ImagePathWML: added ~NEG() (negative) function

src/image_modifications.cpp

@@ -205,6 +205,11 @@ surface sepia_modification::operator()(const surface &src) const
 	return sepia_image(src);
 }
 
+surface negative_modification::operator()(const surface &src) const
+{
+	return negative_image(src);
+}
+
 surface plot_alpha_modification::operator()(const surface& src) const
 {
 	return alpha_to_greyscale(src);
@@ -755,6 +760,12 @@ REGISTER_MOD_PARSER(SEPIA, )
 	return new sepia_modification;
 }
 
+// Negative
+REGISTER_MOD_PARSER(NEG, )
+{
+	return new negative_modification;
+}
+
 // Plot Alpha
 REGISTER_MOD_PARSER(PLOT_ALPHA, )
 {

src/image_modifications.hpp

@@ -229,6 +229,14 @@ struct sepia_modification : modification
 	virtual surface operator()(const surface &src) const;
 };
 
+/**
+ * Make an image negative (NEG)
+ */
+struct negative_modification : modification
+{
+	virtual surface operator()(const surface &src) const;
+};
+
 /**
  * Plot Alpha (Alpha) modification
  */

src/sdl/utils.cpp

@@ -1031,6 +1031,43 @@ surface sepia_image(const surface &surf, bool optimize)
 	return optimize ? create_optimized_surface(nsurf) : nsurf;
 }
 
+surface negative_image(const surface &surf, bool optimize)
+{
+	if(surf == NULL)
+		return NULL;
+
+	surface nsurf(make_neutral_surface(surf));
+	if(nsurf == NULL) {
+		std::cerr << "failed to make neutral surface\n";
+		return NULL;
+	}
+
+	{
+		surface_lock lock(nsurf);
+		Uint32* beg = lock.pixels();
+		Uint32* end = beg + nsurf->w*surf->h;
+
+		while(beg != end) {
+			Uint8 alpha = (*beg) >> 24;
+
+			if(alpha) {
+				Uint8 r, g, b;
+				r = (*beg) >> 16;
+				g = (*beg) >> 8;
+				b = (*beg);
+
+				// basically, to get a channel's negative it's enough
+				// to subtract its value from 255
+				*beg = (alpha << 24) | ((255 - r) << 16) | ((255 - g) << 8) | (255 - b);
+			}
+
+			++beg;
+		}
+	}
+
+	return optimize ? create_optimized_surface(nsurf) : nsurf;
+}
+
 surface alpha_to_greyscale(const surface &surf, bool optimize)
 {
 	if(surf == NULL)

src/sdl/utils.hpp

@@ -247,6 +247,7 @@ surface tile_surface(const surface &surf, int w, int h, bool optimize=true);
 surface adjust_surface_color(const surface &surf, int r, int g, int b, bool optimize=true);
 surface greyscale_image(const surface &surf, bool optimize=true);
 surface sepia_image(const surface &surf, bool optimize=true);
+surface negative_image(const surface &surf, bool optimize=true);
 surface alpha_to_greyscale(const surface & surf, bool optimize=true);
 surface wipe_alpha(const surface & surf, bool optimize=true);
 /** create an heavy shadow of the image, by blurring, increasing alpha and darkening */