Use 9-slicing to build inventory-type backgrounds

This way the slots are all nice and crisp regardless of GUI scale or
image size, and we only need the single slot and its bright version.

This also makes the standard crafting grid into a style table entry that
can be referenced to insert the crafting grid at its proper
style-specific position in any formspec.

And it also makes the craft grid arrow, its X position, and the crafting
grid's result slot X position into style table entries.

Includes a few public helper functions to do most of the work:

`ui.single_slot(xpos, ypos, bright)`

    Does just what it sounds like: it returns a single slot image.
    `xpos` and `ypos` are normal coordinates in slots, as you'd use in
    `image[]` element.  `bright` is a flag that switches to the brighter
    version of the slot image.

`ui.make_trash_slot(xpos, ypos)`

    Creates a single slot, with a one-item `list[]` and a trash can icon
    overlay.

`ui.make_inv_img_grid(xpos, ypos, width, height, bright)`

    Generates a `width` by `height` grid of slot images, using the
    single_slot function above, starting at (`xpos`,`ypos`) for the
    top-left.  Position is as in any `image[]` element, and dimensions
    are in integer numbers of slots (so 8,4 would be a standard inventory).
    `bright` is as above.

All three return a string that can be directly inserted into a formspec.

api.lua

@@ -303,8 +303,31 @@ function ui.register_button(name, def)
 	table.insert(ui.buttons, def)
 end
 
-
 function ui.is_creative(playername)
 	return minetest.check_player_privs(playername, {creative=true})
 		or minetest.settings:get_bool("creative_mode")
 end
+
+function ui.single_slot(xpos, ypos, bright)
+	return string.format("background9[%f,%f;%f,%f;ui_single_slot%s.png;false;16]",
+	xpos, ypos, ui.imgscale, ui.imgscale, (bright and "_bright" or "") )
+end
+
+function ui.make_trash_slot(xpos, ypos)
+	return
+		ui.single_slot(xpos, ypos)..
+		"image["..xpos..","..ypos..";1.25,1.25;ui_trash_slot_icon.png^[opacity:95]"..
+		"list[detached:trash;main;"..xpos..","..ypos..";1,1;]"
+end
+
+function ui.make_inv_img_grid(xpos, ypos, width, height, bright)
+	local tiled = {}
+	local n=1
+	for y = 0, (height - 1) do
+		for x = 0, (width -1) do
+			tiled[n] = ui.single_slot(xpos + (ui.imgscale * x), ypos + (ui.imgscale * y), bright)
+			n = n + 1
+		end
+	end
+	return table.concat(tiled)
+end

bags.lua

@@ -8,14 +8,16 @@ License: GPLv3
 local S = minetest.get_translator("unified_inventory")
 local F = minetest.formspec_escape
 local ui = unified_inventory
-local bags_inv_bg = "image[0.3,1.5;"..(ui.imgscale*8)..",%f;%s]"
 
 ui.register_page("bags", {
 	get_formspec = function(player)
 		local player_name = player:get_player_name()
 		return { formspec = table.concat({
 			ui.style_full.standard_inv_bg,
-			string.format(bags_inv_bg, ui.imgscale, "ui_bags_header.png"),
+			ui.single_slot(0.925, 1.5),
+			ui.single_slot(3.425, 1.5),
+			ui.single_slot(5.925, 1.5),
+			ui.single_slot(8.425, 1.5),
 			"label["..ui.style_full.form_header_x..","..ui.style_full.form_header_y..";" .. F(S("Bags")) .. "]",
 			"button[0.6125,2.75;1.875,0.75;bag1;" .. F(S("Bag @1", 1)) .. "]",
 			"button[3.1125,2.75;1.875,0.75;bag2;" .. F(S("Bag @1", 2)) .. "]",
@@ -49,34 +51,27 @@ for bag_i = 1, 4 do
 		get_formspec = function(player)
 			local stack = get_player_bag_stack(player, bag_i)
 			local image = stack:get_definition().inventory_image
+			local slots = stack:get_definition().groups.bagslots
+
 			local formspec = {
 				ui.style_full.standard_inv_bg,
+				ui.make_inv_img_grid(0.3, 1.5, 8, slots/8),
 				"image[9.2,0.4;1,1;" .. image .. "]",
 				"label[0.3,0.65;" .. F(S("Bag @1", bag_i)) .. "]",
 				"listcolors[#00000000;#00000000]",
 				"listring[current_player;main]",
+				string.format("list[current_player;bag%icontents;%f,%f;8,3;]",
+				    bag_i, 0.3 + ui.list_img_offset, 1.5 + ui.list_img_offset),
+				"listring[current_name;bag" .. bag_i .. "contents]",
 			}
-			local n = 6
-
-			local slots = stack:get_definition().groups.bagslots
-			if slots == 8 then
-					formspec[n] = string.format(bags_inv_bg, ui.imgscale, "ui_bags_inv_small.png")
-			elseif slots == 16 then
-					formspec[n] = string.format(bags_inv_bg, ui.imgscale*2, "ui_bags_inv_medium.png")
-			elseif slots == 24 then
-					formspec[n] = string.format(bags_inv_bg, ui.imgscale*3, "ui_bags_inv_large.png")
-			end
-			formspec[n+1] = "list[current_player;bag" .. bag_i .. "contents;0.45,1.65;8,3;]"
-			formspec[n+2] = "listring[current_name;bag" .. bag_i .. "contents]"
-			n = n + 3
+			local n = #formspec + 1
 
 			local player_name = player:get_player_name() -- For if statement.
 			if ui.trash_enabled
 				or ui.is_creative(player_name)
 				or minetest.get_player_privs(player_name).give then
-					formspec[n] = "image[7.8,0.25;"..ui.trash_slot_img.."]"
-					formspec[n+1] = "list[detached:trash;main;7.95,0.25;1,1;]"
-				n = n + 2
+					formspec[n] = ui.make_trash_slot(7.8, 0.25)
+					n = n + 1
 			end
 			local inv = player:get_inventory()
 			for i = 1, 4 do

init.lua

@@ -36,6 +36,7 @@ unified_inventory = {
 	-- Trash enabled
 	trash_enabled = (minetest.settings:get_bool("unified_inventory_trash") ~= false),
 	imgscale = 1.25,
+	list_img_offset = 0.13,
 	standard_background = "background9[0,0;1,1;ui_formbg_9_sliced.png;true;16]",
 }
 
@@ -92,19 +93,31 @@ ui.style_lite = {
 	std_inv_y = 4.6,
 }
 
+dofile(modpath.."/api.lua")
+
 for _, style in ipairs({ui.style_full, ui.style_lite}) do
 	style.items_per_page =  style.pagecols * style.pagerows
 	style.standard_inv =    string.format("list[current_player;main;%f,%f;8,4;]",
-                              style.std_inv_x+0.15, style.std_inv_y+0.15)
+                              style.std_inv_x+0.13, style.std_inv_y+0.13)
 
-	style.standard_inv_bg = string.format("image[%f,%f;%f,%f;ui_main_inventory.png]",
-                              style.std_inv_x, style.std_inv_y,
-                              ui.imgscale*8, ui.imgscale*4)
+	style.standard_inv_bg = ui.make_inv_img_grid(style.std_inv_x, style.std_inv_y, 8, 1, true)..
+	                        ui.make_inv_img_grid(style.std_inv_x, style.std_inv_y + ui.imgscale, 8, 3)
+
+	style.craftarrow_x =    style.craft_x + 3.75
+	style.craftarrow =      string.format("image[%f,%f;%f,%f;ui_crafting_arrow.png]",
+	                            style.craftarrow_x, style.craft_y, ui.imgscale, ui.imgscale)
+	style.craftresult_x =   style.craft_x + 5
+	style.craft_grid =      table.concat({
+	                            ui.make_inv_img_grid(style.craft_x, style.craft_y, 3, 3),
+	                            ui.single_slot(style.craft_x + ui.imgscale*4, style.craft_y), -- the craft result slot
+	                            style.craftarrow,
+	                            string.format("list[current_player;craft;%f,%f;3,3;]",
+                                    style.craft_x + ui.list_img_offset, style.craft_y + ui.list_img_offset),
+	                            string.format("list[current_player;craftpreview;%f,%f;1,1;]",
+                                    style.craftresult_x + ui.list_img_offset, style.craft_y + ui.list_img_offset)
+	                        })
 end
 
-ui.trash_slot_img =         string.format("%f,%f;ui_single_slot.png^(ui_trash_slot_icon.png^[opacity:95)",
-                              ui.imgscale, ui.imgscale)
-
 -- Disable default creative inventory
 local creative = rawget(_G, "creative") or rawget(_G, "creative_inventory")
 if creative then
@@ -120,7 +133,6 @@ if sfinv then
 end
 
 dofile(modpath.."/group.lua")
-dofile(modpath.."/api.lua")
 dofile(modpath.."/internal.lua")
 dofile(modpath.."/callbacks.lua")
 dofile(modpath.."/match_craft.lua")

register.lua

@@ -174,12 +174,10 @@ ui.register_page("craft", {
 
 		local player_name = player:get_player_name()
 		local formspec = {
-			string.format("image[%f,%f;%f,%f;ui_crafting_form.png]", craftx, crafty, ui.imgscale*6, ui.imgscale*3),
 			perplayer_formspec.standard_inv_bg,
+			perplayer_formspec.craft_grid,
 			"label["..formheaderx..","..formheadery..";" ..F(S("Crafting")).."]",
 			"listcolors[#00000000;#00000000]",
-			"list[current_player;craftpreview;"..(craftresultx+0.15)..","..(crafty+0.15)..";1,1;]",
-			"list[current_player;craft;"..(craftx+0.15)..","..(crafty+0.15)..";3,3;]",
 			"listring[current_name;craft]",
 			"listring[current_player;main]"
 		}
@@ -187,18 +185,15 @@ ui.register_page("craft", {
 
 		if ui.trash_enabled or ui.is_creative(player_name) or minetest.get_player_privs(player_name).give then
 			formspec[n] = string.format("label[%f,%f;%s]", craftx + 6.45, crafty + 2.4, F(S("Trash:")))
-			formspec[n+1] = string.format("image[%f,%f;%s]", craftx+6.25, crafty + 2.5, ui.trash_slot_img)
-			formspec[n+2] = string.format("list[detached:trash;main;%f,%f;1,1;]", craftx + 6.4, crafty + 2.65)
-			n=n+3
+			formspec[n+1] = ui.make_trash_slot(craftx + 6.25, crafty + 2.5)
+			n=n + 2
 		end
 
 		if ui.is_creative(player_name) then
-			formspec[n] =   string.format("image[%f,%f;%f,%f;ui_single_slot.png]",
-				perplayer_formspec.craft_x - 2.5, perplayer_formspec.craft_y + 2.5,
-				ui.imgscale, ui.imgscale)
+			formspec[n] = ui.single_slot(craftx - 2.5, crafty + 2.5)
 			formspec[n+1] = string.format("label[%f,%f;%s]", craftx - 2.3, crafty + 2.4,F(S("Refill:")))
 			formspec[n+2] = string.format("list[detached:%srefill;main;%f,%f;1,1;]",
-				F(player_name), craftx - 2.35, crafty + 2.65)
+				F(player_name), craftx - 2.2 - ui.list_img_offset, crafty + 2.5 + ui.list_img_offset)
 		end
 		return {formspec=table.concat(formspec)}
 	end,
@@ -275,8 +270,8 @@ ui.register_page("craftguide", {
 
 		local craftx =       perplayer_formspec.craft_x
 		local crafty =       perplayer_formspec.craft_y
-		local craftarrowx =  craftx + 3.75
-		local craftresultx = craftx + 5
+		local craftarrowx =  perplayer_formspec.craftarrow_x
+		local craftresultx = perplayer_formspec.craftresult_x
 		local formheaderx =  perplayer_formspec.form_header_x
 		local formheadery =  perplayer_formspec.form_header_y
 		local give_x =       perplayer_formspec.give_btn_x
@@ -317,7 +312,7 @@ ui.register_page("craftguide", {
 		end
 		local has_give = player_privs.give or ui.is_creative(player_name)
 
-		formspec[n] = "image["..craftarrowx..","..crafty..";1.25,1.25;ui_crafting_arrow.png]"
+		formspec[n] = perplayer_formspec.craftarrow
 		formspec[n+1] = string.format("textarea[%f,%f;10,1;;%s: %s;]",
 				craftx-2.3, perplayer_formspec.resultstr_y, F(role_text[dir]), item_name_shown)
 		n = n + 2