Added 'combine' option to ColorStyle.

doc/type/style.txt

@@ -142,6 +142,7 @@ The rest of the properties depend on the type of [[type:field]] this style is fo
 | ^^^		@top width@	^^^			^^^	^^^
 | ^^^		@bottom width@	^^^			^^^	^^^
 | ^^^		@mask@	[[type:scriptable]] [[type:filename]]	''none''	A mask to apply to the box, black areas in the mask become transparent.
+| ^^^		@combine@	[[type:combine]]		@"normal"@	How to combine the color with the background? Only applies when a mask is used.
 	
 !	<<<	<<<	<<<	<<<
 | @"image"@	@mask@		[[type:scriptable]] [[type:filename]]	''none''	A mask to apply to the image, black areas in the mask become transparent, similair to [[fun:set_mask]].

src/data/field/color.cpp

@@ -52,6 +52,7 @@ ColorStyle::ColorStyle(const ColorFieldP& field)
 	, radius(0)
 	, left_width(100000), right_width (100000)
 	, top_width (100000), bottom_width(100000)
+	, combine(COMBINE_NORMAL)
 {}
 
 IMPLEMENT_REFLECTION(ColorStyle) {
@@ -62,6 +63,7 @@ IMPLEMENT_REFLECTION(ColorStyle) {
 	REFLECT(top_width);
 	REFLECT(bottom_width);
 	REFLECT_N("mask", mask_filename);
+	REFLECT(combine);
 }
 
 int ColorStyle::update(Context& ctx) {

src/data/field/color.hpp

@@ -62,6 +62,7 @@ class ColorStyle : public Style {
 	double             top_width;       ///< Width of the colored region on the top side
 	double             bottom_width;    ///< Width of the colored region on the bottom side
 	Scriptable<String> mask_filename;   ///< Filename of an additional mask over the images
+	Scriptable<ImageCombine> combine;   ///< How to combine image with the background
 	
 	virtual int update(Context&);
 };

src/render/value/color.cpp

@@ -48,7 +48,7 @@ void ColorValueViewer::draw(RotatedDC& dc) {
 			Image img(alpha_mask->size.x, alpha_mask->size.y);
 			fill_image(img, value().value());
 			alpha_mask->setAlpha(img);
-			dc.DrawImage(img, RealPoint(0,0));
+			dc.DrawImage(img, RealPoint(0,0), style().combine);
 		} else {
 			// do we need clipping?
 			bool clip = style().left_width < style().width  && style().right_width  < style().width &&