Avoid texture jump when panning maps

We don't need the whole expense of the "Avoid artifacts when rendering as map tiles" option, because that disables to default clipping of geometry parts which fall outside the visible canvas extent and accordingly results in a lot of wasted rendering calculations. Instead, we can just always use the upper left corner of the original feature geometry before the optimisations like clipping to visible regions are applied, and use this as the texture origin. This means we can safely make this handling always applied and not an opt-in setting
qgis · Jul 11, 2020 · 28c8eef · 28c8eef
1 parent 81518f9
commit 28c8eef
Show file tree

Hide file tree

Showing 5 changed files with 66 additions and 1 deletion.
diff --git a/python/core/auto_generated/qgsrendercontext.sip.in b/python/core/auto_generated/qgsrendercontext.sip.in
@@ -841,6 +841,26 @@ Sets a ``geometry`` to use to clip features at render time.
 
 .. seealso:: :py:func:`featureClipGeometry`
 
+.. versionadded:: 3.16
+%End
+
+    QPointF textureOrigin() const;
+%Docstring
+Returns the texture origin, which should be used as a brush transform when
+rendering using QBrush objects.
+
+.. seealso:: :py:func:`setTextureOrigin`
+
+.. versionadded:: 3.16
+%End
+
+    void setTextureOrigin( const QPointF &origin );
+%Docstring
+Sets the texture ``origin``, which should be used as a brush transform when
+rendering using QBrush objects.
+
+.. seealso:: :py:func:`textureOrigin`
+
 .. versionadded:: 3.16
 %End
 

diff --git a/src/core/qgsrendercontext.cpp b/src/core/qgsrendercontext.cpp
@@ -69,6 +69,7 @@ QgsRenderContext::QgsRenderContext( const QgsRenderContext &rh )
   , mDisabledSymbolLayers()
   , mClippingRegions( rh.mClippingRegions )
   , mFeatureClipGeometry( rh.mFeatureClipGeometry )
+  , mTextureOrigin( rh.mTextureOrigin )
 #ifdef QGISDEBUG
   , mHasTransformContext( rh.mHasTransformContext )
 #endif
@@ -104,6 +105,7 @@ QgsRenderContext &QgsRenderContext::operator=( const QgsRenderContext &rh )
   mCustomRenderingFlags = rh.mCustomRenderingFlags;
   mClippingRegions = rh.mClippingRegions;
   mFeatureClipGeometry = rh.mFeatureClipGeometry;
+  mTextureOrigin = rh.mTextureOrigin;
   setIsTemporal( rh.isTemporal() );
   if ( isTemporal() )
     setTemporalRange( rh.temporalRange() );
@@ -534,4 +536,14 @@ void QgsRenderContext::setFeatureClipGeometry( const QgsGeometry &geometry )
   mFeatureClipGeometry = geometry;
 }
 
+QPointF QgsRenderContext::textureOrigin() const
+{
+  return mTextureOrigin;
+}
+
+void QgsRenderContext::setTextureOrigin( const QPointF &origin )
+{
+  mTextureOrigin = origin;
+}
+
 
diff --git a/src/core/qgsrendercontext.h b/src/core/qgsrendercontext.h
@@ -836,6 +836,24 @@ class CORE_EXPORT QgsRenderContext : public QgsTemporalRangeObject
      */
     void setFeatureClipGeometry( const QgsGeometry &geometry );
 
+    /**
+     * Returns the texture origin, which should be used as a brush transform when
+     * rendering using QBrush objects.
+     *
+     * \see setTextureOrigin()
+     * \since QGIS 3.16
+     */
+    QPointF textureOrigin() const;
+
+    /**
+     * Sets the texture \a origin, which should be used as a brush transform when
+     * rendering using QBrush objects.
+     *
+     * \see textureOrigin()
+     * \since QGIS 3.16
+     */
+    void setTextureOrigin( const QPointF &origin );
+
   private:
 
     Flags mFlags;
@@ -930,6 +948,8 @@ class CORE_EXPORT QgsRenderContext : public QgsTemporalRangeObject
     QList< QgsMapClippingRegion > mClippingRegions;
     QgsGeometry mFeatureClipGeometry;
 
+    QPointF mTextureOrigin;
+
 #ifdef QGISDEBUG
     bool mHasTransformContext = false;
 #endif

diff --git a/src/core/symbology/qgsfillsymbollayer.cpp b/src/core/symbology/qgsfillsymbollayer.cpp
@@ -1597,7 +1597,14 @@ void QgsImageFillSymbolLayer::renderPolygon( const QPolygonF &points, const QVec
   p->setPen( QPen( Qt::NoPen ) );
 
   QTransform bkTransform = mBrush.transform();
-  if ( context.renderContext().testFlag( QgsRenderContext::RenderMapTile ) )
+  if ( !context.renderContext().textureOrigin().isNull() )
+  {
+    QPointF leftCorner = context.renderContext().textureOrigin();
+    QTransform t = mBrush.transform();
+    t.translate( leftCorner.x(), leftCorner.y() );
+    mBrush.setTransform( t );
+  }
+  else if ( context.renderContext().testFlag( QgsRenderContext::RenderMapTile ) )
   {
     //transform brush to upper left corner of geometry bbox
     QPointF leftCorner = points.boundingRect().topLeft();

diff --git a/src/core/symbology/qgssymbol.cpp b/src/core/symbology/qgssymbol.cpp
@@ -832,6 +832,12 @@ void QgsSymbol::renderFeature( const QgsFeature &feature, QgsRenderContext &cont
   bool usingSegmentizedGeometry = false;
   context.setGeometry( geom.constGet() );
 
+  if ( !geom.boundingBox().isNull() )
+  {
+    const QPointF boundsOrigin = _getPoint( context, QgsPoint( geom.boundingBox().xMinimum(), geom.boundingBox().yMinimum() ) );
+    context.setTextureOrigin( boundsOrigin );
+  }
+
   bool tileMapRendering = context.testFlag( QgsRenderContext::RenderMapTile );
 
   //convert curve types to normal point/line/polygon ones