[FEATURE] Allow web map style shift-drag zoom

When certain map tools are active, you can hold down shift
and drag a rectangle on the map to zoom to that area. This
is enabled for the map tools which are not selection tools
(since they use shift for adding to selection), and edit
tools.

Gracias a Girona!

Author: nyalldawson

python/gui/qgsmaptool.sip

@@ -38,6 +38,7 @@ class QgsMapTool : QObject
                                If it does, the tool can be operated once and then a previous map
                                tool automatically restored. */
       EditTool, /*!< Map tool is an edit tool, which can only be used when layer is editable*/
+      AllowZoomRect, /*!< Allow zooming by rectangle (by holding shift and dragging) while the tool is active*/
     };
     typedef QFlags<QgsMapTool::Flag> Flags;
 
@@ -183,3 +184,6 @@ class QgsMapTool : QObject
 
 
 };
+
+
+QFlags<QgsMapTool::Flag> operator|(QgsMapTool::Flag f1, QFlags<QgsMapTool::Flag> f2);

python/gui/qgsmaptoolemitpoint.sip

@@ -9,6 +9,8 @@ class QgsMapToolEmitPoint : QgsMapTool
     //! constructor
     QgsMapToolEmitPoint( QgsMapCanvas* canvas );
 
+    virtual Flags flags() const;
+
     //! Overridden mouse move event
     virtual void canvasMoveEvent( QgsMapMouseEvent * e );
 

python/gui/qgsmaptoolidentify.sip

@@ -47,6 +47,8 @@ class QgsMapToolIdentify : QgsMapTool
 
     virtual ~QgsMapToolIdentify();
 
+    virtual Flags flags() const;
+
     //! Overridden mouse move event
     virtual void canvasMoveEvent( QgsMapMouseEvent * e );
 

src/app/qgsmaptoolfeatureaction.h

@@ -36,6 +36,8 @@ class APP_EXPORT QgsMapToolFeatureAction : public QgsMapTool
 
     ~QgsMapToolFeatureAction();
 
+    virtual Flags flags() const override { return QgsMapTool::AllowZoomRect; }
+
     //! Overridden mouse move event
     virtual void canvasMoveEvent( QgsMapMouseEvent* e ) override;
 

src/app/qgsmaptoolmeasureangle.h

@@ -31,7 +31,9 @@ class APP_EXPORT QgsMapToolMeasureAngle: public QgsMapTool
     QgsMapToolMeasureAngle( QgsMapCanvas* canvas );
     ~QgsMapToolMeasureAngle();
 
-    //! Mouse move event for overridingqgs
+    virtual Flags flags() const override { return QgsMapTool::AllowZoomRect; }
+
+    //! Mouse move event for overriding
     void canvasMoveEvent( QgsMapMouseEvent* e ) override;
 
     //! Mouse release event for overriding

src/app/qgsmaptoolpointsymbol.h

@@ -34,7 +34,7 @@ class APP_EXPORT QgsMapToolPointSymbol: public QgsMapToolEdit
   public:
     QgsMapToolPointSymbol( QgsMapCanvas* canvas );
 
-    virtual Flags flags() const { return QgsMapTool::EditTool; }
+    virtual Flags flags() const override { return QgsMapTool::EditTool; }
 
     void canvasPressEvent( QgsMapMouseEvent* e ) override;
 

src/app/qgsmeasuretool.h

@@ -36,6 +36,8 @@ class APP_EXPORT QgsMeasureTool : public QgsMapTool
 
     ~QgsMeasureTool();
 
+    virtual Flags flags() const override { return QgsMapTool::AllowZoomRect; }
+
     //! returns whether measuring distance or area
     bool measureArea() { return mMeasureArea; }
 

src/gui/qgsmapcanvas.cpp

@@ -62,6 +62,7 @@ email                : sherman at mrcc.com
 #include "qgsproject.h"
 #include "qgsrubberband.h"
 #include "qgsvectorlayer.h"
+#include "qgscursors.h"
 #include <math.h>
 
 
@@ -212,6 +213,7 @@ QgsMapCanvas::QgsMapCanvas( QWidget * parent, const char *name )
     , mSnappingUtils( nullptr )
     , mScaleLocked( false )
     , mExpressionContextScope( tr( "Map Canvas" ) )
+    , mZoomDragging( false )
 {
   setObjectName( name );
   mScene = new QGraphicsScene();
@@ -273,6 +275,9 @@ QgsMapCanvas::QgsMapCanvas( QWidget * parent, const char *name )
   mPreviewEffect = new QgsPreviewEffect( this );
   viewport()->setGraphicsEffect( mPreviewEffect );
 
+  QPixmap zoomPixmap = QPixmap(( const char ** )( zoom_in ) );
+  mZoomCursor = QCursor( zoomPixmap, 7, 7 );
+
   setInteractive( false );
 
   refresh();
@@ -1342,6 +1347,50 @@ void QgsMapCanvas::mouseDoubleClickEvent( QMouseEvent* e )
 }// mouseDoubleClickEvent
 
 
+void QgsMapCanvas::beginZoomRect( QPoint pos )
+{
+  mZoomRect.setRect( 0, 0, 0, 0 );
+  QApplication::setOverrideCursor( mZoomCursor );
+  mZoomDragging = true;
+  mZoomRubberBand.reset( new QgsRubberBand( this, QGis::Polygon ) );
+  QColor color( Qt::blue );
+  color.setAlpha( 63 );
+  mZoomRubberBand->setColor( color );
+  mZoomRect.setTopLeft( pos );
+}
+
+void QgsMapCanvas::endZoomRect( QPoint pos )
+{
+  mZoomDragging = false;
+  mZoomRubberBand.reset( nullptr );
+  QApplication::restoreOverrideCursor();
+
+  // store the rectangle
+  mZoomRect.setRight( pos.x() );
+  mZoomRect.setBottom( pos.y() );
+
+  if ( mZoomRect.width() < 5 && mZoomRect.height() < 5 )
+  {
+    //probably a mistake - would result in huge zoom!
+    return;
+  }
+
+  //account for bottom right -> top left dragging
+  mZoomRect = mZoomRect.normalized();
+
+  // set center and zoom
+  const QSize& zoomRectSize = mZoomRect.size();
+  const QSize& canvasSize = mSettings.outputSize();
+  double sfx = ( double )zoomRectSize.width() / canvasSize.width();
+  double sfy = ( double )zoomRectSize.height() / canvasSize.height();
+  double sf = qMax( sfx, sfy );
+
+  QgsPoint c = mSettings.mapToPixel().toMapCoordinates( mZoomRect.center() );
+
+  zoomByFactor( sf, &c );
+  refresh();
+}
+
 void QgsMapCanvas::mousePressEvent( QMouseEvent* e )
 {
   //use middle mouse button for panning, map tools won't receive any events in that case
@@ -1352,12 +1401,20 @@ void QgsMapCanvas::mousePressEvent( QMouseEvent* e )
   }
   else
   {
-
     // call handler of current map tool
     if ( mMapTool )
     {
-      QScopedPointer<QgsMapMouseEvent> me( new QgsMapMouseEvent( this, e ) );
-      mMapTool->canvasPressEvent( me.data() );
+      if ( mMapTool->flags() & QgsMapTool::AllowZoomRect && e->button() == Qt::LeftButton
+           && e->modifiers() & Qt::ShiftModifier )
+      {
+        beginZoomRect( e->pos() );
+        return;
+      }
+      else
+      {
+        QScopedPointer<QgsMapMouseEvent> me( new QgsMapMouseEvent( this, e ) );
+        mMapTool->canvasPressEvent( me.data() );
+      }
     }
   }
 
@@ -1382,6 +1439,12 @@ void QgsMapCanvas::mouseReleaseEvent( QMouseEvent* e )
   }
   else
   {
+    if ( mZoomDragging && e->button() == Qt::LeftButton )
+    {
+      endZoomRect( e->pos() );
+      return;
+    }
+
     // call handler of current map tool
     if ( mMapTool )
     {
@@ -1572,6 +1635,12 @@ void QgsMapCanvas::mouseMoveEvent( QMouseEvent * e )
   {
     panAction( e );
   }
+  else if ( mZoomDragging )
+  {
+    mZoomRect.setBottomRight( e->pos() );
+    mZoomRubberBand->setToCanvasRectangle( mZoomRect );
+    mZoomRubberBand->show();
+  }
   else
   {
     // call handler of current map tool

src/gui/qgsmapcanvas.h

@@ -65,6 +65,7 @@ class QgsMapCanvasMap;
 class QgsMapOverviewCanvas;
 class QgsMapTool;
 class QgsSnappingUtils;
+class QgsRubberBand;
 
 /** \ingroup gui
   * A class that stores visibility and presence in overview flags together
@@ -785,10 +786,33 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
 
     QgsExpressionContextScope mExpressionContextScope;
 
+    //! Stores zoom rect
+    QRect mZoomRect;
+
+    //! Flag to indicate a zoom by rectangle operation is taking place
+    bool mZoomDragging;
+
+    //! Zoom by rectangle rubber band
+    QScopedPointer< QgsRubberBand > mZoomRubberBand;
+
+    QCursor mZoomCursor;
+
     //! Force a resize of the map canvas item
     //! @note added in 2.16
     void updateMapSize();
 
+    /** Starts zooming via rectangle
+     * @param pos start position for rectangle
+     * @note added in QGIS 2.16
+     */
+    void beginZoomRect( QPoint pos );
+
+    /** Ends zooming via rectangle
+     * @param pos end position for rectangle
+     * @note added in QGIS 2.16
+     */
+    void endZoomRect( QPoint pos );
+
     friend class TestQgsMapCanvas;
 
 }; // class QgsMapCanvas

src/gui/qgsmaptool.h

@@ -62,6 +62,7 @@ class GUI_EXPORT QgsMapTool : public QObject
                                If it does, the tool can be operated once and then a previous map
                                tool automatically restored. */
       EditTool = 1 << 2, /*!< Map tool is an edit tool, which can only be used when layer is editable*/
+      AllowZoomRect = 1 << 3, /*!< Allow zooming by rectangle (by holding shift and dragging) while the tool is active*/
     };
     Q_DECLARE_FLAGS( Flags, Flag )
 
@@ -224,6 +225,9 @@ class GUI_EXPORT QgsMapTool : public QObject
 
     //! translated name of the map tool
     QString mToolName;
+
 };
 
+Q_DECLARE_OPERATORS_FOR_FLAGS( QgsMapTool::Flags )
+
 #endif

src/gui/qgsmaptooledit.h

@@ -33,7 +33,7 @@ class GUI_EXPORT QgsMapToolEdit: public QgsMapTool
     QgsMapToolEdit( QgsMapCanvas* canvas );
     virtual ~QgsMapToolEdit();
 
-    virtual Flags flags() const { return QgsMapTool::EditTool; }
+    virtual Flags flags() const override { return QgsMapTool::EditTool; }
 
   protected:
 

src/gui/qgsmaptoolemitpoint.h

@@ -34,6 +34,8 @@ class GUI_EXPORT QgsMapToolEmitPoint : public QgsMapTool
     //! constructor
     QgsMapToolEmitPoint( QgsMapCanvas* canvas );
 
+    virtual Flags flags() const override { return QgsMapTool::AllowZoomRect; }
+
     //! Overridden mouse move event
     virtual void canvasMoveEvent( QgsMapMouseEvent* e ) override;
 

src/gui/qgsmaptoolidentify.h

@@ -92,6 +92,8 @@ class GUI_EXPORT QgsMapToolIdentify : public QgsMapTool
 
     virtual ~QgsMapToolIdentify();
 
+    virtual Flags flags() const override { return QgsMapTool::AllowZoomRect; }
+
     //! Overridden mouse move event
     virtual void canvasMoveEvent( QgsMapMouseEvent* e ) override;
 

src/gui/qgsmaptoolpan.h

@@ -32,7 +32,7 @@ class GUI_EXPORT QgsMapToolPan : public QgsMapTool
     //! constructor
     QgsMapToolPan( QgsMapCanvas* canvas );
 
-    virtual Flags flags() const { return QgsMapTool::Transient; }
+    virtual Flags flags() const override { return QgsMapTool::Transient | QgsMapTool::AllowZoomRect; }
 
     //! Mouse press event
     virtual void canvasPressEvent( QgsMapMouseEvent* e ) override;

src/gui/qgsmaptoolzoom.h

@@ -35,7 +35,7 @@ class GUI_EXPORT QgsMapToolZoom : public QgsMapTool
 
     ~QgsMapToolZoom();
 
-    virtual Flags flags() const { return QgsMapTool::Transient; }
+    virtual Flags flags() const override { return QgsMapTool::Transient; }
 
     //! Overridden mouse move event
     virtual void canvasMoveEvent( QgsMapMouseEvent* e ) override;