Add an [invert:<mode> texture modifier

Inverts the given channels of the base image.
Mode may contain the characters "r", "g", "b", "a".
Only the channels that are mentioned in the mode string will be inverted.

2 files changed, 50 insertions, 2 deletions

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index aa4f129f0..41e7c00eb 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -318,6 +318,15 @@ Example:
 
     default_sandstone.png^[opacity:127
 
+#### `[invert:<mode>`
+Inverts the given channels of the base image.
+Mode may contain the characters "r", "g", "b", "a".
+Only the channels that are mentioned in the mode string will be inverted.
+
+Example:
+
+	default_apple.png^[invert:rgb
+
 #### `[brighten`
 Brightens the texture.
 
diff --git a/src/client/tile.cpp b/src/client/tile.cpp
index 67d5d8d1a..8f0c39465 100644
--- a/src/client/tile.cpp
+++ b/src/client/tile.cpp
@@ -1783,9 +1783,48 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 			for (u32 y = 0; y < dim.Height; y++)
 			for (u32 x = 0; x < dim.Width; x++)
 			{
-				video::SColor c = baseimg->getPixel(x,y);
+				video::SColor c = baseimg->getPixel(x, y);
 				c.setAlpha(floor((c.getAlpha() * ratio) / 255 + 0.5));
-				baseimg->setPixel(x,y,c);
+				baseimg->setPixel(x, y, c);
+			}
+		}
+		/*
+			[invert:mode
+			Inverts the given channels of the base image.
+			Mode may contain the characters "r", "g", "b", "a".
+			Only the channels that are mentioned in the mode string
+			will be inverted.
+		*/
+		else if (str_starts_with(part_of_name, "[invert:")) {
+			if (baseimg == NULL) {
+				errorstream << "generateImagePart(): baseimg == NULL "
+						<< "for part_of_name=\"" << part_of_name
+						<< "\", cancelling." << std::endl;
+				return false;
+			}
+
+			Strfnd sf(part_of_name);
+			sf.next(":");
+
+			std::string mode = sf.next("");
+			u32 mask = 0;
+			if (mode.find("a") != std::string::npos)
+				mask |= 0xff000000UL;
+			if (mode.find("r") != std::string::npos)
+				mask |= 0x00ff0000UL;
+			if (mode.find("g") != std::string::npos)
+				mask |= 0x0000ff00UL;
+			if (mode.find("b") != std::string::npos)
+				mask |= 0x000000ffUL;
+
+			core::dimension2d<u32> dim = baseimg->getDimension();
+
+			for (u32 y = 0; y < dim.Height; y++)
+			for (u32 x = 0; x < dim.Width; x++)
+			{
+				video::SColor c = baseimg->getPixel(x, y);
+				c.color ^= mask;	
+				baseimg->setPixel(x, y, c);
 			}
 		}
 		else