Add intermediate button state for sorttube enabler

Image supplied by VanessaE.

common.lua

@@ -129,15 +129,17 @@ function fs_helpers.cycling_button(meta, base, meta_name, values)
 	local val = values[current_value + 1]
 	local text
 	local texture_name = nil
+	local addopts = nil
 	--when we get a table, we know the caller wants an image_button
 	if type(val) == "table" then
 		text = val["text"]
 		texture_name = val["texture"]
+		addopts = val["addopts"]
 	else
 		text = val
 	end
 	local field = "fs_helpers_cycling:"..new_value..":"..meta_name
-	return base..";"..(texture_name and texture_name..";" or "")..field..";"..minetest.formspec_escape(text).."]"
+	return base..";"..(texture_name and texture_name..";" or "")..field..";"..minetest.formspec_escape(text)..(addopts and ";"..addopts or "").."]"
 end
 
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tubes.lua

@@ -253,7 +253,7 @@ if pipeworks.enable_mese_tube then
 		for i = 0, 5 do
 			buttons_formspec = buttons_formspec .. fs_helpers.cycling_button(meta,
 				"image_button[7,"..(i)..";1,1", "l"..(i+1).."s",
-				{{text="",texture="pipeworks_button_off.png"}, {text="",texture="pipeworks_button_on.png"}})
+				{{text="",texture="pipeworks_button_off.png", addopts="false;false;pipeworks_button_interm.png"}, {text="",texture="pipeworks_button_on.png", addopts="false;false;pipeworks_button_interm.png"}})
 		end
 		meta:set_string("formspec",
 			"size[8,11]"..