From 9e387e48fc856a27cfd9a9d89f4a467d81ce34e4 Mon Sep 17 00:00:00 2001
From: Matthias Kuhn <matthias@opengis.ch>
Date: Thu, 23 Aug 2018 06:43:21 +0200
Subject: [PATCH] Make map tool snap to grid crs aware

---
 .../auto_generated/qgsmapmouseevent.sip.in    |  4 +++-
 src/gui/qgsmapmouseevent.cpp                  | 14 ++++++++-----
 src/gui/qgsmapmouseevent.h                    |  4 +++-
 src/gui/qgsmaptooladvanceddigitizing.cpp      | 21 +++++++++++++------
 4 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/python/gui/auto_generated/qgsmapmouseevent.sip.in b/python/gui/auto_generated/qgsmapmouseevent.sip.in
index a24366fd317..a2547417550 100644
--- a/python/gui/auto_generated/qgsmapmouseevent.sip.in
+++ b/python/gui/auto_generated/qgsmapmouseevent.sip.in
@@ -119,9 +119,11 @@ Alias to pos()
 :return: Mouse position in pixel coordinates
 %End
 
-    void snapToGrid( double precision );
+    void snapToGrid( double precision, const QgsCoordinateReferenceSystem &crs );
 %Docstring
 Snaps the mapPoint to a grid with the given ``precision``.
+The snapping will be done in the specified ``crs``. If this crs is
+different from the mapCanvas crs, it will add some overhead.
 
 .. versionadded:: 3.4
 %End
diff --git a/src/gui/qgsmapmouseevent.cpp b/src/gui/qgsmapmouseevent.cpp
index 9cf9cd9c016..baaa5ab6381 100644
--- a/src/gui/qgsmapmouseevent.cpp
+++ b/src/gui/qgsmapmouseevent.cpp
@@ -71,17 +71,21 @@ void QgsMapMouseEvent::setMapPoint( const QgsPointXY &point )
   mPixelPoint = mapToPixelCoordinates( point );
 }
 
-void QgsMapMouseEvent::snapToGrid( double precision )
+void QgsMapMouseEvent::snapToGrid( double precision, const QgsCoordinateReferenceSystem &crs )
 {
   if ( precision <= 0 )
     return;
 
-  mMapPoint.setX( std::round( mMapPoint.x() / precision ) * precision );
-  mMapPoint.setY( std::round( mMapPoint.y() / precision ) * precision );
+  QgsCoordinateTransform ct( mMapCanvas->mapSettings().destinationCrs(), crs, mMapCanvas->mapSettings().transformContext() );
 
-  // mSnapMatch = QgsPointLocator::Match( mSnapMatch.type(), mSnapMatch.layer(), mSnapMatch.featureId(), mSnapMatch.distance(), mMapPoint, mSnapMatch.vertexIndex(), mSnapMatch.edgePoints() );
+  QgsPointXY pt = ct.transform( mMapPoint );
 
-  setMapPoint( mMapPoint );
+  pt.setX( std::round( mMapPoint.x() / precision ) * precision );
+  pt.setY( std::round( mMapPoint.y() / precision ) * precision );
+
+  pt = ct.transform( pt, QgsCoordinateTransform::ReverseTransform );
+
+  setMapPoint( pt );
 }
 
 QPoint QgsMapMouseEvent::mapToPixelCoordinates( const QgsPointXY &point )
diff --git a/src/gui/qgsmapmouseevent.h b/src/gui/qgsmapmouseevent.h
index 0b89cec92a1..01d143d8ff5 100644
--- a/src/gui/qgsmapmouseevent.h
+++ b/src/gui/qgsmapmouseevent.h
@@ -128,10 +128,12 @@ class GUI_EXPORT QgsMapMouseEvent : public QMouseEvent
 
     /**
      * Snaps the mapPoint to a grid with the given \a precision.
+     * The snapping will be done in the specified \a crs. If this crs is
+     * different from the mapCanvas crs, it will add some overhead.
      *
      * \since QGIS 3.4
      */
-    void snapToGrid( double precision );
+    void snapToGrid( double precision, const QgsCoordinateReferenceSystem &crs );
 
   private:
 
diff --git a/src/gui/qgsmaptooladvanceddigitizing.cpp b/src/gui/qgsmaptooladvanceddigitizing.cpp
index 75c665acf6d..a1fd537f520 100644
--- a/src/gui/qgsmaptooladvanceddigitizing.cpp
+++ b/src/gui/qgsmaptooladvanceddigitizing.cpp
@@ -39,8 +39,11 @@ void QgsMapToolAdvancedDigitizing::canvasPressEvent( QgsMapMouseEvent *e )
     e->snapPoint();
   }
 
-  if ( currentVectorLayer() )
-    e->snapToGrid( currentVectorLayer()->geometryOptions().geometryPrecision );
+  QgsVectorLayer *layer = currentVectorLayer();
+  if ( layer )
+  {
+    e->snapToGrid( layer->geometryOptions().geometryPrecision, layer->crs() );
+  }
 
   cadCanvasPressEvent( e );
 }
@@ -76,8 +79,11 @@ void QgsMapToolAdvancedDigitizing::canvasReleaseEvent( QgsMapMouseEvent *e )
     e->snapPoint();
   }
 
-  if ( currentVectorLayer() )
-    e->snapToGrid( currentVectorLayer()->geometryOptions().geometryPrecision );
+  QgsVectorLayer *layer = currentVectorLayer();
+  if ( layer )
+  {
+    e->snapToGrid( layer->geometryOptions().geometryPrecision, layer->crs() );
+  }
 
   cadCanvasReleaseEvent( e );
 }
@@ -98,8 +104,11 @@ void QgsMapToolAdvancedDigitizing::canvasMoveEvent( QgsMapMouseEvent *e )
     e->snapPoint();
   }
 
-  if ( currentVectorLayer() )
-    e->snapToGrid( currentVectorLayer()->geometryOptions().geometryPrecision );
+  QgsVectorLayer *layer = currentVectorLayer();
+  if ( layer )
+  {
+    e->snapToGrid( layer->geometryOptions().geometryPrecision, layer->crs() );
+  }
 
   cadCanvasMoveEvent( e );
 }