ImagePathWML: added BW() (black and white) function

Partial merge of PR #394

changelog

@@ -12,6 +12,8 @@ Version 1.13.0+dev:
    * Fixed the Shuja not having the default AMLA.
  * WML engine:
    * Added support for [object] duration=turn end
+   * New image path functions:
+      * ~BW(): converts an image to black and white
  * Miscellaneous and bug fixes:
    * Removed abandoned libana network API implementation.
    * Fixed bug#23201 Toggle icons display error in replay.

src/image_modifications.cpp

@@ -200,6 +200,11 @@ surface gs_modification::operator()(const surface& src) const
 	return greyscale_image(src);
 }
 
+surface bw_modification::operator()(const surface& src) const
+{
+	return monochrome_image(src, threshold_);
+}
+
 surface sepia_modification::operator()(const surface &src) const
 {
 	return sepia_image(src);
@@ -750,6 +755,32 @@ REGISTER_MOD_PARSER(GS, )
 	return new gs_modification;
 }
 
+// Black and white
+REGISTER_MOD_PARSER(BW, args)
+{
+	const std::vector<std::string>& params = utils::split(args, ',');
+	if (params.size() == 1) {
+		try {
+			int threshold = lexical_cast<int>(params[0]);
+			if (threshold < 0 || threshold > 255) {
+				ERR_DP << "~BW() argument out of range 0 - 255" << std::endl;
+				return NULL;
+			}
+			else {
+				return new bw_modification(threshold);
+			}
+		}
+		catch (bad_lexical_cast) {
+			ERR_DP << "unsupported argument in ~BW() function" << std::endl;
+			return NULL;
+		}
+	}
+	else {
+		ERR_DP << "~BW() requires  exactly one argument" << std::endl;
+		return NULL;
+	}
+}
+
 // Sepia
 REGISTER_MOD_PARSER(SEPIA, )
 {

src/image_modifications.hpp

@@ -221,6 +221,18 @@ public:
 	virtual surface operator()(const surface& src) const;
 };
 
+/**
+ * Black and white (BW) modification.
+ */
+class bw_modification : public modification
+{
+public:
+	bw_modification(int threshold): threshold_(threshold) {}
+	virtual surface operator()(const surface& src) const;
+private:
+	int threshold_;
+};
+
 /**
  * Give to the image a sepia tint (SEPIA)
  */

src/sdl/utils.cpp

@@ -989,6 +989,46 @@ surface greyscale_image(const surface &surf, bool optimize)
 	return optimize ? create_optimized_surface(nsurf) : nsurf;
 }
 
+surface monochrome_image(const surface &surf, const int threshold, 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, result;
+				r = (*beg) >> 16;
+				g = (*beg) >> 8;
+				b = (*beg);
+
+				// first convert the pixel to grayscale
+				// if the resulting value is above the threshold make it black
+				// else make it white
+				result = static_cast<Uint8>(0.299 * r + 0.587 * g + 0.114 * b) > threshold ? 255 : 0;
+
+				*beg = (alpha << 24) | (result << 16) | (result << 8) | result;
+			}
+
+			++beg;
+		}
+	}
+
+	return optimize ? create_optimized_surface(nsurf) : nsurf;
+}
+
 surface sepia_image(const surface &surf, bool optimize)
 {
 	if(surf == NULL)

src/sdl/utils.hpp

@@ -246,6 +246,7 @@ 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 monochrome_image(const surface &surf, const int threshold, 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);