Add QgsMapCanvas::setZoomResolutions

qgis · Jan 17, 2020 · 8410ea7 · 8410ea7
1 parent c658159
commit 8410ea7
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Showing 4 changed files with 111 additions and 4 deletions.
diff --git a/python/gui/auto_generated/qgsmapcanvas.sip.in b/python/gui/auto_generated/qgsmapcanvas.sip.in
@@ -841,6 +841,25 @@ Zoom out with fixed factor
 Zoom to the extent of the selected features of provided (vector) layer.
 
 :param layer: optionally specify different than current layer
+%End
+
+    void setZoomResolutions( const QList<double> &resolutions );
+%Docstring
+Set a list of resolutions (map units per pixel) to which to "snap to" when zooming the map
+
+:param resolutions: A list of resolutions
+
+.. versionadded:: 3.12
+%End
+
+    const QList<double> &zoomResolutions() const;
+%Docstring
+
+:return: List of resolutions to which to "snap to" when zooming the map
+
+.. seealso:: :py:func:`setZoomResolutions`
+
+.. versionadded:: 3.12
 %End
 
   signals:

diff --git a/src/gui/qgsmapcanvas.cpp b/src/gui/qgsmapcanvas.cpp
@@ -1639,7 +1639,7 @@ void QgsMapCanvas::wheelEvent( QWheelEvent *e )
     return;
   }
 
-  double zoomFactor = mWheelZoomFactor;
+  double zoomFactor = e->angleDelta().y() > 0 ? 1. / zoomInFactor() : zoomOutFactor();
 
   // "Normal" mouse have an angle delta of 120, precision mouses provide data faster, in smaller steps
   zoomFactor = 1.0 + ( zoomFactor - 1.0 ) / 120.0 * std::fabs( e->angleDelta().y() );
@@ -1670,13 +1670,13 @@ void QgsMapCanvas::setWheelFactor( double factor )
 void QgsMapCanvas::zoomIn()
 {
   // magnification is alreday handled in zoomByFactor
-  zoomByFactor( 1 / mWheelZoomFactor );
+  zoomByFactor( zoomInFactor() );
 }
 
 void QgsMapCanvas::zoomOut()
 {
   // magnification is alreday handled in zoomByFactor
-  zoomByFactor( mWheelZoomFactor );
+  zoomByFactor( zoomOutFactor() );
 }
 
 void QgsMapCanvas::zoomScale( double newScale )
@@ -1686,7 +1686,7 @@ void QgsMapCanvas::zoomScale( double newScale )
 
 void QgsMapCanvas::zoomWithCenter( int x, int y, bool zoomIn )
 {
-  double scaleFactor = ( zoomIn ? 1 / mWheelZoomFactor : mWheelZoomFactor );
+  double scaleFactor = ( zoomIn ? zoomInFactor() : zoomOutFactor() );
 
   if ( mScaleLocked )
   {
@@ -2522,3 +2522,50 @@ bool QgsMapCanvas::panOperationInProgress()
 
   return false;
 }
+
+int QgsMapCanvas::nextZoomLevel( const QList<double> &resolutions, bool zoomIn ) const
+{
+  int resolutionLevel = -1;
+  double currentResolution = mapUnitsPerPixel();
+
+  for ( int i = 0, n = resolutions.size(); i < n; ++i )
+  {
+    if ( qgsDoubleNear( resolutions[i], currentResolution, 0.0001 ) )
+    {
+      resolutionLevel = zoomIn ? ( i - 1 ) : ( i + 1 );
+      break;
+    }
+    else if ( currentResolution <= resolutions[i] )
+    {
+      resolutionLevel = zoomIn ? ( i - 1 ) : i;
+      break;
+    }
+  }
+  return ( resolutionLevel < 0 || resolutionLevel >= resolutions.size() ) ? -1 : resolutionLevel;
+}
+
+double QgsMapCanvas::zoomInFactor() const
+{
+  if ( !mZoomResolutions.isEmpty() )
+  {
+    int zoomLevel = nextZoomLevel( mZoomResolutions, true );
+    if ( zoomLevel != -1 )
+    {
+      return mZoomResolutions.at( zoomLevel ) / mapUnitsPerPixel();
+    }
+  }
+  return 1 / mWheelZoomFactor;
+}
+
+double QgsMapCanvas::zoomOutFactor() const
+{
+  if ( !mZoomResolutions.isEmpty() )
+  {
+    int zoomLevel = nextZoomLevel( mZoomResolutions, false );
+    if ( zoomLevel != -1 )
+    {
+      return mZoomResolutions.at( zoomLevel ) / mapUnitsPerPixel();
+    }
+  }
+  return mWheelZoomFactor;
+}
diff --git a/src/gui/qgsmapcanvas.h b/src/gui/qgsmapcanvas.h
@@ -751,6 +751,20 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
      */
     void zoomToSelected( QgsVectorLayer *layer = nullptr );
 
+    /**
+     * Set a list of resolutions (map units per pixel) to which to "snap to" when zooming the map
+     * \param resolutions A list of resolutions
+     * \since QGIS 3.12
+     */
+    void setZoomResolutions( const QList<double> &resolutions ) { mZoomResolutions = resolutions; }
+
+    /**
+     * \returns List of resolutions to which to "snap to" when zooming the map
+     * \see setZoomResolutions()
+     * \since QGIS 3.12
+     */
+    const QList<double> &zoomResolutions() const { return mZoomResolutions; }
+
   private slots:
     //! called when current maptool is destroyed
     void mapToolDestroyed();
@@ -1055,6 +1069,7 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
     QVector<QPointer<QgsCustomDropHandler >> mDropHandlers;
 
     QgsDistanceArea mDa;
+    QList<double> mZoomResolutions;
 
     /**
      * Returns the last cursor position on the canvas in geographical coordinates
@@ -1102,6 +1117,10 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
      */
     bool panOperationInProgress();
 
+    int nextZoomLevel( const QList<double> &resolutions, bool zoomIn = true ) const;
+    double zoomInFactor() const;
+    double zoomOutFactor() const;
+
     friend class TestQgsMapCanvas;
 
 }; // class QgsMapCanvas

diff --git a/tests/src/gui/testqgsmapcanvas.cpp b/tests/src/gui/testqgsmapcanvas.cpp
@@ -61,6 +61,7 @@ class TestQgsMapCanvas : public QObject
     void testZoomByWheel();
     void testShiftZoom();
     void testDragDrop();
+    void testZoomResolutions();
 
   private:
     QgsMapCanvas *mCanvas = nullptr;
@@ -514,5 +515,26 @@ void TestQgsMapCanvas::testDragDrop()
   QVERIFY( dropEvent->isAccepted() );
 }
 
+void TestQgsMapCanvas::testZoomResolutions()
+{
+  mCanvas->setExtent( QgsRectangle( 0, 0, 10, 10 ) );
+  double resolution = mCanvas->mapSettings().mapUnitsPerPixel();
+
+  double nextResolution = qCeil( resolution ) + 1;
+  QList<double> resolutions = QList<double>() << nextResolution << ( 2.5 * nextResolution ) << ( 3.6 * nextResolution ) << ( 4.7 * nextResolution );
+  mCanvas->setZoomResolutions( resolutions );
+
+  mCanvas->zoomOut();
+  QGSCOMPARENEAR( mCanvas->mapSettings().mapUnitsPerPixel(), resolutions[0], 0.0001 );
+
+  mCanvas->zoomOut();
+  QGSCOMPARENEAR( mCanvas->mapSettings().mapUnitsPerPixel(), resolutions[1], 0.0001 );
+
+  mCanvas->zoomIn();
+  QGSCOMPARENEAR( mCanvas->mapSettings().mapUnitsPerPixel(), resolutions[0], 0.0001 );
+
+  QCOMPARE( mCanvas->zoomResolutions(), resolutions );
+}
+
 QGSTEST_MAIN( TestQgsMapCanvas )
 #include "testqgsmapcanvas.moc"