Also show a preview tooltip for symbol buttons

Author: nyalldawson

src/gui/qgssymbolbutton.cpp

@@ -470,6 +470,15 @@ void QgsSymbolButton::updatePreview( const QColor &color, QgsSymbol *tempSymbol
   QIcon icon = QgsSymbolLayerUtils::symbolPreviewIcon( previewSymbol.get(), currentIconSize );
   setIconSize( currentIconSize );
   setIcon( icon );
+
+  // set tooltip
+  // create very large preview image
+  int size = static_cast< int >( Qgis::UI_SCALE_FACTOR * fontMetrics().width( 'X' ) * 20 );
+  QPixmap pm = QgsSymbolLayerUtils::symbolPreviewPixmap( previewSymbol.get(), QSize( size, size ), size / 20 );
+  QByteArray data;
+  QBuffer buffer( &data );
+  pm.save( &buffer, "PNG", 100 );
+  setToolTip( QStringLiteral( "<img src='data:image/png;base64, %3'>" ).arg( QString( data.toBase64() ) ) );
 }
 
 bool QgsSymbolButton::colorFromMimeData( const QMimeData *mimeData, QColor &resultColor, bool &hasAlpha )