Add an elementary decoder for Xcursor files

plugins/xcursor.lua

@@ -0,0 +1,54 @@
+--
+-- xcursor.lua: X11 cursors
+--
+-- Copyright (c) 2021, Přemysl Eric Janouch <p@janouch.name>
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+-- MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+-- SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+-- WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+-- OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+-- CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+--
+
+local detect = function (c)
+	return c:read (4) == "Xcur"
+end
+
+-- https://www.x.org/releases/current/doc/man/man3/Xcursor.3.xhtml
+local decode = function (c)
+	if not detect (c) then error ("not an Xcursor file") end
+
+	-- libXcursor shows that they are always little-endian
+	c (1, 4):mark ("Xcursor magic")
+	c.endianity = "le"
+
+	local size = c:u32 ("header size: %d")
+	-- TODO: check the version, although it is essentially set in stone
+	--   as 1.0.0, with X.org being a nearly abandoned project
+	local version = c:u32 ("file version: %s", function (u32)
+		return "%d.%d.%d", u32 >> 16, (u32 >> 8) & 255, u32 & 255
+	end)
+	local ntoc = c:u32 ("number of ToC entries: %d")
+
+	local i
+	for i = 1, ntoc do
+		local start = c.position
+		local type = c:u32 ("entry type: %s", function (u32)
+			if u32 == 0xfffe0001 then return "comment" end
+			if u32 == 0xfffd0002 then return "image" end
+			return "unknown: %d", u32
+		end)
+		local subtype = c:u32 ("entry subtype: %d")
+		local position = c:u32 ("chunk position: %d")
+		c (start, c.position - 1):mark (("ToC entry %d"):format (i))
+	end
+
+	-- TODO: decode all entries as well
+end
+
+hex.register { type="xcursor", detect=detect, decode=decode }