diff --git a/common/drawframe.cpp b/common/drawframe.cpp
index 1b87bf70c8..83c1090456 100644
--- a/common/drawframe.cpp
+++ b/common/drawframe.cpp
@@ -146,6 +146,7 @@ void EDA_DRAW_FRAME::EraseMsgBox()
 void EDA_DRAW_FRAME::OnActivate( wxActivateEvent& event )
 {
     m_FrameIsActive = event.GetActive();
+
     if( DrawPanel )
         DrawPanel->m_CanStartBlock = -1;
 
@@ -157,6 +158,7 @@ void EDA_DRAW_FRAME::OnMenuOpen( wxMenuEvent& event )
 {
     if( DrawPanel )
         DrawPanel->m_CanStartBlock = -1;
+
     event.Skip();
 }
 
@@ -197,6 +199,7 @@ void EDA_DRAW_FRAME::PrintPage( wxDC* aDC,int aPrintMask,
     wxMessageBox( wxT("EDA_DRAW_FRAME::PrintPage() error"));
 }
 
+
 // Virtual function
 void EDA_DRAW_FRAME::OnSelectGrid( wxCommandEvent& event )
 {
@@ -253,7 +256,7 @@ void EDA_DRAW_FRAME::OnSelectGrid( wxCommandEvent& event )
      * index returned by GetSelection().
      */
     m_LastGridSizeId = id - ID_POPUP_GRID_LEVEL_1000;
-    screen->m_Curseur = DrawPanel->GetScreenCenterRealPosition();
+    screen->m_Curseur = DrawPanel->GetScreenCenterLogicalPosition();
     screen->SetGrid( id );
     Refresh();
 }
@@ -285,9 +288,11 @@ void EDA_DRAW_FRAME::OnSelectZoom( wxCommandEvent& event )
     {
         id--;
         int selectedZoom = GetBaseScreen()->m_ZoomList[id];
+
         if( GetBaseScreen()->GetZoom() == selectedZoom )
             return;
-        GetBaseScreen()->m_Curseur = DrawPanel->GetScreenCenterRealPosition();
+
+        GetBaseScreen()->m_Curseur = DrawPanel->GetScreenCenterLogicalPosition();
         GetBaseScreen()->SetZoom( selectedZoom );
         RedrawScreen( false );
     }
@@ -382,12 +387,14 @@ void EDA_DRAW_FRAME::SetToolID( int aId, int aCursor, const wxString& aToolMsg )
 {
     // Keep default cursor in toolbars
     SetCursor( wxNullCursor );
+
     // Change Cursor in DrawPanel only
     if( DrawPanel )
     {
         DrawPanel->m_PanelDefaultCursor = aCursor;
         DrawPanel->SetCursor( aCursor );
     }
+
     DisplayToolMsg( aToolMsg );
 
     if( aId < 0 )
@@ -428,6 +435,7 @@ void EDA_DRAW_FRAME::SetToolID( int aId, int aCursor, const wxString& aToolMsg )
         m_VToolBar->ToggleTool( ID_NO_SELECT_BUTT, TRUE );
 
     m_ID_current_state = aId;
+
     if( m_VToolBar )
         m_VToolBar->Refresh( );
 }
@@ -527,6 +535,7 @@ void EDA_DRAW_FRAME::AdjustScrollBars()
 
     if( posX < 0 )
         posX = 0;
+
     if( posY < 0 )
         posY = 0;
 
@@ -562,6 +571,7 @@ void EDA_DRAW_FRAME::SetLanguage( wxCommandEvent& event )
     EDA_BASE_FRAME::SetLanguage( event );
 }
 
+
 /**
  * Round to the nearest precision.
  *
@@ -575,6 +585,7 @@ double RoundTo0( double x, double precision )
     assert( precision != 0 );
 
     long long ix = wxRound( x * precision );
+
     if ( x < 0.0 )
         NEGATE( ix );
 
@@ -613,15 +624,14 @@ void EDA_DRAW_FRAME::UpdateStatusBar()
     if ( (screen->GetZoom() % screen->m_ZoomScalar) == 0 )
         Line.Printf( wxT( "Z %d" ), screen->GetZoom() / screen->m_ZoomScalar );
     else
-        Line.Printf( wxT( "Z %.1f" ),
-                     (float)screen->GetZoom() / screen->m_ZoomScalar );
+        Line.Printf( wxT( "Z %.1f" ), (float)screen->GetZoom() / screen->m_ZoomScalar );
+
     SetStatusText( Line, 1 );
 
     /* Display absolute coordinates:  */
-    double dXpos = To_User_Unit( g_UserUnit, screen->m_Curseur.x,
-                                 m_InternalUnits );
-    double dYpos = To_User_Unit( g_UserUnit, screen->m_Curseur.y,
-                                 m_InternalUnits );
+    double dXpos = To_User_Unit( g_UserUnit, screen->m_Curseur.x, m_InternalUnits );
+    double dYpos = To_User_Unit( g_UserUnit, screen->m_Curseur.y, m_InternalUnits );
+
     /*
      * Converting from inches to mm can give some coordinates due to
      * float point precision rounding errors, like 1.999 or 2.001 so
@@ -678,6 +688,7 @@ void EDA_DRAW_FRAME::UpdateStatusBar()
     dy = screen->m_Curseur.y - screen->m_O_Curseur.y;
     dXpos = To_User_Unit( g_UserUnit, dx, m_InternalUnits );
     dYpos = To_User_Unit( g_UserUnit, dy, m_InternalUnits );
+
     if( g_UserUnit == MILLIMETRES )
     {
         dXpos = RoundTo0( dXpos, (double) ( m_InternalUnits / 10 ) );
@@ -704,11 +715,15 @@ void EDA_DRAW_FRAME::LoadSettings()
     EDA_BASE_FRAME::LoadSettings();
     cfg->Read( m_FrameName + CursorShapeEntryKeyword, &m_CursorShape, ( long )0 );
     bool btmp;
+
     if ( cfg->Read( m_FrameName + ShowGridEntryKeyword, &btmp ) )
         SetGridVisibility( btmp);
+
     int itmp;
+
     if( cfg->Read( m_FrameName + GridColorEntryKeyword, &itmp ) )
         SetGridColor(itmp);
+
     cfg->Read( m_FrameName + LastGridSizeId, &m_LastGridSizeId, 0L );
 }
 
diff --git a/common/drawpanel.cpp b/common/drawpanel.cpp
index bfc24cb03e..88f57d9fb7 100644
--- a/common/drawpanel.cpp
+++ b/common/drawpanel.cpp
@@ -272,26 +272,12 @@ wxPoint EDA_DRAW_PANEL::CursorScreenPosition()
 }
 
 
-/**
- * Function GetScreenCenterRealPosition
- * @return position (in internal units) of the current area center showed
- *         on screen
- */
-wxPoint EDA_DRAW_PANEL::GetScreenCenterRealPosition( void )
+wxPoint EDA_DRAW_PANEL::GetScreenCenterLogicalPosition()
 {
-    int x, y, ppuX, ppuY;
-    wxPoint pos;
-    double  scalar = GetScreen()->GetScalingFactor();
+    wxSize size = GetClientSize() / 2;
+    INSTALL_UNBUFFERED_DC( dc, this );
 
-    GetViewStart( &x, &y );
-    GetScrollPixelsPerUnit( &ppuX, &ppuY );
-    x *= ppuX;
-    y *= ppuY;
-    pos.x = wxRound( ( (double) GetClientSize().x / 2.0 + (double) x ) / scalar );
-    pos.y = wxRound( ( (double) GetClientSize().y / 2.0 + (double) y ) / scalar );
-    pos += GetScreen()->m_DrawOrg;
-
-    return pos;
+    return wxPoint( dc.DeviceToLogicalX( size.x ), dc.DeviceToLogicalY( size.y ) );
 }
 
 
@@ -650,6 +636,15 @@ void EDA_DRAW_PANEL::DrawGrid( wxDC* DC )
 
     m_Parent->PutOnGrid( &org, &gridSize );
 
+    // Setting the nearest grid position can select grid points outside the clip box.
+    // Incrementing the start point by one grid step should prevent drawing grid points
+    // outside the clip box.
+    if( org.x < m_ClipBox.GetX() )
+        org.x += wxRound( gridSize.x );
+
+    if( org.y < m_ClipBox.GetY() )
+        org.y += wxRound( gridSize.y );
+
 #if ( defined( __WXMAC__ ) || defined( __WXGTK__ ) || 1 )
     // Use a pixel based draw to display grid.  There are a lot of calls, so the cost is high
     // and grid is slowly drawn on some platforms.  Please note that this should always be
diff --git a/common/gr_basic.cpp b/common/gr_basic.cpp
index 559547bc69..d0eb6e2726 100644
--- a/common/gr_basic.cpp
+++ b/common/gr_basic.cpp
@@ -93,7 +93,7 @@ static wxDC* s_DC_lastDC = NULL;
  *
  * Please note that this is only accurate for lines that are one pixel wide.
  *
- * @param aRect - The rectangle to test.
+ * @param aClipBox - The rectangle to test.
  * @param x1 - X coordinate of one end of a line.
  * @param y1 - Y coordinate of one end of a line.
  * @param x2 - X coordinate of the other end of a line.
diff --git a/common/zoom.cpp b/common/zoom.cpp
index 09356f68f0..1a1a307413 100644
--- a/common/zoom.cpp
+++ b/common/zoom.cpp
@@ -125,7 +125,7 @@ void EDA_DRAW_FRAME::OnZoom( wxCommandEvent& event )
 
     case ID_ZOOM_IN:
         if( id == ID_ZOOM_IN )
-            screen->m_Curseur = DrawPanel->GetScreenCenterRealPosition();
+            screen->m_Curseur = DrawPanel->GetScreenCenterLogicalPosition();
         if( screen->SetPreviousZoom() )
             RedrawScreen( zoom_at_cursor );
         break;
@@ -137,7 +137,7 @@ void EDA_DRAW_FRAME::OnZoom( wxCommandEvent& event )
 
     case ID_ZOOM_OUT:
         if( id == ID_ZOOM_OUT )
-            screen->m_Curseur = DrawPanel->GetScreenCenterRealPosition();
+            screen->m_Curseur = DrawPanel->GetScreenCenterLogicalPosition();
         if( screen->SetNextZoom() )
             RedrawScreen( zoom_at_cursor );
         break;
diff --git a/include/class_drawpanel.h b/include/class_drawpanel.h
index c43c1b8220..10d54d52b2 100644
--- a/include/class_drawpanel.h
+++ b/include/class_drawpanel.h
@@ -154,7 +154,7 @@ public:
      * converts \a aRect from device to drawing (logical) coordinates.
      * <p>
      * \a aRect must be in scrolled device units.
-     * <\p>
+     * </p>
      * @param aRect The rectangle to convert.
      * @param aDC The device context used for the conversion.
      * @return A rectangle converted to drawing units.
@@ -191,12 +191,12 @@ public:
      * area.  The clip box is used when drawing to determine which objects are not visible
      * and do not need to be drawn.
      * </p>
-     * @param aDc The device context use for drawing with the correct scale and
+     * @param aDC The device context use for drawing with the correct scale and
      *            offsets already configured.  See DoPrepareDC().
      * @param aRect The clip rectangle in device units or NULL for the entire visible area
      *              of the screen.
      */
-    void         SetClipBox( wxDC& dc, const wxRect* aRect = NULL );
+    void         SetClipBox( wxDC& aDC, const wxRect* aRect = NULL );
 
     void         ReDraw( wxDC* DC, bool erasebg = TRUE );
 
@@ -222,7 +222,12 @@ public:
      */
     void         RefreshDrawingRect( const EDA_Rect& aRect, bool aEraseBackground = true );
 
-    wxPoint      GetScreenCenterRealPosition( void );
+    /**
+     * Function GetScreenCenterLogicalPosition
+     * @return The current screen center position in logical (drawing) units.
+     */
+    wxPoint      GetScreenCenterLogicalPosition();
+
     void         MouseToCursorSchema();
     void         MouseTo( const wxPoint& Mouse );
 
diff --git a/pcbnew/editedge.cpp b/pcbnew/editedge.cpp
index 858b227498..12c754fdc4 100644
--- a/pcbnew/editedge.cpp
+++ b/pcbnew/editedge.cpp
@@ -295,8 +295,7 @@ void WinEDA_PcbFrame::End_Edge( DRAWSEGMENT* Segment, wxDC* DC )
  */
 static void Montre_Position_NewSegment( EDA_DRAW_PANEL* panel, wxDC* DC, bool erase )
 {
-    DRAWSEGMENT* Segment = (DRAWSEGMENT*)
-                           panel->GetScreen()->GetCurItem();
+    DRAWSEGMENT* Segment = (DRAWSEGMENT*) panel->GetScreen()->GetCurItem();
     int          t_fill = DisplayOpt.DisplayDrawItems;
 
     if( Segment == NULL )
@@ -309,7 +308,8 @@ static void Montre_Position_NewSegment( EDA_DRAW_PANEL* panel, wxDC* DC, bool er
 
     if( Segments_45_Only && ( Segment->m_Shape == S_SEGMENT ) )
     {
-        Calcule_Coord_Extremite_45( Segment->m_Start.x, Segment->m_Start.y,
+        Calcule_Coord_Extremite_45( panel->GetScreen()->m_Curseur,
+                                    Segment->m_Start.x, Segment->m_Start.y,
                                     &Segment->m_End.x, &Segment->m_End.y );
     }
     else    /* here the angle is arbitrary */
diff --git a/pcbnew/editrack.cpp b/pcbnew/editrack.cpp
index befd4933fb..2ff0c090fd 100644
--- a/pcbnew/editrack.cpp
+++ b/pcbnew/editrack.cpp
@@ -751,7 +751,8 @@ void ShowNewTrackWhenMovingCursor( EDA_DRAW_PANEL* panel, wxDC* DC, bool erase )
             /* Calculate of the end of the path for the permitted directions:
              * horizontal, vertical or 45 degrees.
              */
-            Calcule_Coord_Extremite_45( g_CurrentTrackSegment->m_Start.x,
+            Calcule_Coord_Extremite_45( screen->m_Curseur,
+                                        g_CurrentTrackSegment->m_Start.x,
                                         g_CurrentTrackSegment->m_Start.y,
                                         &g_CurrentTrackSegment->m_End.x,
                                         &g_CurrentTrackSegment->m_End.y );
@@ -815,15 +816,14 @@ void ShowNewTrackWhenMovingCursor( EDA_DRAW_PANEL* panel, wxDC* DC, bool erase )
 
 
 /* Determine the coordinate to advanced the the current segment
- * in 0, 90, or 45 degrees, depending on position of  origin and
- * cursor position.
+ * in 0, 90, or 45 degrees, depending on position of origin and \a aPosition.
  */
-void Calcule_Coord_Extremite_45( int ox, int oy, int* fx, int* fy )
+void Calcule_Coord_Extremite_45( const wxPoint& aPosition, int ox, int oy, int* fx, int* fy )
 {
     int deltax, deltay, angle;
 
-    deltax = ActiveScreen->m_Curseur.x - ox;
-    deltay = ActiveScreen->m_Curseur.y - oy;
+    deltax = aPosition.x - ox;
+    deltay = aPosition.y - oy;
 
     deltax = abs( deltax );
     deltay = abs( deltay );
@@ -849,7 +849,7 @@ void Calcule_Coord_Extremite_45( int ox, int oy, int* fx, int* fy )
     switch( angle )
     {
     case 0:
-        *fx = ActiveScreen->m_Curseur.x;
+        *fx = aPosition.x;
         *fy = oy;
         break;
 
@@ -858,9 +858,9 @@ void Calcule_Coord_Extremite_45( int ox, int oy, int* fx, int* fy )
         deltay = deltax;
 
         /* Recalculate the signs fo deltax and deltaY. */
-        if( ( ActiveScreen->m_Curseur.x - ox ) < 0 )
+        if( ( aPosition.x - ox ) < 0 )
             deltax = -deltax;
-        if( ( ActiveScreen->m_Curseur.y - oy ) < 0 )
+        if( ( aPosition.y - oy ) < 0 )
             deltay = -deltay;
 
         *fx = ox + deltax;
@@ -869,7 +869,7 @@ void Calcule_Coord_Extremite_45( int ox, int oy, int* fx, int* fy )
 
     case 90:
         *fx = ox;
-        *fy = ActiveScreen->m_Curseur.y;
+        *fy = aPosition.y;
         break;
     }
 }
diff --git a/pcbnew/protos.h b/pcbnew/protos.h
index d6be87881a..0792da7414 100644
--- a/pcbnew/protos.h
+++ b/pcbnew/protos.h
@@ -216,10 +216,9 @@ TRACK* LocateIntrusion( TRACK* listStart, TRACK* aTrack, int aLayer, const wxPoi
 void   ShowNewTrackWhenMovingCursor( EDA_DRAW_PANEL* panel, wxDC* DC, bool erase );
 
 /* Determine coordinate for a segment direction of 0, 90 or 45 degrees,
- * depending on it's position from the origin (ox, oy) and the current
- * cursor position.
+ * depending on it's position from the origin (ox, oy) and \a aPosiition..
  */
-void   Calcule_Coord_Extremite_45( int ox, int oy, int* fx, int* fy );
+void   Calcule_Coord_Extremite_45( const wxPoint& aPosition, int ox, int oy, int* fx, int* fy );
 
 
 /*****************/
diff --git a/pcbnew/zones_by_polygon.cpp b/pcbnew/zones_by_polygon.cpp
index 3ba5f3faad..e5e39158e4 100644
--- a/pcbnew/zones_by_polygon.cpp
+++ b/pcbnew/zones_by_polygon.cpp
@@ -750,8 +750,7 @@ static void Show_New_Edge_While_Move_Mouse( EDA_DRAW_PANEL* panel, wxDC* DC, boo
     {
         // calculate the new position as allowed
         wxPoint StartPoint = zone->GetCornerPosition( icorner - 1 );
-        Calcule_Coord_Extremite_45( StartPoint.x, StartPoint.y,
-            &c_pos.x, &c_pos.y );
+        Calcule_Coord_Extremite_45( c_pos, StartPoint.x, StartPoint.y, &c_pos.x, &c_pos.y );
     }
 
     zone->SetCornerPosition( icorner, c_pos );