Faster multiband color renderer in some circumstances

src/core/raster/qgsmultibandcolorrenderer.cpp

@@ -267,23 +267,44 @@ QgsRasterBlock *QgsMultiBandColorRenderer::block( int bandNo, QgsRectangle  cons
   {
     if ( fastDraw ) //fast rendering if no transparency, stretching, color inversion, etc.
     {
-      if ( redBlock->isNoData( i ) ||
-           greenBlock->isNoData( i ) ||
-           blueBlock->isNoData( i ) )
+      if ( hasByteRgb )
       {
-        outputBlock->setColor( i, myDefaultColor );
+        if ( redBlock->isNoData( i ) ||
+             greenBlock->isNoData( i ) ||
+             blueBlock->isNoData( i ) )
+        {
+          outputBlock->setColor( i, myDefaultColor );
+        }
+        else
+        {
+          outputBlockColorData[i] = qRgb( redData[i], greenData[i], blueData[i] );
+        }
       }
       else
       {
-        if ( hasByteRgb )
+        bool redIsNoData = false;
+        bool greenIsNoData = false;
+        bool blueIsNoData = false;
+        int redVal = 0;
+        int greenVal = 0;
+        int blueVal = 0;
+
+        redVal = redBlock->valueAndNoData( i, redIsNoData );
+        // as soon as any channel has a no data value, don't do any more work -- the result will
+        // always be the nodata color!
+        if ( !redIsNoData )
+          greenVal = greenBlock->valueAndNoData( i, greenIsNoData );
+        if ( !redIsNoData && !greenIsNoData )
+          blueVal = blueBlock->valueAndNoData( i, blueIsNoData );
+
+        if ( redIsNoData ||
+             greenIsNoData ||
+             blueIsNoData )
         {
-          outputBlockColorData[i] = qRgb( redData[i], greenData[i], blueData[i] );
+          outputBlock->setColor( i, myDefaultColor );
         }
         else
         {
-          int redVal = static_cast<int>( redBlock->value( i ) );
-          int greenVal = static_cast<int>( greenBlock->value( i ) );
-          int blueVal = static_cast<int>( blueBlock->value( i ) );
           outputBlockColorData[i] = qRgb( redVal, greenVal, blueVal );
         }
       }