When labelling job takes a long time to render, don't clear the

map canvas between the finished layer render state and final state Avoids map canvas blanking out during a redraw while the labeling stage is underway, and instead correctly uses the nice layer cache preview instead.
qgis · Feb 9, 2021 · 1beb1bd · 1beb1bd
1 parent c661359
commit 1beb1bd
Showing 1 changed file with 6 additions and 1 deletion.
diff --git a/src/core/qgsmaprendererparalleljob.cpp b/src/core/qgsmaprendererparalleljob.cpp
@@ -209,7 +209,12 @@ QgsLabelingResults *QgsMapRendererParallelJob::takeLabelingResults()
 
 QImage QgsMapRendererParallelJob::renderedImage()
 {
-  if ( mStatus == RenderingLayers )
+  // if status == Idle we are either waiting for the render to start, OR have finished the render completely.
+  // We can differentiate between those states by checking whether mFinalImage is null -- at the "waiting for
+  // render to start" state mFinalImage has not yet been created.
+  const bool jobIsComplete = mStatus == Idle && !mFinalImage.isNull();
+
+  if ( !jobIsComplete )
     return composeImage( mSettings, mLayerJobs, mLabelJob, mCache );
   else
     return mFinalImage; // when rendering labels or idle