Improve escaping syntax

`#` is now a general escaping character:

- `#[0-9a-fA-F]` changes color
- `##` and `#^` produces literal `#` and `^` respectively
- A `#` not followed by characters above produces a normal `#`

Examples:

- `^3` produces `→`
- `#^3` produces `^3`
- `##^3` produces `#→`
- `###^3` produces `#^3`
- `####^3` produces `##→`
- `^k` and `#^k` both produce `^k` (`^k` is not a valid arrow sequence)
- `##^k` and `###^k` both produce `#^k`
- `####^k` produces `##^k`
- `#1` changes color
- `##1` produces `#1`
- `###1` produces `#`, then changes color
- `####1` produces `##1`
- `#k` and `##k` both produce `#k` (`k` is not a hex digit)
- `##` produces `#`
- `###` and `####` both produce `##`

README.md

@@ -22,7 +22,11 @@ That said, there are some basic text formatting options:
 
   Writing "^" followed by a letter "a" through "h" will produce double-wide versions of these arrows, in the same order.  These wide arrows occupy 0x89 to 0x91 in the character set.
 
-* A color may be specified in the sign text by using "#" followed by a single hexadcimal digit (0-9 or a-f).  These colors come from the standard Linux/IRC/CGA color set, and are shown in the sign's formspec.  Any color change will remain in effect until changed again, or until the next line break.  Any number of color changes in any arbitrary arrangement is allowed. To write "#" on a sign, write "##".
+  To write a "^" on a sign, wirte "#^"
+
+* A color may be specified in the sign text by using "#" followed by a single hexadcimal digit (0-9 or a-f).  These colors come from the standard Linux/IRC/CGA color set, and are shown in the sign's formspec.  Any color change will remain in effect until changed again, or until the next line break.  Any number of color changes in any arbitrary arrangement is allowed.
+
+  To write "#" on a sign, write "##".
 
 * Most writable signs can display double-wide text by flipping a switch in the sign's formspec.
 

api.lua

@@ -513,31 +513,37 @@ local function make_line_texture(line, lineno, pos, line_width, line_height, cwi
 	for word_i, word in ipairs(line) do
 		local chars = { }
 		local ch_offs = 0
-		word = string.gsub(word, "%^[12345678abcdefgh]", {
-			["^1"] = string.char(0x81),
-			["^2"] = string.char(0x82),
-			["^3"] = string.char(0x83),
-			["^4"] = string.char(0x84),
-			["^5"] = string.char(0x85),
-			["^6"] = string.char(0x86),
-			["^7"] = string.char(0x87),
-			["^8"] = string.char(0x88),
-			["^a"] = string.char(0x8a),
-			["^b"] = string.char(0x8b),
-			["^c"] = string.char(0x8c),
-			["^d"] = string.char(0x8d),
-			["^e"] = string.char(0x8e),
-			["^f"] = string.char(0x8f),
-			["^g"] = string.char(0x90),
-			["^h"] = string.char(0x91)
-		})
 		local word_l = #word
 		local i = 1
+		local escape = 0
 		while i <= word_l  do
 			local wide_type, wide_c = string.match(word:sub(i), "^&#([xu])(%x+);")
 			local c = word:sub(i, i)
 			local c2 = word:sub(i+1, i+1)
 
+			if escape > 0 then escape = escape - 1 end
+			if c == "^" and escape == 0 and c2:find("[1-8a-h]") then
+				c = ({
+					["1"] = string.char(0x81),
+					["2"] = string.char(0x82),
+					["3"] = string.char(0x83),
+					["4"] = string.char(0x84),
+					["5"] = string.char(0x85),
+					["6"] = string.char(0x86),
+					["7"] = string.char(0x87),
+					["8"] = string.char(0x88),
+					["a"] = string.char(0x8a),
+					["b"] = string.char(0x8b),
+					["c"] = string.char(0x8c),
+					["d"] = string.char(0x8d),
+					["e"] = string.char(0x8e),
+					["f"] = string.char(0x8f),
+					["g"] = string.char(0x90),
+					["h"] = string.char(0x91)
+				})[c2]
+				i = i + 1
+			end
+
 			local wide_skip = 0
 			if force_unicode_font then
 				if wide_c then
@@ -562,11 +568,12 @@ local function make_line_texture(line, lineno, pos, line_width, line_height, cwi
 				wide_skip = #wide_c + 3
 			end
 
-			if c == "#" and c2 ~= "#" then
-				local cc = tonumber(c2, 16)
-				if cc then
+			if c == "#" and escape == 0 and c2:find("[0-9A-Fa-f#^]") then
+				if c2 == "#" or c2 == "^" then
+					escape = 2
+				else
 					i = i + 1
-					cur_color = cc
+					cur_color = tonumber(c2, 16)
 				end
 			elseif wide_c then
 				local w, code
@@ -754,7 +761,9 @@ local function make_infotext(text)
 	local lines = signs_lib.split_lines_and_words(text) or {}
 	local lines2 = { }
 	for _, line in ipairs(lines) do
-		table.insert(lines2, (table.concat(line, " "):gsub("#[0-9a-fA-F]", ""):gsub("##", "#")))
+		table.insert(lines2, (table.concat(line, " "):gsub("#[0-9a-fA-F#^]", function (s)
+			return s:sub(2):find("[#^]") and s:sub(2) or ""
+		end)))
 	end
 	return table.concat(lines2, "\n")
 end