break;
-            else
+
-            {
+            case SNAP_TO_GRID:
                 m_editedPoint->SetPosition( grid.BestSnapAnchor( evt->Position(), snapLayers,
                                                                  { item } ) );
+                break;
+
+            case SNAP_BY_GRID:
+            {
+                VECTOR2I start = m_editedPoint->GetPosition();
+                VECTOR2I startGrid = grid.BestSnapAnchor( start, snapLayers, { item } );
+                VECTOR2I end = evt->Position();
+                VECTOR2I endGrid = grid.BestSnapAnchor( end, snapLayers, { item } );
+
+                if( start == startGrid )
+                {
+                    end = endGrid;
+                }
+                else if( start.x == startGrid.x )
+                {
+                    end.x = endGrid.x;
+
+                    if( abs( end.y - start.y ) < grid.GetGrid().y )
+                        end.y = start.y;
+                }
+                else if( start.y == startGrid.y )
+                {
+                    end.y = endGrid.y;
+
+                    if( abs( end.x - start.x ) < grid.GetGrid().x )
+                        end.x = start.x;
+                }
+
+                m_editedPoint->SetPosition( end );
+            }
+                break;
             }
 
             // The alternative constraint limits to 45°
@@ -487,12 +521,13 @@ int POINT_EDITOR::OnSelectionChange( const TOOL_EVENT& aEvent )
             else
                 m_editedPoint->ApplyConstraint();
 
-            if( !m_editedPoint->IsGridFree() )
+            if( m_editedPoint->GetGridConstraint() == SNAP_TO_GRID )
             {
                 m_editedPoint->SetPosition( grid.BestSnapAnchor( m_editedPoint->GetPosition(),
                                                                  snapLayers, { item } ) );
             }
 
+            controls->ForceCursorPosition( true, m_editedPoint->GetPosition() );
             updateItem();
             updatePoints();
         }