Provide custom project open handlers a method to create thumbnail images

for the welcome screen

python/gui/auto_generated/qgscustomprojectopenhandler.sip.in

@@ -46,6 +46,18 @@ The base class implementation does nothing.
 Returns file filters associated with this handler, e.g. "MXD Documents (*.mxd)", "MapInfo Workspaces (*.wor)".
 
 Each individual filter should be reflected as one entry in the returned list.
+%End
+
+    virtual bool createDocumentThumbnailAfterOpen() const;
+%Docstring
+Returns ``True`` if a document thumbnail should automatically be created after opening the project.
+
+The default behavior is to return ``False``.
+%End
+
+    virtual QIcon icon() const;
+%Docstring
+Returns a custom icon used to represent this handler.
 %End
 };
 

src/app/qgisapp.cpp

@@ -4897,7 +4897,7 @@ void QgisApp::updateRecentProjectPaths()
 }
 
 // add this file to the recently opened/saved projects list
-void QgisApp::saveRecentProjectPath( bool savePreviewImage )
+void QgisApp::saveRecentProjectPath( bool savePreviewImage, const QIcon &iconOverlay )
 {
   // first, re-read the recent project paths. This prevents loss of recent
   // projects when multiple QGIS sessions are open
@@ -4933,7 +4933,7 @@ void QgisApp::saveRecentProjectPath( bool savePreviewImage )
     projectData.previewImagePath = QStringLiteral( "%1/%2.png" ).arg( previewDir, fileName );
     QDir().mkdir( previewDir );
 
-    createPreviewImage( projectData.previewImagePath );
+    createPreviewImage( projectData.previewImagePath, iconOverlay );
   }
   else
   {
@@ -6682,17 +6682,21 @@ bool QgisApp::addProject( const QString &projectFile )
   mLayerTreeCanvasBridge->setAutoSetupOnFirstLayer( false );
 
   // give custom handlers a chance first
-  bool handled = false;
+  bool usedCustomHandler = false;
+  bool customHandlerWantsThumbnail = false;
+  QIcon customHandlerIcon;
   for ( QgsCustomProjectOpenHandler *handler : qgis::as_const( mCustomProjectOpenHandlers ) )
   {
     if ( handler && handler->handleProjectOpen( projectFile ) )
     {
-      handled = true;
+      usedCustomHandler = true;
+      customHandlerWantsThumbnail = handler->createDocumentThumbnailAfterOpen();
+      customHandlerIcon = handler->icon();
       break;
     }
   }
 
-  if ( !handled && !QgsProject::instance()->read( projectFile ) && !QgsZipUtils::isZipFile( projectFile ) )
+  if ( !usedCustomHandler && !QgsProject::instance()->read( projectFile ) && !QgsZipUtils::isZipFile( projectFile ) )
   {
     QString backupFile = projectFile + "~";
     QString loadBackupPrompt;
@@ -6785,7 +6789,20 @@ bool QgisApp::addProject( const QString &projectFile )
     // specific plug-in state
 
     // add this to the list of recently used project files
-    saveRecentProjectPath( false );
+    // if a custom handler was used, then we generate a thumbnail
+    if ( !usedCustomHandler || !customHandlerWantsThumbnail )
+      saveRecentProjectPath( false );
+    else if ( !QgsProject::instance()->fileName().isEmpty() )
+    {
+      // we have to delay the thumbnail creation until after the canvas has refreshed for the first time
+      QMetaObject::Connection *connection = new QMetaObject::Connection();
+      *connection = connect( mMapCanvas, &QgsMapCanvas::mapCanvasRefreshed, [ = ]()
+      {
+        QObject::disconnect( *connection );
+        delete connection;
+        saveRecentProjectPath( true, customHandlerIcon );
+      } );
+    }
 
     QApplication::restoreOverrideCursor();
 
@@ -14636,7 +14653,7 @@ void QgisApp::generateProjectAttachedFiles( QgsStringMap &files )
   previewImage->deleteLater();
 }
 
-void QgisApp::createPreviewImage( const QString &path )
+void QgisApp::createPreviewImage( const QString &path, const QIcon &icon )
 {
   // Render the map canvas
   QSize previewSize( 250, 177 ); // h = w / std::sqrt(2)
@@ -14648,6 +14665,13 @@ void QgisApp::createPreviewImage( const QString &path )
   QPainter previewPainter( &previewImage );
   mMapCanvas->render( &previewPainter, QRect( QPoint(), previewSize ), previewRect );
 
+  if ( !icon.isNull() )
+  {
+    QPixmap pixmap = icon.pixmap( QSize( 24, 24 ) );
+    previewPainter.drawPixmap( QPointF( 250 - 24 - 5, 177 - 24 - 5 ), pixmap );
+  }
+  previewPainter.end();
+
   // Save
   previewImage.save( path );
 }

src/app/qgisapp.h

@@ -1863,7 +1863,7 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     void activeLayerChanged( QgsMapLayer *layer );
 
   private:
-    void createPreviewImage( const QString &path );
+    void createPreviewImage( const QString &path, const QIcon &overlayIcon = QIcon() );
     void startProfile( const QString &name );
     void endProfile();
     void functionProfile( void ( QgisApp::*fnc )(), QgisApp *instance, const QString &name );
@@ -1918,8 +1918,9 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
      * instance simultaneously results in data loss.
      *
      * \param savePreviewImage Set to false when the preview image should not be saved. E.g. project load.
+     * \param iconOverlay optional icon to overlay when saving a preview image
      */
-    void saveRecentProjectPath( bool savePreviewImage = true );
+    void saveRecentProjectPath( bool savePreviewImage = true, const QIcon &iconOverlay = QIcon() );
     //! Save recent projects list to settings
     void saveRecentProjects();
     //! Update project menu with the current list of recently accessed projects

src/gui/qgscustomprojectopenhandler.cpp

@@ -14,3 +14,14 @@
  ***************************************************************************/
 
 #include "qgscustomprojectopenhandler.h"
+#include <QIcon>
+
+bool QgsCustomProjectOpenHandler::createDocumentThumbnailAfterOpen() const
+{
+  return false;
+}
+
+QIcon QgsCustomProjectOpenHandler::icon() const
+{
+  return QIcon();
+}

src/gui/qgscustomprojectopenhandler.h

@@ -58,6 +58,18 @@ class GUI_EXPORT QgsCustomProjectOpenHandler : public QObject
      * Each individual filter should be reflected as one entry in the returned list.
      */
     virtual QStringList filters() const = 0;
+
+    /**
+     * Returns TRUE if a document thumbnail should automatically be created after opening the project.
+     *
+     * The default behavior is to return FALSE.
+     */
+    virtual bool createDocumentThumbnailAfterOpen() const;
+
+    /**
+     * Returns a custom icon used to represent this handler.
+     */
+    virtual QIcon icon() const;
 };
 
 #endif // QgsCustomProjectOpenHandler_H