Detect if transparency can be ignored for paletted renderer

Author: mhugent

src/core/raster/qgspalettedrasterrenderer.cpp

@@ -17,6 +17,7 @@
 
 #include "qgspalettedrasterrenderer.h"
 #include "qgsrastertransparency.h"
+#include "qgsrasterviewport.h"
 #include <QColor>
 #include <QImage>
 
@@ -61,7 +62,8 @@ void QgsPalettedRasterRenderer::draw( QPainter* p, QgsRasterViewPort* viewPort,
   void* rasterData;
   double currentOpacity = mOpacity;
 
-  bool hasTransparency = usesTransparency();
+  //rendering is faster without considering user-defined transparency
+  bool hasTransparency = usesTransparency( viewPort->mSrcCRS, viewPort->mDestCRS );
   void* transparencyData;
 
   while ( readNextRasterPart( mBandNumber, viewPort, nCols, nRows, &rasterData, topLeftCol, topLeftRow ) )

src/core/raster/qgsrasterrenderer.cpp

@@ -157,9 +157,15 @@ void QgsRasterRenderer::removePartInfo( int bandNumber )
   }
 }
 
-bool QgsRasterRenderer::usesTransparency() const
+bool QgsRasterRenderer::usesTransparency( QgsCoordinateReferenceSystem& srcSRS, QgsCoordinateReferenceSystem& dstSRS ) const
 {
-  return ( mAlphaBand > 0 || ( mRasterTransparency && !mRasterTransparency->isEmpty() ) || !doubleNear( mOpacity, 1.0 ) );
+  //transparency is always used if on-the-fly reprojection is enabled
+  bool reprojectionEnabled = ( srcSRS.isValid() && dstSRS.isValid() && srcSRS != dstSRS );
+  if ( !mProvider || reprojectionEnabled )
+  {
+    return true;
+  }
+  return ( mAlphaBand > 0 || ( mRasterTransparency && !mRasterTransparency->isEmpty( mProvider->noDataValue() ) ) || !doubleNear( mOpacity, 1.0 ) );
 }
 
 void QgsRasterRenderer::drawImage( QPainter* p, QgsRasterViewPort* viewPort, const QImage& img, int topLeftCol, int topLeftRow,

src/core/raster/qgsrasterrenderer.h

@@ -45,7 +45,7 @@ class QgsRasterRenderer
     virtual ~QgsRasterRenderer();
     virtual void draw( QPainter* p, QgsRasterViewPort* viewPort, const QgsMapToPixel* theQgsMapToPixel ) = 0;
 
-    bool usesTransparency() const;
+    bool usesTransparency( QgsCoordinateReferenceSystem& srcSRS, QgsCoordinateReferenceSystem& dstSRS ) const;
 
     void setOpacity( double opacity ) { mOpacity = opacity; }
     double opacity() const { return mOpacity; }

src/core/raster/qgsrastertransparency.cpp

@@ -18,6 +18,7 @@ email                : ersts@amnh.org
 #include <QList>
 
 #include "qgsrastertransparency.h"
+#include "qgis.h"
 
 QgsRasterTransparency::QgsRasterTransparency()
 {
@@ -169,7 +170,13 @@ int QgsRasterTransparency::alphaValue( double theRedValue, double theGreenValue,
   return theGlobalTransparency;
 }
 
-bool QgsRasterTransparency::isEmpty() const
+bool QgsRasterTransparency::isEmpty( double nodataValue ) const
 {
-  return ( mTransparentThreeValuePixelList.isEmpty() && mTransparentSingleValuePixelList.isEmpty() );
+  return (
+           ( mTransparentSingleValuePixelList.isEmpty() ||
+             ( mTransparentSingleValuePixelList.size() == 1 && doubleNear( mTransparentSingleValuePixelList.at( 0 ).pixelValue, nodataValue ) ) )
+           &&
+           ( mTransparentThreeValuePixelList.isEmpty() ||
+             ( mTransparentThreeValuePixelList.size() == 1 && doubleNear( mTransparentThreeValuePixelList.at( 0 ).red, nodataValue ) &&
+               doubleNear( mTransparentThreeValuePixelList.at( 0 ).green, nodataValue ) && doubleNear( mTransparentThreeValuePixelList.at( 0 ).blue, nodataValue ) ) ) );
 }

src/core/raster/qgsrastertransparency.h

@@ -72,8 +72,8 @@ class CORE_EXPORT QgsRasterTransparency
     /** \brief Return the transparency value for a RGB Pixel */
     int alphaValue( double, double, double, int theGlobalTransparency = 255 ) const;
 
-    /**True if there are no entries in the pixel lists*/
-    bool isEmpty() const;
+    /**True if there are no entries in the pixel lists except the nodata value*/
+    bool isEmpty( double nodataValue ) const;
 
   private:
     /** \brief The list to hold transparency values for RGB layers */