Unlock composition using transformed previewed cache image of labeling

results as well as map layers This extends the recent addition of smooth map updates for raster layers to also apply to map labels. Now you'll see a scaled/transformed version of the previous map render's labels while the new labeling results are being generated in the background. Avoids "flashy" redraws of map labels
qgis · Jan 27, 2021 · c4818a0 · c4818a0
1 parent 0edd4f9
commit c4818a0
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Showing 4 changed files with 18 additions and 1 deletion.
diff --git a/python/core/auto_generated/qgsmaprendererjob.sip.in b/python/core/auto_generated/qgsmaprendererjob.sip.in
@@ -156,6 +156,7 @@ Returns map settings with which this job was started.
 %End
 
 
+
   signals:
 
     void renderingLayersFinished();

diff --git a/src/core/qgsmaprendererjob.cpp b/src/core/qgsmaprendererjob.cpp
@@ -47,6 +47,7 @@
 ///@cond PRIVATE
 
 const QString QgsMapRendererJob::LABEL_CACHE_ID = QStringLiteral( "_labels_" );
+const QString QgsMapRendererJob::LABEL_PREVIEW_CACHE_ID = QStringLiteral( "_preview_labels_" );
 
 bool LayerRenderJob::imageCanBeComposed() const
 {
@@ -750,6 +751,7 @@ void QgsMapRendererJob::cleanupLabelJob( LabelRenderJob &job )
     {
       QgsDebugMsgLevel( QStringLiteral( "caching label result image" ), 2 );
       mCache->setCacheImage( LABEL_CACHE_ID, *job.img, _qgis_listQPointerToRaw( job.participatingLayers ) );
+      mCache->setCacheImage( LABEL_PREVIEW_CACHE_ID, *job.img, _qgis_listQPointerToRaw( job.participatingLayers ) );
     }
 
     delete job.img;
@@ -816,6 +818,13 @@ QImage QgsMapRendererJob::composeImage(
     painter.setOpacity( 1.0 );
     painter.drawImage( 0, 0, *labelJob.img );
   }
+  else if ( cache && cache->hasAnyCacheImage( LABEL_PREVIEW_CACHE_ID ) )
+  {
+    const QImage labelCacheImage = cache->transformedCacheImage( LABEL_PREVIEW_CACHE_ID, settings.mapToPixel() );
+    painter.setCompositionMode( QPainter::CompositionMode_SourceOver );
+    painter.setOpacity( 1.0 );
+    painter.drawImage( 0, 0, labelCacheImage );
+  }
 
   // render any layers with the renderAboveLabels flag now
   for ( LayerRenderJobs::const_iterator it = jobs.constBegin(); it != jobs.constEnd(); ++it )

diff --git a/src/core/qgsmaprendererjob.h b/src/core/qgsmaprendererjob.h
@@ -325,6 +325,13 @@ class CORE_EXPORT QgsMapRendererJob : public QObject
      */
     static const QString LABEL_CACHE_ID SIP_SKIP;
 
+    /**
+     * QgsMapRendererCache ID string for cached label image during preview compositions only.
+     * \note not available in Python bindings
+     * \since QGIS 3.18
+     */
+    static const QString LABEL_PREVIEW_CACHE_ID SIP_SKIP;
+
   signals:
 
     /**

diff --git a/src/core/qgsmaprendererparalleljob.cpp b/src/core/qgsmaprendererparalleljob.cpp
@@ -231,7 +231,7 @@ void QgsMapRendererParallelJob::renderLayersFinished()
   // compose final image for labeling
   if ( mSecondPassLayerJobs.isEmpty() )
   {
-    mFinalImage = composeImage( mSettings, mLayerJobs, mLabelJob );
+    mFinalImage = composeImage( mSettings, mLayerJobs, mLabelJob, mCache );
   }
 
   QgsDebugMsgLevel( QStringLiteral( "PARALLEL layers finished" ), 2 );