Add physics modifiers wrapper mod for player physics overrides (#289)

Closes #288

mods/other/sprint/depends.txt

@@ -1,2 +1,3 @@
 medkits
+physics
 hudbars?

mods/other/sprint/init.lua

@@ -7,10 +7,6 @@ local MOD_JUMP    = tonumber(minetest.settings:get("sprint_jump")      or 1.1)
 local STAMINA_MAX = tonumber(minetest.settings:get("sprint_stamina")   or 20)
 local HEAL_RATE   = tonumber(minetest.settings:get("sprint_heal_rate") or 0.5)
 local MIN_SPRINT  = tonumber(minetest.settings:get("sprint_min")       or 0.5)
-local SPRINT_MODIFIERS = {
-	[true]  = { speed = MOD_WALK, jump = MOD_JUMP },
-	[false] = { speed = 1.0,      jump = 1.0      },
-}
 
 if minetest.get_modpath("hudbars") ~= nil then
 	hb.register_hudbar("sprint", 0xFFFFFF, "Stamina",
@@ -27,7 +23,14 @@ local players = {}
 
 local function setSprinting(player, info, sprinting)
 	if info.sprinting ~= sprinting then
-		player:set_physics_override(SPRINT_MODIFIERS[sprinting])
+		if sprinting then
+			physics.set(player:get_player_name(), "sprint:sprint", {
+				speed = MOD_WALK,
+				jump  = MOD_JUMP
+			})
+		else
+			physics.remove(player:get_player_name(), "sprint:sprint")
+		end
 		info.sprinting = sprinting
 	end
 end

mods/physics/init.lua

@@ -0,0 +1,47 @@
+physics = {}
+
+local players = {}
+
+minetest.register_on_joinplayer(function(player)
+	players[player:get_player_name()] = {}
+end)
+
+minetest.register_on_leaveplayer(function(player)
+	players[player:get_player_name()] = nil
+end)
+
+local function update(name)
+	assert(players[name])
+	local player = minetest.get_player_by_name(name)
+	local override = {
+		speed   = 1,
+		jump    = 1,
+		gravity = 1
+	}
+
+	for _, layer in pairs(players[name]) do
+		for attr, val in pairs(layer) do
+			override[attr] = override[attr] * val
+		end
+	end
+
+	player:set_physics_override(override)
+end
+
+function physics.set(pname, name, modifiers)
+	assert(players[pname] and not players[pname][name])
+	players[pname][name] = modifiers
+	update(pname)
+end
+
+function physics.change(pname, name, modifier)
+	assert(players[pname] and players[pname][name])
+	players[pname][name] = modifier
+	update(pname)
+end
+
+function physics.remove(pname, name)
+	assert(players[pname] and players[pname][name])
+	players[pname][name] = nil
+	update(pname)
+end