Handle ingredient quantities in craft guide

Alloy cooking recipes have quantities for the ingredients, which need to
be shown.  The buttons on which the ingredients are shown don't natively
support showing an item count, so hack it up with the label facility.
Also, the button names, supporting clicking to see recipes recursively,
need to be based only on the item name part of the ingredient, dropping
the quantity part.

callbacks.lua

@@ -123,12 +123,12 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 	for name, value in pairs(fields) do
 		if string.sub(name, 1, 12) == "item_button_" then
 			clicked_item = string.sub(name, 13)
+			if string.sub(clicked_item, 1, 6) == "group:" then
+				minetest.sound_play("click", {to_player=player_name, gain = 0.1})
+				unified_inventory.apply_filter(player, clicked_item)
+				return
+			end
 			break
-		elseif string.sub(name, 1, 11) == "item_group_" then
-			minetest.sound_play("click",
-					{to_player=player_name, gain = 0.1})
-			unified_inventory.apply_filter(player, "group:"..string.sub(name, 12))
-			return
 		end
 	end
 	if clicked_item then

register.lua

@@ -134,6 +134,39 @@ unified_inventory.register_page("craft", {
 	end,
 })
 
+-- stack_image_button(): generate a form button displaying a stack of items
+--
+-- Normally a simple item_image_button[] is used.  If the stack contains
+-- more than one item, item_image_button[] doesn't have an option to
+-- display an item count in the way that an inventory slot does, so
+-- we have to fake it using the label facility.  This doesn't let us
+-- specify that the count should appear at bottom right, so we use some
+-- dodgy whitespace to shift it away from the centre of the button.
+-- Unfortunately the correct amount of whitespace depends on display
+-- resolution, so the results from this will be variable.  This should be
+-- replaced as soon as the engine adds support for a proper item count,
+-- or at least label placement control, on buttons.
+--
+-- The specified item may be a group.  In that case, an image_button[]
+-- is used, displaying an image that just indicates grouping, with a
+-- label giving the name of the specific group.  It very often happens
+-- that the group name doesn't fit within the confines of the button and
+-- gets cropped.  Group names are also not brilliantly readable against
+-- the background of the group image.
+local function stack_image_button(x, y, w, h, buttonname_prefix, stackstring)
+	local st = ItemStack(stackstring)
+	local n = st:get_name()
+	local c = st:get_count()
+	local clab = c == 1 and "" or string.format("%9d", c)
+	local buttonname = buttonname_prefix..n
+	local xywh = x..","..y..";"..w..","..h
+	if string.sub(n, 1, 6) == "group:" then
+		return "image_button["..xywh..";".."ui_group.png;"..minetest.formspec_escape(buttonname)..";"..minetest.formspec_escape(string.sub(n, 7)).."\n\n"..clab.."]"
+	else
+		return "item_image_button["..xywh..";"..minetest.formspec_escape(n)..";"..minetest.formspec_escape(buttonname_prefix..n)..";\n\n"..clab.."]"
+	end
+end
+
 unified_inventory.register_page("craftguide", {
 	get_formspec = function(player)
 		local player_name = player:get_player_name()
@@ -188,20 +221,7 @@ unified_inventory.register_page("craftguide", {
 		for x = 1, width do
 			local item = craft.items[i]
 			if item then
-				if string.sub(item, 1, 6) == "group:" then
+				formspec = formspec..stack_image_button(1.0+x, 0.0+y, 1.1, 1.1, "item_button_", item)
-					local group = string.sub(item, 7)
-					formspec = formspec.."image_button["
-						..(1.0 + x)..","..(0.0 + y)..";1.1,1.1;"
-						.."ui_group.png;"
-						.."item_group_"..minetest.formspec_escape(group)..";"
-						..minetest.formspec_escape(group).."]"
-				else
-					formspec = formspec.."item_image_button["
-						..(1.0 + x)..","..(0.0 + y)..";1.1,1.1;"
-						..minetest.formspec_escape(item)..";"
-						.."item_button_"
-						..minetest.formspec_escape(item)..";]"
-				end
 			end
 			i = i + 1
 		end