WMS server: even more performant png8 conversion

Author: mhugent

src/mapserver/qgshttprequesthandler.cpp

@@ -115,9 +115,33 @@ void QgsHttpRequestHandler::sendGetMapResponse( const QString& service, QImage*
     if ( png8Bit )
     {
       QVector<QRgb> colorTable;
-      medianCut( colorTable, 256, *img );
-      QImage palettedImg = img->convertToFormat( QImage::Format_Indexed8, colorTable, Qt::ColorOnly | Qt::ThresholdDither |
-                           Qt::ThresholdAlphaDither | Qt::NoOpaqueDetection );
+      QHash<QRgb, int> colorIndexHash;
+      medianCut( colorTable, colorIndexHash, 256, *img );
+
+
+      QImage palettedImg( img->size(), QImage::Format_Indexed8 );
+      palettedImg.setColorTable( colorTable );
+
+      int h = img->height();
+      int w = img->width();
+
+      for ( int y = 0; y < h; ++y )
+      {
+        QRgb* src_pixels = ( QRgb * ) img->scanLine( y );
+        uchar* dest_pixels = ( uchar * ) palettedImg.scanLine( y );
+
+        for ( int x = 0; x < w; ++x )
+        {
+          int src_pixel = src_pixels[x];
+          int value = colorIndexHash.value( src_pixel, -1 );
+          if ( value == -1 )
+          {
+            continue;
+          }
+          dest_pixels[x] = ( uchar ) value;
+        }
+      }
+
       palettedImg.save( &buffer, "PNG", -1 );
     }
     else if ( png16Bit )
@@ -502,7 +526,7 @@ QString QgsHttpRequestHandler::readPostBody() const
   return inputString;
 }
 
-void QgsHttpRequestHandler::medianCut( QVector<QRgb>& colorTable, int nColors, const QImage& inputImage )
+void QgsHttpRequestHandler::medianCut( QVector<QRgb>& colorTable, QHash<QRgb, int>& colorIndexHash, int nColors, const QImage& inputImage )
 {
   QHash<QRgb, int> inputColors;
   imageColors( inputColors, inputImage );
@@ -571,7 +595,7 @@ void QgsHttpRequestHandler::medianCut( QVector<QRgb>& colorTable, int nColors, c
   QgsColorBoxMap::const_iterator colorBoxIt = colorBoxMap.constBegin();
   for ( ; colorBoxIt != colorBoxMap.constEnd(); ++colorBoxIt )
   {
-    colorTable[index] = boxColor( colorBoxIt.value(), colorBoxIt.key() );
+    colorTable[index] = boxColor( colorBoxIt.value(), colorBoxIt.key(), index, colorIndexHash );
     ++index;
   }
 }
@@ -765,7 +789,7 @@ bool QgsHttpRequestHandler::alphaCompare( const QPair<QRgb, int>& c1, const QPai
   return qAlpha( c1.first ) < qAlpha( c2.first );
 }
 
-QRgb QgsHttpRequestHandler::boxColor( const QgsColorBox& box, int boxPixels )
+QRgb QgsHttpRequestHandler::boxColor( const QgsColorBox& box, int boxPixels, int colorMapIndex, QHash<QRgb, int>& colorIndexHash )
 {
   double avRed = 0;
   double avGreen = 0;
@@ -786,6 +810,8 @@ QRgb QgsHttpRequestHandler::boxColor( const QgsColorBox& box, int boxPixels )
     avGreen += ( qGreen( currentColor ) * weight );
     avBlue += ( qBlue( currentColor ) * weight );
     avAlpha += ( qAlpha( currentColor ) * weight );
+    //allow faster lookup in image conversion
+    colorIndexHash.insert( currentColor, colorMapIndex );
   }
 
   return qRgba( avRed, avGreen, avBlue, avAlpha );

src/mapserver/qgshttprequesthandler.h

@@ -55,7 +55,7 @@ class QgsHttpRequestHandler: public QgsRequestHandler
     QString readPostBody() const;
 
   private:
-    static void medianCut( QVector<QRgb>& colorTable, int nColors, const QImage& inputImage );
+    static void medianCut( QVector<QRgb>& colorTable, QHash<QRgb, int>& colorIndexHash, int nColors, const QImage& inputImage );
     static void imageColors( QHash<QRgb, int>& colors, const QImage& image );
     static void splitColorBox( QgsColorBox& colorBox, QgsColorBoxMap& colorBoxMap,
                                QMap<int, QgsColorBox>::iterator colorBoxMapIt );
@@ -65,7 +65,7 @@ class QgsHttpRequestHandler: public QgsRequestHandler
     static bool blueCompare( const QPair<QRgb, int>& c1, const QPair<QRgb, int>& c2 );
     static bool alphaCompare( const QPair<QRgb, int>& c1, const QPair<QRgb, int>& c2 );
     /**Calculates a representative color for a box (pixel weighted average)*/
-    static QRgb boxColor( const QgsColorBox& box, int boxPixels );
+    static QRgb boxColor( const QgsColorBox& box, int boxPixels, int colorMapIndex, QHash<QRgb, int>& colorIndexHash );
 };
 
 #endif