Add antialiasing UI setting

The Irrlicht engine supports antialiasing, and Minetest already supports
saving an antialiasing setting in its configuration file.  However,
Minetest lacked UI elements to set this setting, and previously the only
way to enable the feature was by hand-editing the configuration file.

Add a drop-down menu that can enable antialiasing.

builtin/mainmenu/tab_settings.lua

@@ -60,6 +60,19 @@ local function getLeavesStyleSettingIndex()
 	return 1
 end
 
+local dd_antialiasing_labels = {
+	fgettext("None"),
+	fgettext("2x"),
+	fgettext("4x"),
+	fgettext("8x"),
+}
+
+local antialiasing = {
+   {dd_antialiasing_labels[1]..","..dd_antialiasing_labels[2]..","..
+       dd_antialiasing_labels[3]..","..dd_antialiasing_labels[4]},
+   {"0", "2", "4", "8"}
+}
+
 local function getFilterSettingIndex()
 	if (core.setting_get(filters[2][3]) == "true") then
 		return 3
@@ -80,6 +93,26 @@ local function getMipmapSettingIndex()
 	return 1
 end
 
+local function getAntialiasingSettingIndex()
+	local antialiasing_setting = core.setting_get("fsaa")
+	for i=1, #(antialiasing[2]) do
+		if antialiasing_setting == antialiasing[2][i] then
+			return i
+		end
+	end
+	return 1
+end
+
+local function antialiasing_fname_to_name(fname)
+   for i=1, #(dd_antialiasing_labels) do
+      if fname == dd_antialiasing_labels[i] then
+         return antialiasing[2][i]
+      end
+   end
+
+   return "0"
+end
+
 local function video_driver_fname_to_name(selected_driver)
 	local video_drivers = core.get_video_drivers()
 
@@ -214,13 +247,17 @@ local function formspec(tabview, name, tabdata)
 		"dropdown[0.25,3.2;3.3;dd_leaves_style;" .. leaves_style[1][1] .. ";"
 				.. getLeavesStyleSettingIndex() .. "]" ..
 		"box[3.75,0;3.75,3.45;#999999]" ..
+		"box[3.75,0;3.75,4.7;#999999]" ..
 		"label[3.85,0.1;".. fgettext("Texturing:") .. "]"..
 		"dropdown[3.85,0.55;3.85;dd_filters;" .. filters[1][1] .. ";"
 				.. getFilterSettingIndex() .. "]" ..
 		"dropdown[3.85,1.35;3.85;dd_mipmap;" .. mipmap[1][1] .. ";"
 				.. getMipmapSettingIndex() .. "]" ..
-		"label[3.85,2.15;".. fgettext("Rendering:") .. "]"..
-		"dropdown[3.85,2.6;3.85;dd_video_driver;"
+		"label[3.85,2.15;".. fgettext("Antialiasing:") .. "]"..
+		"dropdown[3.85,2.6;3.85;dd_antialiasing;" .. antialiasing[1][1] .. ";"
+		.. getAntialiasingSettingIndex() .. "]" ..
+		"label[3.85,3.4;".. fgettext("Rendering:") .. "]"..
+		"dropdown[3.85,3.85;3.85;dd_video_driver;"
 				.. driver_formspec_string .. ";" .. driver_current_idx .. "]" ..
 		"tooltip[dd_video_driver;" ..
 				fgettext("Restart minetest for driver change to take effect") .. "]" ..
@@ -421,6 +458,8 @@ local function handle_settings_buttons(this, fields, tabname, tabdata)
 		core.setting_set("anisotropic_filter", "true")
 		ddhandled = true
 	end
+	core.setting_set("fsaa",
+		antialiasing_fname_to_name(fields["dd_antialiasing"]))
 
 	return ddhandled
 end