[FEATURE] Flash features in canvas

This adds:
- API call to QgsMapCanvas to flash a set of features
- A right click menu option in the attribute table to flash
the clicked feature
- An option in the Search by Form dialog to flash matching
features

When triggered, the features flash allowing easy identification
without having to alter the current selection or map extent

python/gui/qgsattributeform.sip

@@ -163,6 +163,12 @@ class QgsAttributeForm : QWidget
 %Docstring
  Emitted when the user chooses to zoom to a filtered set of features.
 .. versionadded:: 3.0
+%End
+
+    void flashFeatures( const QString &filter );
+%Docstring
+ Emitted when the user chooses to flash a filtered set of features.
+.. versionadded:: 3.0
 %End
 
   public slots:

python/gui/qgsmapcanvas.sip

@@ -232,6 +232,19 @@ Zoom to the next extent (view)
     void panToSelected( QgsVectorLayer *layer = 0 );
 %Docstring
 Pan to the selected features of current (vector) layer keeping same extent.
+%End
+
+    void flashFeatureIds( QgsVectorLayer *layer, const QgsFeatureIds &ids,
+                          const QColor &startColor = QColor( 255, 0, 0, 255 ), const QColor &endColor = QColor( 255, 0, 0, 0 ),
+                          int flashes = 3, int duration = 500 );
+%Docstring
+ Causes a set of features with matching ``ids`` from a vector ``layer`` to flash
+ within the canvas.
+
+ The ``startColor`` and ``endColor`` can be specified, along with the number of
+ ``flashes`` and ``duration`` of each flash (in milliseconds).
+
+.. versionadded:: 3.0
 %End
 
     void setMapTool( QgsMapTool *mapTool );

src/app/qgsselectbyformdialog.cpp

@@ -63,6 +63,7 @@ void QgsSelectByFormDialog::setMapCanvas( QgsMapCanvas *canvas )
 {
   mMapCanvas = canvas;
   connect( mForm, &QgsAttributeForm::zoomToFeatures, this, &QgsSelectByFormDialog::zoomToFeatures );
+  connect( mForm, &QgsAttributeForm::flashFeatures, this, &QgsSelectByFormDialog::flashFeatures );
 }
 
 void QgsSelectByFormDialog::zoomToFeatures( const QString &filter )
@@ -112,3 +113,35 @@ void QgsSelectByFormDialog::zoomToFeatures( const QString &filter )
                               timeout );
   }
 }
+
+void QgsSelectByFormDialog::flashFeatures( const QString &filter )
+{
+  QgsExpressionContext context( QgsExpressionContextUtils::globalProjectLayerScopes( mLayer ) );
+
+  QgsFeatureRequest request = QgsFeatureRequest().setFilterExpression( filter )
+                              .setFlags( QgsFeatureRequest::NoGeometry )
+                              .setExpressionContext( context )
+                              .setSubsetOfAttributes( QgsAttributeList() );
+
+  QgsFeatureIterator features = mLayer->getFeatures( request );
+  QgsFeature feat;
+  QgsFeatureIds ids;
+  while ( features.nextFeature( feat ) )
+  {
+    ids.insert( feat.id() );
+  }
+
+  QgsSettings settings;
+  int timeout = settings.value( QStringLiteral( "qgis/messageTimeout" ), 5 ).toInt();
+  if ( !ids.empty() )
+  {
+    mMapCanvas->flashFeatureIds( mLayer, ids );
+  }
+  else if ( mMessageBar )
+  {
+    mMessageBar->pushMessage( QString(),
+                              tr( "No matching features found" ),
+                              QgsMessageBar::INFO,
+                              timeout );
+  }
+}

src/app/qgsselectbyformdialog.h

@@ -64,6 +64,7 @@ class APP_EXPORT QgsSelectByFormDialog : public QDialog
   private slots:
 
     void zoomToFeatures( const QString &filter );
+    void flashFeatures( const QString &filter );
 
   private:
 

src/gui/attributetable/qgsdualview.cpp

@@ -540,6 +540,7 @@ void QgsDualView::viewWillShowContextMenu( QMenu *menu, const QModelIndex &atInd
   {
     menu->addAction( tr( "Zoom to feature" ), this, SLOT( zoomToCurrentFeature() ) );
     menu->addAction( tr( "Pan to feature" ), this, SLOT( panToCurrentFeature() ) );
+    menu->addAction( tr( "Flash feature" ), this, SLOT( flashCurrentFeature() ) );
   }
 
   //add user-defined actions to context menu
@@ -780,6 +781,23 @@ void QgsDualView::panToCurrentFeature()
   }
 }
 
+void QgsDualView::flashCurrentFeature()
+{
+  QModelIndex currentIndex = mTableView->currentIndex();
+  if ( !currentIndex.isValid() )
+  {
+    return;
+  }
+
+  QgsFeatureIds ids;
+  ids.insert( mFilterModel->rowToId( currentIndex ) );
+  QgsMapCanvas *canvas = mFilterModel->mapCanvas();
+  if ( canvas )
+  {
+    canvas->flashFeatureIds( mLayer, ids );
+  }
+}
+
 void QgsDualView::rebuildFullLayerCache()
 {
   connect( mLayerCache, &QgsVectorLayerCache::progress, this, &QgsDualView::progress, Qt::UniqueConnection );

src/gui/attributetable/qgsdualview.h

@@ -328,6 +328,8 @@ class GUI_EXPORT QgsDualView : public QStackedWidget, private Ui::QgsDualViewBas
     //! Pans to the active feature
     void panToCurrentFeature();
 
+    void flashCurrentFeature();
+
     void rebuildFullLayerCache();
 
   private:

src/gui/qgsattributeform.cpp

@@ -410,6 +410,15 @@ void QgsAttributeForm::searchZoomTo()
   emit zoomToFeatures( filter );
 }
 
+void QgsAttributeForm::searchFlash()
+{
+  QString filter = createFilterExpression();
+  if ( filter.isEmpty() )
+    return;
+
+  emit flashFeatures( filter );
+}
+
 void QgsAttributeForm::filterAndTriggered()
 {
   QString filter = createFilterExpression();
@@ -1353,6 +1362,12 @@ void QgsAttributeForm::init()
     boxLayout->addWidget( clearButton );
     boxLayout->addStretch( 1 );
 
+    QPushButton *flashButton = new QPushButton();
+    flashButton->setSizePolicy( QSizePolicy::Minimum, QSizePolicy::Minimum );
+    flashButton->setText( tr( "&Flash features" ) );
+    connect( flashButton, &QToolButton::clicked, this, &QgsAttributeForm::searchFlash );
+    boxLayout->addWidget( flashButton );
+
     QPushButton *zoomButton = new QPushButton();
     zoomButton->setSizePolicy( QSizePolicy::Minimum, QSizePolicy::Minimum );
     zoomButton->setText( tr( "&Zoom to features" ) );

src/gui/qgsattributeform.h

@@ -202,6 +202,12 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
      */
     void zoomToFeatures( const QString &filter );
 
+    /**
+     * Emitted when the user chooses to flash a filtered set of features.
+     * \since QGIS 3.0
+     */
+    void flashFeatures( const QString &filter );
+
   public slots:
 
     /**
@@ -263,6 +269,7 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     void filterTriggered();
 
     void searchZoomTo();
+    void searchFlash();
     void searchSetSelection();
     void searchAddToSelection();
     void searchRemoveFromSelection();

src/gui/qgsmapcanvas.cpp

@@ -1058,6 +1058,101 @@ void QgsMapCanvas::panToSelected( QgsVectorLayer *layer )
   refresh();
 }
 
+void QgsMapCanvas::flashFeatureIds( QgsVectorLayer *layer, const QgsFeatureIds &ids,
+                                    const QColor &color1, const QColor &color2,
+                                    int flashes, int duration )
+{
+  if ( !layer )
+  {
+    return;
+  }
+
+  QList< QgsGeometry > geoms;
+
+  QgsFeatureIterator it = layer->getFeatures( QgsFeatureRequest().setFilterFids( ids ).setSubsetOfAttributes( QgsAttributeList() ) );
+  QgsFeature fet;
+  while ( it.nextFeature( fet ) )
+  {
+    if ( !fet.hasGeometry() )
+      continue;
+    geoms << fet.geometry();
+  }
+
+  if ( geoms.isEmpty() )
+    return;
+
+  QgsWkbTypes::GeometryType geomType = QgsWkbTypes::geometryType( layer->wkbType() );
+  QgsRubberBand *rb = new QgsRubberBand( this, geomType );
+  for ( const QgsGeometry &geom : qgsAsConst( geoms ) )
+    rb->addGeometry( geom, layer );
+
+  if ( geomType == QgsWkbTypes::LineGeometry || geomType == QgsWkbTypes::PointGeometry )
+  {
+    rb->setWidth( 2 );
+    rb->setSecondaryStrokeColor( QColor( 255, 255, 255 ) );
+  }
+  if ( geomType == QgsWkbTypes::PointGeometry )
+    rb->setIcon( QgsRubberBand::ICON_CIRCLE );
+
+  QColor startColor = color1;
+  if ( !startColor.isValid() )
+  {
+    if ( geomType == QgsWkbTypes::PolygonGeometry )
+    {
+      startColor = rb->fillColor();
+    }
+    else
+    {
+      startColor = rb->strokeColor();
+    }
+    startColor.setAlpha( 255 );
+  }
+  QColor endColor = color2;
+  if ( !endColor.isValid() )
+  {
+    endColor = startColor;
+    endColor.setAlpha( 0 );
+  }
+
+
+  QVariantAnimation *animation = new QVariantAnimation( this );
+  connect( animation, &QVariantAnimation::finished, this, [animation, rb]
+  {
+    animation->deleteLater();
+    delete rb;
+  } );
+  connect( animation, &QPropertyAnimation::valueChanged, this, [rb, geomType]( const QVariant & value )
+  {
+    QColor c = value.value<QColor>();
+    if ( geomType == QgsWkbTypes::PolygonGeometry )
+    {
+      rb->setFillColor( c );
+    }
+    else
+    {
+      rb->setStrokeColor( c );
+      QColor c = rb->secondaryStrokeColor();
+      c.setAlpha( c.alpha() );
+      rb->setSecondaryStrokeColor( c );
+    }
+    rb->update();
+  } );
+
+  animation->setDuration( duration * flashes );
+  animation->setStartValue( endColor );
+  double midStep = 0.2 / flashes;
+  for ( int i = 0; i < flashes; ++i )
+  {
+    double start = static_cast< double >( i ) / flashes;
+    animation->setKeyValueAt( start + midStep, startColor );
+    double end = static_cast< double >( i + 1 ) / flashes;
+    if ( !qgsDoubleNear( end, 1.0 ) )
+      animation->setKeyValueAt( end, endColor );
+  }
+  animation->setEndValue( endColor );
+  animation->start();
+}
+
 void QgsMapCanvas::keyPressEvent( QKeyEvent *e )
 {
   if ( mCanvasProperties->mouseButtonDown || mCanvasProperties->panSelectorDown )

src/gui/qgsmapcanvas.h

@@ -236,6 +236,19 @@ class GUI_EXPORT QgsMapCanvas : public QGraphicsView
     //! Pan to the selected features of current (vector) layer keeping same extent.
     void panToSelected( QgsVectorLayer *layer = nullptr );
 
+    /**
+     * Causes a set of features with matching \a ids from a vector \a layer to flash
+     * within the canvas.
+     *
+     * The \a startColor and \a endColor can be specified, along with the number of
+     * \a flashes and \a duration of each flash (in milliseconds).
+     *
+     * \since QGIS 3.0
+     */
+    void flashFeatureIds( QgsVectorLayer *layer, const QgsFeatureIds &ids,
+                          const QColor &startColor = QColor( 255, 0, 0, 255 ), const QColor &endColor = QColor( 255, 0, 0, 0 ),
+                          int flashes = 3, int duration = 500 );
+
     //! \brief Sets the map tool currently being used on the canvas
     void setMapTool( QgsMapTool *mapTool );