SVN commit 1167901 by rahn:

Backport of 

SVN commit 1167566 by beschow:

add support for AlphaBlending

* this allows for hill shading in OSM, for instance

- Tested with hikebikemap.dgml
- virtual methods checked for identity of signature wrt binary
  compatibility



 M  +23 -0     BlendingAlgorithms.cpp  
 M  +6 -0      BlendingAlgorithms.h  
 M  +1 -0      BlendingFactory.cpp  


--- branches/KDE/4.5/kdeedu/marble/src/lib/blendings/BlendingAlgorithms.cpp #1167900:1167901
@@ -161,6 +161,28 @@
 
 // Lightening blendings
 
+void AlphaBlending::blend( QImage * const bottom, QSharedPointer< TextureTile > const & top ) const
+{
+    QImage const * const topImage = top->image();
+    Q_ASSERT( topImage );
+    Q_ASSERT( bottom->size() == topImage->size() );
+    int const width = bottom->width();
+    int const height = bottom->height();
+    for ( int y = 0; y < height; ++y ) {
+        for ( int x = 0; x < width; ++x ) {
+            qreal const c = qRed( topImage->pixel( x, y )) / 255.0;
+            qreal const alpha = qAlpha(topImage->pixel( x, y )) / 255.0;
+            QRgb const bottomPixel = bottom->pixel( x, y );
+            int const bottomRed = qRed( bottomPixel );
+            int const bottomGreen = qGreen( bottomPixel );
+            int const bottomBlue = qBlue( bottomPixel );
+            bottom->setPixel( x, y, qRgb(( int )( c * alpha + ( 1 - alpha ) * bottomRed ),
+                                         ( int )( c * alpha + ( 1 - alpha ) * bottomGreen ),
+                                         ( int )( c * alpha + ( 1 - alpha ) * bottomBlue )));
+        }
+    }
+}
+
 qreal AdditiveBlending::blendChannel( qreal const bottomColorIntensity,
                                       qreal const topColorIntensity ) const
 {
@@ -289,4 +311,5 @@
     }
 }
 
+
 }
--- branches/KDE/4.5/kdeedu/marble/src/lib/blendings/BlendingAlgorithms.h #1167900:1167901
@@ -139,6 +139,12 @@
 
 // Lightening blendings
 
+class AlphaBlending: public Blending
+{
+ public:
+    virtual void blend( QImage * const bottom, QSharedPointer<TextureTile> const & top ) const;
+};
+
 class AdditiveBlending: public IndependentChannelBlending
 {
     virtual qreal blendChannel( qreal const bottomColorIntensity,
--- branches/KDE/4.5/kdeedu/marble/src/lib/blendings/BlendingFactory.cpp #1167900:1167901
@@ -52,6 +52,7 @@
     //m_blendings.insert( "TextureBlending", new TextureBlending );
 
     // Darkening blendings
+    m_blendings.insert( "AlphaBlending", new AlphaBlending );
     m_blendings.insert( "ColorBurnBlending", new ColorBurnBlending );
     m_blendings.insert( "DarkBlending", new DarkBlending );
     m_blendings.insert( "DarkenBlending", new DarkenBlending );