Added "[sheet" to the texture special commands.

"[sheet:WxH:X,Y" assumes the base image is a tilesheet with W*H tiles
on it and crops to the tile at position X,Y.  Basically it works
like "[verticalframe" but in 2D.

For testing, I combined the four default_chest images into one.

doc/lua_api.txt

@@ -403,6 +403,11 @@ Apply a mask to the base image.
 
 The mask is applied using binary AND.
 
+#### `[sheet:<w>x<h>:<x>,<y>`
+Retrieves a tile at position x,y from the base image
+which it assumes to be a tilesheet with dimensions w,h.
+
+
 #### `[colorize:<color>:<ratio>`
 Colorize the textures with the given color.
 `<color>` is specified as a `ColorString`.

games/minimal/mods/default/init.lua

@@ -1130,8 +1130,9 @@ minetest.register_node("default:sign_wall", {
 
 minetest.register_node("default:chest", {
 	description = "Chest",
-	tiles ={"default_chest_top.png", "default_chest_top.png", "default_chest_side.png",
+	tiles ={"default_chest.png^[sheet:2x2:0,0", "default_chest.png^[sheet:2x2:0,0",
-		"default_chest_side.png", "default_chest_side.png", "default_chest_front.png"},
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:1,0",
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:0,1"},
 	paramtype2 = "facedir",
 	groups = {snappy=2,choppy=2,oddly_breakable_by_hand=2},
 	legacy_facedir_simple = true,
@@ -1164,8 +1165,9 @@ end
 
 minetest.register_node("default:chest_locked", {
 	description = "Locked Chest",
-	tiles ={"default_chest_top.png", "default_chest_top.png", "default_chest_side.png",
+	tiles ={"default_chest.png^[sheet:2x2:0,0", "default_chest.png^[sheet:2x2:0,0",
-		"default_chest_side.png", "default_chest_side.png", "default_chest_lock.png"},
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:1,0",
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:1,1"},
 	paramtype2 = "facedir",
 	groups = {snappy=2,choppy=2,oddly_breakable_by_hand=2},
 	legacy_facedir_simple = true,

src/client/tile.cpp

@@ -1827,6 +1827,49 @@ bool TextureSource::generateImagePart(std::string part_of_name,
 				baseimg->setPixel(x, y, c);
 			}
 		}
+		/*
+			[sheet:WxH:X,Y
+			Retrieves a tile at position X,Y (in tiles)
+			from the base image it assumes to be a
+			tilesheet with dimensions W,H (in tiles).
+		*/
+		else if (part_of_name.substr(0,7) == "[sheet:") {
+			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(":");
+			u32 w0 = stoi(sf.next("x"));
+			u32 h0 = stoi(sf.next(":"));
+			u32 x0 = stoi(sf.next(","));
+			u32 y0 = stoi(sf.next(":"));
+
+			core::dimension2d<u32> img_dim = baseimg->getDimension();
+			core::dimension2d<u32> tile_dim(v2u32(img_dim) / v2u32(w0, h0));
+
+			video::IImage *img = driver->createImage(
+					video::ECF_A8R8G8B8, tile_dim);
+			if (!img) {
+				errorstream << "generateImagePart(): Could not create image "
+						<< "for part_of_name=\"" << part_of_name
+						<< "\", cancelling." << std::endl;
+				return false;
+			}
+
+			img->fill(video::SColor(0,0,0,0));
+			v2u32 vdim(tile_dim);
+			core::rect<s32> rect(v2s32(x0 * vdim.X, y0 * vdim.Y), tile_dim);
+			baseimg->copyToWithAlpha(img, v2s32(0), rect,
+					video::SColor(255,255,255,255), NULL);
+
+			// Replace baseimg
+			baseimg->drop();
+			baseimg = img;
+		}
 		else
 		{
 			errorstream << "generateImagePart(): Invalid "