[bugfix] Transfer focus to canvas when selecting transparency

This is an attempt to fix #17845 Setting Raster Transparency
using "Add values from display" doesn't work

Fixes #17845

src/app/qgisapp.cpp

@@ -12629,9 +12629,21 @@ void QgisApp::showLayerProperties( QgsMapLayer *ml )
 #else
     QgsRasterLayerProperties *rlp = new QgsRasterLayerProperties( ml, mMapCanvas, this );
 #endif
-
-    rlp->exec();
-    delete rlp; // delete since dialog cannot be reused without updating code
+    // Cannot use exec here due to raster transparency map tool:
+    // in order to pass focus to the canvas, the dialog needs to
+    // be hidden and shown in non-modal mode.
+    rlp->setModal( true );
+    rlp->show();
+    // Delete (later, for safety) since dialog cannot be reused without
+    // updating code
+    connect( rlp, &QgsRasterLayerProperties::accepted, [ rlp ]
+    {
+      rlp->deleteLater();
+    } );
+    connect( rlp, &QgsRasterLayerProperties::rejected, [ rlp ]
+    {
+      rlp->deleteLater();
+    } );
   }
   else if ( ml->type() == QgsMapLayer::VectorLayer ) // VECTOR
   {

src/app/qgsrasterlayerproperties.cpp

@@ -176,11 +176,10 @@ QgsRasterLayerProperties::QgsRasterLayerProperties( QgsMapLayer *lyr, QgsMapCanv
   pbnImportTransparentPixelValues->setIcon( QgsApplication::getThemeIcon( QStringLiteral( "/mActionFileOpen.svg" ) ) );
   pbnExportTransparentPixelValues->setIcon( QgsApplication::getThemeIcon( QStringLiteral( "/mActionFileSave.svg" ) ) );
 
-  mPixelSelectorTool = nullptr;
   if ( mMapCanvas )
   {
-    mPixelSelectorTool = new QgsMapToolEmitPoint( canvas );
-    connect( mPixelSelectorTool, &QgsMapToolEmitPoint::canvasClicked, this, &QgsRasterLayerProperties::pixelSelected );
+    mPixelSelectorTool = qgis::make_unique<QgsMapToolEmitPoint>( canvas );
+    connect( mPixelSelectorTool.get(), &QgsMapToolEmitPoint::canvasClicked, this, &QgsRasterLayerProperties::pixelSelected );
   }
   else
   {
@@ -455,10 +454,6 @@ QgsRasterLayerProperties::QgsRasterLayerProperties( QgsMapLayer *lyr, QgsMapCanv
 
 QgsRasterLayerProperties::~QgsRasterLayerProperties()
 {
-  if ( mPixelSelectorTool )
-  {
-    delete mPixelSelectorTool;
-  }
 }
 
 void QgsRasterLayerProperties::setupTransparencyTable( int nBands )
@@ -1197,16 +1192,18 @@ void QgsRasterLayerProperties::pbnAddValuesFromDisplay_clicked()
 {
   if ( mMapCanvas && mPixelSelectorTool )
   {
-    mMapCanvas->setMapTool( mPixelSelectorTool );
     //Need to work around the modality of the dialog but can not just hide() it.
+    // According to Qt5 docs, to change modality the dialog needs to be hidden
+    // and shown it again.
+    hide();
     setModal( false );
-
     showMinimized();
 
-    //Q_ASSERT( parentWidget()->parentWidget() );
-    parentWidget()->activateWindow();
-    parentWidget()->raise();
-    //lower();
+    // Transfer focus to the canvas to use the selector tool
+    mMapCanvas->window()->raise();
+    mMapCanvas->window()->activateWindow();
+    mMapCanvas->window()->setFocus();
+    mMapCanvas->setMapTool( mPixelSelectorTool.get() );
   }
 }
 
@@ -1630,8 +1627,9 @@ void QgsRasterLayerProperties::pbnRemoveSelectedRow_clicked()
   }
 }
 
-void QgsRasterLayerProperties::pixelSelected( const QgsPointXY &canvasPoint )
+void QgsRasterLayerProperties::pixelSelected( const QgsPointXY &canvasPoint, const Qt::MouseButton &btn )
 {
+  Q_UNUSED( btn );
   QgsRasterRenderer *renderer = mRendererWidget->renderer();
   if ( !renderer )
   {
@@ -1645,7 +1643,7 @@ void QgsRasterLayerProperties::pixelSelected( const QgsPointXY &canvasPoint )
   //Get the pixel values and add a new entry to the transparency table
   if ( mMapCanvas && mPixelSelectorTool )
   {
-    mMapCanvas->unsetMapTool( mPixelSelectorTool );
+    mMapCanvas->unsetMapTool( mPixelSelectorTool.get() );
 
     const QgsMapSettings &ms = mMapCanvas->mapSettings();
     QgsPointXY myPoint = ms.mapToLayerCoordinates( mRasterLayer, canvasPoint );

src/app/qgsrasterlayerproperties.h

@@ -26,13 +26,13 @@
 #include "qgsguiutils.h"
 #include "qgshelp.h"
 #include "qgsmaplayerstylemanager.h"
+#include "qgsmaptoolemitpoint.h"
 #include "qgis_app.h"
 
 class QgsPointXY;
 class QgsMapLayer;
 class QgsMapCanvas;
 class QgsRasterLayer;
-class QgsMapToolEmitPoint;
 class QgsMetadataWidget;
 class QgsRasterRenderer;
 class QgsRasterRendererWidget;
@@ -91,7 +91,7 @@ class APP_EXPORT QgsRasterLayerProperties : public QgsOptionsDialogBase, private
      */
     //void on_btnResetNull_clicked();
 
-    void pixelSelected( const QgsPointXY & );
+    void pixelSelected( const QgsPointXY &, const Qt::MouseButton & );
 
   private slots:
     void mRenderTypeComboBox_currentIndexChanged( int index );
@@ -206,7 +206,7 @@ class APP_EXPORT QgsRasterLayerProperties : public QgsOptionsDialogBase, private
     qreal mGradientWidth;
 
     QgsMapCanvas *mMapCanvas = nullptr;
-    QgsMapToolEmitPoint *mPixelSelectorTool = nullptr;
+    std::unique_ptr<QgsMapToolEmitPoint> mPixelSelectorTool = nullptr;
 
     QgsRasterHistogramWidget *mHistogramWidget = nullptr;