Fixes #17845 tested on Linux KDE and Win 10

src/app/qgisapp.cpp

@@ -12568,7 +12568,7 @@ void QgisApp::readProject( const QDomDocument &doc )
   }
 }
 
-void QgisApp::showLayerProperties( QgsMapLayer *ml )
+void QgisApp::showLayerProperties( QgsMapLayer *mapLayer )
 {
   /*
   TODO: Consider reusing the property dialogs again.
@@ -12579,15 +12579,15 @@ void QgisApp::showLayerProperties( QgsMapLayer *ml )
   a separate copy of the dialog pointer needs to be stored with each layer.
   */
 
-  if ( !ml )
+  if ( !mapLayer )
     return;
 
-  if ( !QgsProject::instance()->layerIsEmbedded( ml->id() ).isEmpty() )
+  if ( !QgsProject::instance()->layerIsEmbedded( mapLayer->id() ).isEmpty() )
   {
     return; //don't show properties of embedded layers
   }
 
-  if ( ml->type() == QgsMapLayer::RasterLayer )
+  if ( mapLayer->type() == QgsMapLayer::RasterLayer )
   {
 #if 0 // See note above about reusing this
     QgsRasterLayerProperties *rlp = nullptr;
@@ -12601,27 +12601,27 @@ void QgisApp::showLayerProperties( QgsMapLayer *ml )
       // handled by rendererChanged() connect( rlp, SIGNAL( refreshLegend( QString, bool ) ), mLayerTreeView, SLOT( refreshLayerSymbology( QString ) ) );
     }
 #else
-    QgsRasterLayerProperties *rlp = new QgsRasterLayerProperties( ml, mMapCanvas, this );
+    QgsRasterLayerProperties *rasterLayerPropertiesDialog = new QgsRasterLayerProperties( mapLayer, mMapCanvas, this );
 #endif
     // 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();
+    rasterLayerPropertiesDialog->setModal( true );
+    rasterLayerPropertiesDialog->show();
     // Delete (later, for safety) since dialog cannot be reused without
     // updating code
-    connect( rlp, &QgsRasterLayerProperties::accepted, [ rlp ]
+    connect( rasterLayerPropertiesDialog, &QgsRasterLayerProperties::accepted, [ rasterLayerPropertiesDialog ]
     {
-      rlp->deleteLater();
+      rasterLayerPropertiesDialog->deleteLater();
     } );
-    connect( rlp, &QgsRasterLayerProperties::rejected, [ rlp ]
+    connect( rasterLayerPropertiesDialog, &QgsRasterLayerProperties::rejected, [ rasterLayerPropertiesDialog ]
     {
-      rlp->deleteLater();
+      rasterLayerPropertiesDialog->deleteLater();
     } );
   }
-  else if ( ml->type() == QgsMapLayer::VectorLayer ) // VECTOR
+  else if ( mapLayer->type() == QgsMapLayer::VectorLayer ) // VECTOR
   {
-    QgsVectorLayer *vlayer = qobject_cast<QgsVectorLayer *>( ml );
+    QgsVectorLayer *vlayer = qobject_cast<QgsVectorLayer *>( mapLayer );
 
 #if 0 // See note above about reusing this
     QgsVectorLayerProperties *vlp = nullptr;
@@ -12635,26 +12635,26 @@ void QgisApp::showLayerProperties( QgsMapLayer *ml )
       // handled by rendererChanged() connect( vlp, SIGNAL( refreshLegend( QString ) ), mLayerTreeView, SLOT( refreshLayerSymbology( QString ) ) );
     }
 #else
-    QgsVectorLayerProperties *vlp = new QgsVectorLayerProperties( vlayer, this );
+    QgsVectorLayerProperties *vectorLayerPropertiesDialog = new QgsVectorLayerProperties( vlayer, this );
 #endif
     Q_FOREACH ( QgsMapLayerConfigWidgetFactory *factory, mMapLayerPanelFactories )
     {
-      vlp->addPropertiesPageFactory( factory );
+      vectorLayerPropertiesDialog->addPropertiesPageFactory( factory );
     }
 
     mMapStyleWidget->blockUpdates( true );
-    if ( vlp->exec() )
+    if ( vectorLayerPropertiesDialog->exec() )
     {
-      activateDeactivateLayerRelatedActions( ml );
+      activateDeactivateLayerRelatedActions( mapLayer );
       mMapStyleWidget->updateCurrentWidgetLayer();
     }
     mMapStyleWidget->blockUpdates( false );
 
-    delete vlp; // delete since dialog cannot be reused without updating code
+    delete vectorLayerPropertiesDialog; // delete since dialog cannot be reused without updating code
   }
-  else if ( ml->type() == QgsMapLayer::PluginLayer )
+  else if ( mapLayer->type() == QgsMapLayer::PluginLayer )
   {
-    QgsPluginLayer *pl = qobject_cast<QgsPluginLayer *>( ml );
+    QgsPluginLayer *pl = qobject_cast<QgsPluginLayer *>( mapLayer );
     if ( !pl )
       return;
 

src/app/qgisapp.h

@@ -603,7 +603,7 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     QgsLocatorWidget *locatorWidget() { return mLocatorWidget; }
 
     //! show layer properties
-    void showLayerProperties( QgsMapLayer *ml );
+    void showLayerProperties( QgsMapLayer *mapLayer );
 
     //! returns pointer to map legend
     QgsLayerTreeView *layerTreeView();

src/app/qgsrasterlayerproperties.cpp

@@ -180,6 +180,7 @@ QgsRasterLayerProperties::QgsRasterLayerProperties( QgsMapLayer *lyr, QgsMapCanv
   {
     mPixelSelectorTool = qgis::make_unique<QgsMapToolEmitPoint>( canvas );
     connect( mPixelSelectorTool.get(), &QgsMapToolEmitPoint::canvasClicked, this, &QgsRasterLayerProperties::pixelSelected );
+    connect( mPixelSelectorTool.get(), &QgsMapToolEmitPoint::deactivated, this, &QgsRasterLayerProperties::restoreWindowModality );
   }
   else
   {
@@ -1194,16 +1195,16 @@ void QgsRasterLayerProperties::pbnAddValuesFromDisplay_clicked()
   {
     //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.
+    // and shown again.
     hide();
     setModal( false );
-    showMinimized();
 
     // Transfer focus to the canvas to use the selector tool
     mMapCanvas->window()->raise();
     mMapCanvas->window()->activateWindow();
     mMapCanvas->window()->setFocus();
     mMapCanvas->setMapTool( mPixelSelectorTool.get() );
+
   }
 }
 
@@ -1636,10 +1637,6 @@ void QgsRasterLayerProperties::pixelSelected( const QgsPointXY &canvasPoint, con
     return;
   }
 
-  raise();
-  setModal( true );
-  activateWindow();
-
   //Get the pixel values and add a new entry to the transparency table
   if ( mMapCanvas && mPixelSelectorTool )
   {
@@ -1872,6 +1869,15 @@ void QgsRasterLayerProperties::saveStyleAs_clicked()
     QMessageBox::information( this, tr( "Saved Style" ), message );
 }
 
+void QgsRasterLayerProperties::restoreWindowModality()
+{
+  hide();
+  setModal( true );
+  show();
+  raise();
+  activateWindow();
+}
+
 //
 //
 // Next four methods for saving and restoring QMD metadata

src/app/qgsrasterlayerproperties.h

@@ -103,6 +103,9 @@ class APP_EXPORT QgsRasterLayerProperties : public QgsOptionsDialogBase, private
     void loadStyle_clicked();
     //! Save a style when appriate button is pressed.
     void saveStyleAs_clicked();
+    //! Restore dialog modality and focus, usually after a pixel clicked to pick transparency color
+    void restoreWindowModality();
+
 
     //! Load a saved metadata file.
     void loadMetadata();