Merge pull request #5037 from nyalldawson/render_progress_bar

Avoid 'flashy' status bar progress widget when map renders are fast

src/app/qgisapp.cpp

@@ -8283,11 +8283,32 @@ void QgisApp::refreshMapCanvas()
 
 void QgisApp::canvasRefreshStarted()
 {
-  showProgress( -1, 0 ); // trick to make progress bar show busy indicator
+  mLastRenderTime.restart();
+  // if previous render took less than 0.5 seconds, delay the appearance of the
+  // render in progress status bar by 0.5 seconds - this avoids the status bar
+  // rapidly appearing and then disappearing for very fast renders
+  if ( mLastRenderTimeSeconds > 0 && mLastRenderTimeSeconds < 0.5 )
+  {
+    mRenderProgressBarTimer.setSingleShot( true );
+    mRenderProgressBarTimer.setInterval( 500 );
+    disconnect( mRenderProgressBarTimerConnection );
+    mRenderProgressBarTimerConnection = connect( &mRenderProgressBarTimer, &QTimer::timeout, [ = ]()
+    {
+      showProgress( -1, 0 );
+    }
+                                               );
+    mRenderProgressBarTimer.start();
+  }
+  else
+  {
+    showProgress( -1, 0 ); // trick to make progress bar show busy indicator
+  }
 }
 
 void QgisApp::canvasRefreshFinished()
 {
+  mRenderProgressBarTimer.stop();
+  mLastRenderTimeSeconds = mLastRenderTime.elapsed() / 1000.0;
   showProgress( 0, 0 ); // stop the busy indicator
 }
 

src/app/qgisapp.h

@@ -2067,6 +2067,11 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
 
     QgsStatusBar *mStatusBar = nullptr;
 
+    QTime mLastRenderTime;
+    double mLastRenderTimeSeconds = 0;
+    QTimer mRenderProgressBarTimer;
+    QMetaObject::Connection mRenderProgressBarTimerConnection;
+
     friend class TestQgisAppPython;
 };