Create a better fake rendercontext for symbol previews

git-svn-id: http://svn.osgeo.org/qgis/trunk@12763 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: mhugent

src/core/symbology-ng/qgssymbollayerv2utils.cpp

@@ -660,3 +660,19 @@ double QgsSymbolLayerV2Utils::pixelSizeScaleFactor( QgsRenderContext& c, QgsSymb
     return c.rasterScaleFactor() / c.mapToPixel().mapUnitsPerPixel();
   }
 }
+
+QgsRenderContext QgsSymbolLayerV2Utils::createRenderContext( QPainter* p )
+{
+  QgsRenderContext context;
+  context.setPainter( p );
+  context.setRasterScaleFactor( 1.0 );
+  if ( p && p->device() )
+  {
+    context.setScaleFactor( p->device()->logicalDpiX() / 25.4 );
+  }
+  else
+  {
+    context.setScaleFactor( 3.465 ); //assume 88 dpi as standard value
+  }
+  return context;
+}

src/core/symbology-ng/qgssymbollayerv2utils.h

@@ -73,6 +73,8 @@ class CORE_EXPORT QgsSymbolLayerV2Utils
     static double lineWidthScaleFactor( QgsRenderContext& c, QgsSymbolV2::OutputUnit u );
     /**Returns scale factor painter units -> pixel dimensions*/
     static double pixelSizeScaleFactor( QgsRenderContext& c, QgsSymbolV2::OutputUnit u );
+    /**Creates a render context for a pixel based device*/
+    static QgsRenderContext createRenderContext( QPainter* p );
 };
 
 class QPolygonF;

src/core/symbology-ng/qgssymbolv2.cpp

@@ -160,8 +160,7 @@ QColor QgsSymbolV2::color()
 
 void QgsSymbolV2::drawPreviewIcon( QPainter* painter, QSize size )
 {
-  QgsRenderContext context;
-  context.setPainter( painter );
+  QgsRenderContext context = QgsSymbolLayerV2Utils::createRenderContext( painter );
   QgsSymbolV2RenderContext symbolContext( context, mOutputUnit );
   for ( QgsSymbolLayerV2List::iterator it = mLayers.begin(); it != mLayers.end(); ++it )
   {
@@ -186,9 +185,7 @@ QImage QgsSymbolV2::bigSymbolPreviewImage()
     p.drawLine( 50, 0, 50, 100 );
   }
 
-  QgsRenderContext context;
-  context.setPainter( &p );
-
+  QgsRenderContext context = QgsSymbolLayerV2Utils::createRenderContext( &p );
   startRender( context );
 
   if ( mType == QgsSymbolV2::Line )
@@ -248,7 +245,7 @@ QgsSymbolLayerV2List QgsSymbolV2::cloneLayers() const
 ////////////////////
 
 QgsSymbolV2RenderContext::QgsSymbolV2RenderContext( QgsRenderContext& c, QgsSymbolV2::OutputUnit u )
-  : mRenderContext( c ), mOutputUnit( u )
+    : mRenderContext( c ), mOutputUnit( u )
 {
 
 }
@@ -258,12 +255,12 @@ QgsSymbolV2RenderContext::~QgsSymbolV2RenderContext()
 
 }
 
-double QgsSymbolV2RenderContext::outputLineWidth(double width) const
+double QgsSymbolV2RenderContext::outputLineWidth( double width ) const
 {
   return width * QgsSymbolLayerV2Utils::lineWidthScaleFactor( mRenderContext, mOutputUnit );
 }
 
-double QgsSymbolV2RenderContext::outputPixelSize(double size) const
+double QgsSymbolV2RenderContext::outputPixelSize( double size ) const
 {
   return size * QgsSymbolLayerV2Utils::pixelSizeScaleFactor( mRenderContext, mOutputUnit );
 }