Non-default blend mode should force raster render of layer

Fixes rendering of vector tile and annotation layers with non
default blend modes in layouts

Fixes qgis#55629

(cherry picked from commit 9ed009f)

src/core/annotations/qgsannotationlayerrenderer.cpp

@@ -26,6 +26,7 @@ QgsAnnotationLayerRenderer::QgsAnnotationLayerRenderer( QgsAnnotationLayer *laye
   : QgsMapLayerRenderer( layer->id(), &context )
   , mFeedback( std::make_unique< QgsFeedback >() )
   , mLayerOpacity( layer->opacity() )
+  , mLayerBlendMode( layer->blendMode() )
 {
   // Clone items from layer which fall inside the rendered extent
   // Because some items have scale dependent bounds, we have to accept some limitations here.
@@ -111,5 +112,14 @@ bool QgsAnnotationLayerRenderer::render()
 
 bool QgsAnnotationLayerRenderer::forceRasterRender() const
 {
-  return renderContext()->testFlag( Qgis::RenderContextFlag::UseAdvancedEffects ) && ( !qgsDoubleNear( mLayerOpacity, 1.0 ) );
+  if ( !renderContext()->testFlag( Qgis::RenderContextFlag::UseAdvancedEffects ) )
+    return false;
+
+  if ( !qgsDoubleNear( mLayerOpacity, 1.0 ) )
+    return true;
+
+  if ( mLayerBlendMode != QPainter::CompositionMode_SourceOver )
+    return true;
+
+  return false;
 }

src/core/annotations/qgsannotationlayerrenderer.h

@@ -54,6 +54,7 @@ class CORE_EXPORT QgsAnnotationLayerRenderer : public QgsMapLayerRenderer
     std::vector < std::pair< QString, std::unique_ptr< QgsAnnotationItem > > > mItems;
     std::unique_ptr< QgsFeedback > mFeedback;
     double mLayerOpacity = 1.0;
+    QPainter::CompositionMode mLayerBlendMode = QPainter::CompositionMode::CompositionMode_SourceOver;
     std::unique_ptr< QgsPaintEffect > mPaintEffect;
 
 };

src/core/vectortile/qgsvectortilelayerrenderer.cpp

@@ -38,6 +38,7 @@ QgsVectorTileLayerRenderer::QgsVectorTileLayerRenderer( QgsVectorTileLayer *laye
   , mLayerName( layer->name() )
   , mDataProvider( qgis::down_cast< const QgsVectorTileDataProvider* >( layer->dataProvider() )->clone() )
   , mRenderer( layer->renderer()->clone() )
+  , mLayerBlendMode( layer->blendMode() )
   , mDrawTileBoundaries( layer->isTileBorderRenderingEnabled() )
   , mLabelsEnabled( layer->labelsEnabled() )
   , mFeedback( new QgsFeedback )
@@ -237,7 +238,16 @@ bool QgsVectorTileLayerRenderer::render()
 
 bool QgsVectorTileLayerRenderer::forceRasterRender() const
 {
-  return renderContext()->testFlag( Qgis::RenderContextFlag::UseAdvancedEffects ) && ( !qgsDoubleNear( mLayerOpacity, 1.0 ) );
+  if ( !renderContext()->testFlag( Qgis::RenderContextFlag::UseAdvancedEffects ) )
+    return false;
+
+  if ( !qgsDoubleNear( mLayerOpacity, 1.0 ) )
+    return true;
+
+  if ( mLayerBlendMode != QPainter::CompositionMode_SourceOver )
+    return true;
+
+  return false;
 }
 
 void QgsVectorTileLayerRenderer::decodeAndDrawTile( const QgsVectorTileRawData &rawTile )

src/core/vectortile/qgsvectortilelayerrenderer.h

@@ -63,6 +63,8 @@ class QgsVectorTileLayerRenderer : public QgsMapLayerRenderer
     //! Tile renderer object to do rendering of individual tiles
     std::unique_ptr<QgsVectorTileRenderer> mRenderer;
 
+    QPainter::CompositionMode mLayerBlendMode = QPainter::CompositionMode::CompositionMode_SourceOver;
+
     /**
      * Label provider that handles registration of labels.
      * No need to delete: if exists it is owned by labeling engine.

tests/src/python/test_qgsannotationlayer.py

@@ -598,6 +598,25 @@ def test_render_via_job_with_transform(self):
         self.assertTrue(compareWkt(result, expected, tol=1000), "mismatch Expected:\n{}\nGot:\n{}\n".format(expected,
                                                                                                             result))
 
+    def test_force_raster_render(self):
+        layer = QgsAnnotationLayer('test', QgsAnnotationLayer.LayerOptions(QgsProject.instance().transformContext()))
+        self.assertTrue(layer.isValid())
+        settings = QgsMapSettings()
+        rc = QgsRenderContext.fromMapSettings(settings)
+        renderer = layer.createMapRenderer(rc)
+        self.assertFalse(renderer.forceRasterRender())
+
+        # layer opacity should force raster render
+        layer.setOpacity(0.5)
+        renderer = layer.createMapRenderer(rc)
+        self.assertTrue(renderer.forceRasterRender())
+        layer.setOpacity(1.0)
+
+        # alternate blend mode should force raster render
+        layer.setBlendMode(QPainter.CompositionMode.CompositionMode_Multiply)
+        renderer = layer.createMapRenderer(rc)
+        self.assertTrue(renderer.forceRasterRender())
+
 
 if __name__ == '__main__':
     unittest.main()

tests/src/python/test_qgsvectortile.py

@@ -20,6 +20,7 @@
 
 import qgis  # NOQA
 from qgis.PyQt.QtTest import QSignalSpy
+from qgis.PyQt.QtGui import QPainter
 from qgis.core import (
     Qgis,
     QgsDataSourceUri,
@@ -30,6 +31,8 @@
     QgsVectorLayer,
     QgsVectorTileLayer,
     QgsVectorTileWriter,
+    QgsMapSettings,
+    QgsRenderContext
 )
 import unittest
 from qgis.testing import start_app, QgisTestCase
@@ -295,6 +298,25 @@ def testSelection(self):
         self.assertCountEqual({f.geometry().asWkt(-3) for f in layer.selectedFeatures()}, {'Polygon ((-10958000 3835000, -10958000 3796000, -10919000 3835000, -10841000 3874000, -10684000 3992000, -10567000 4031000, -10410000 4031000, -10332000 3992000, -10254000 3914000, -10136000 3914000, -10058000 3874000, -10019000 3796000, -10019000 3757000, -10058000 3718000, -10097000 3718000, -10254000 3796000, -10332000 3796000, -10371000 3757000, -10371000 3718000, -10371000 3679000, -10332000 3640000, -10332000 3561000, -10410000 3483000, -10449000 3405000, -10488000 3366000, -10645000 3327000, -10723000 3366000, -10762000 3405000, -10801000 3444000, -10762000 3483000, -10801000 3522000, -10841000 3561000, -10919000 3561000, -10958000 3600000, -10958000 3640000, -10958000 3679000, -10958000 3718000, -10997000 3796000, -10958000 3835000))'})
         self.assertEqual(len(spy), 11)
 
+    def test_force_raster_render(self):
+        layer = QgsVectorTileLayer(f"type=vtpk&url={unitTestDataPath() + '/testvtpk.vtpk'}", 'tiles')
+        self.assertTrue(layer.isValid())
+        settings = QgsMapSettings()
+        rc = QgsRenderContext.fromMapSettings(settings)
+        renderer = layer.createMapRenderer(rc)
+        self.assertFalse(renderer.forceRasterRender())
+
+        # layer opacity should force raster render
+        layer.setOpacity(0.5)
+        renderer = layer.createMapRenderer(rc)
+        self.assertTrue(renderer.forceRasterRender())
+        layer.setOpacity(1.0)
+
+        # alternate blend mode should force raster render
+        layer.setBlendMode(QPainter.CompositionMode.CompositionMode_Multiply)
+        renderer = layer.createMapRenderer(rc)
+        self.assertTrue(renderer.forceRasterRender())
+
 
 if __name__ == '__main__':
     unittest.main()