Add formspec toolkit and refactor mainmenu to use it

Fix crash on using cursor keys in client menu without selected server
Add support for non fixed size tabviews

builtin/fstk/ui.lua

@@ -0,0 +1,172 @@
+--Minetest
+--Copyright (C) 2014 sapier
+--
+--self program is free software; you can redistribute it and/or modify
+--it under the terms of the GNU Lesser General Public License as published by
+--the Free Software Foundation; either version 2.1 of the License, or
+--(at your option) any later version.
+--
+--self program is distributed in the hope that it will be useful,
+--but WITHOUT ANY WARRANTY; without even the implied warranty of
+--MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--GNU Lesser General Public License for more details.
+--
+--You should have received a copy of the GNU Lesser General Public License along
+--with self program; if not, write to the Free Software Foundation, Inc.,
+--51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+ui = {}
+ui.childlist = {}
+ui.default = nil
+
+--------------------------------------------------------------------------------
+function ui.add(child)
+	--TODO check child
+	ui.childlist[child.name] = child
+	
+	return child.name
+end
+
+--------------------------------------------------------------------------------
+function ui.delete(child)
+
+	if ui.childlist[child.name] == nil then
+		return false
+	end
+	
+	ui.childlist[child.name] = nil
+	return true
+end
+
+--------------------------------------------------------------------------------
+function ui.set_default(name)
+	ui.default = name
+end
+
+--------------------------------------------------------------------------------
+function ui.find_by_name(name)
+	return ui.childlist[name]
+end
+
+--------------------------------------------------------------------------------
+--------------------------------------------------------------------------------
+-- Internal functions not to be called from user
+--------------------------------------------------------------------------------
+--------------------------------------------------------------------------------
+
+--------------------------------------------------------------------------------
+function ui.update()
+	local formspec = ""
+
+	-- handle errors
+	if gamedata ~= nil and gamedata.errormessage ~= nil then
+		formspec = "size[12,3.2]" ..
+			"textarea[1,1;10,2;;ERROR: " ..
+			core.formspec_escape(gamedata.errormessage) ..
+			";]"..
+			"button[4.5,2.5;3,0.5;btn_error_confirm;" .. fgettext("Ok") .. "]"
+	else
+		local active_toplevel_ui_elements = 0
+		for key,value in pairs(ui.childlist) do
+			if (value.type == "toplevel") then
+				local retval = value:get_formspec()
+
+				if retval ~= nil and retval ~= "" then
+					active_toplevel_ui_elements = active_toplevel_ui_elements +1
+					formspec = formspec .. retval
+				end
+			end
+		end
+		
+		-- no need to show addons if there ain't a toplevel element
+		if (active_toplevel_ui_elements > 0) then
+			for key,value in pairs(ui.childlist) do
+				if (value.type == "addon") then
+					local retval = value:get_formspec()
+
+					if retval ~= nil and retval ~= "" then
+						formspec = formspec .. retval
+					end
+				end
+			end
+		end
+
+		if (active_toplevel_ui_elements > 1) then
+			print("WARNING: ui manager detected more then one active ui element, self most likely isn't intended")
+		end
+
+		if (active_toplevel_ui_elements == 0) then
+			print("WARNING: not a single toplevel ui element active switching to default")
+			ui.childlist[ui.default]:show()
+			formspec = ui.childlist[ui.default]:get_formspec()
+		end
+	end
+	core.update_formspec(formspec)
+end
+
+--------------------------------------------------------------------------------
+function ui.handle_buttons(fields)
+
+	if fields["btn_error_confirm"] then
+		gamedata.errormessage = nil
+		update_menu()
+		return
+	end
+
+	for key,value in pairs(ui.childlist) do
+
+		local retval = value:handle_buttons(fields)
+
+		if retval then
+			ui.update()
+			return
+		end
+	end
+end
+
+
+--------------------------------------------------------------------------------
+function ui.handle_events(event)
+	
+	for key,value in pairs(ui.childlist) do
+
+		if value.handle_events ~= nil then
+			local retval = value:handle_events(event)
+
+			if retval then
+				print("event handled by: " .. key)
+				return retval
+			end
+		end
+	end
+end
+
+--------------------------------------------------------------------------------
+--------------------------------------------------------------------------------
+-- initialize callbacks
+--------------------------------------------------------------------------------
+--------------------------------------------------------------------------------
+core.button_handler = function(fields)
+	if fields["btn_error_confirm"] then
+		gamedata.errormessage = nil
+		ui.update()
+		return
+	end
+
+	if ui.handle_buttons(fields) then
+		ui.update()
+	end
+end
+
+--------------------------------------------------------------------------------
+core.event_handler = function(event)
+	if ui.handle_events(event) then
+		ui.update()
+		return
+	end
+
+	if event == "Refresh" then
+		ui.update()
+		return
+	end
+end