Add effect metadata

Effect metadata is a means to store additional user-defined data for the effect,
which can be reused when the cancel function of the effect is called.
This commit also adds a new example (blind) to demonstrate usage of that.

examples.lua

@@ -1,4 +1,20 @@
 ----- EXAMPLE EFFECT TYPES -----
+-- Makes the player screen black for 5 seconds (very experimental!)
+playereffects.register_effect_type("blind", "Blind", nil, {},
+	function(player)
+		local hudid = player:hud_add({
+			hud_elem_type = "image",
+			position = { x=0.5, y=0.5 },
+			scale = { x=-100, y=-100 },
+			text = "playereffects_example_black.png",
+		})
+		return { hudid = hudid }
+	end,
+	function(effect)
+		local player = minetest.get_player_by_name(effect.playername)
+		player:hud_remove(effect.metadata.hudid)
+	end
+)
 
 -- Makes the user faster
 playereffects.register_effect_type("high_speed", "High speed", nil, {"speed"}, 
@@ -75,7 +91,14 @@ playereffects.register_effect_type("stress", "Stress Test Effect", nil, {},
 
 
 ------ Chat commands for the example effects ------
-
+minetest.register_chatcommand("blind", {
+	params = "",
+	description = "Makes your screen black for a short time.",
+	privs = {},
+	func = function(name, param)
+		playereffects.apply_effect_type("blind", 5, minetest.get_player_by_name(name))
+	end,
+})
 minetest.register_chatcommand("fast", {
 	params = "",
 	description = "Makes you fast for a short time.",

init.lua

@@ -105,6 +105,8 @@ function playereffects.apply_effect_type(effect_type_id, duration, player)
 		hudids = {text_id=nil, icon_id=nil}
 	end
 
+	local metadata = playereffects.effect_types[effect_type_id].apply(player)
+
 	local effect = {
 			playername = playername, 
 			effect_id = effect_id,
@@ -113,11 +115,11 @@ function playereffects.apply_effect_type(effect_type_id, duration, player)
 			time_left = duration,
 			hudids = hudids,
 			hudpos = free_hudpos,
-			}
+			metadata = metadata,
+	}
 
 	playereffects.effects[effect_id] = effect
-		
-	playereffects.effect_types[effect_type_id].apply(player)
+
 	minetest.log("action", "[playereffects] Effect type "..effect_type_id.." applied to player "..playername.."!")
 	minetest.after(duration, function(effect_id) playereffects.cancel_effect(effect_id) end, effect_id)
 end
@@ -202,6 +204,7 @@ function playereffects.save_to_file()
 			time_left = new_duration,
 			start_time = effect.start_time,
 			playername = effect.playername,
+			metadata = effect.metadata
 		}
 		if(inactive_effects[effect.playername] == nil) then
 			inactive_effects[effect.playername] = {}