Use initial_properties, backup old_pos for loading

Clear driver on leave using the detach callback (0.5.x and later)
Fix upright_sprite attachment position
Fallback to the regular node sound when metal does not exist
Set animation to "stand" on attach

cart_entity.lua

@@ -19,12 +19,14 @@ function boost_cart:on_rail_step(entity, pos, distance)
 end
 
 local cart_entity = {
+	initial_properties = {
 		physical = false,
 		collisionbox = {-0.5, -0.5, -0.5, 0.5, 0.5, 0.5},
 		visual = "mesh",
 		mesh = "cart.x",
 		visual_size = {x=1, y=1},
 		textures = {"cart.png"},
+	},
 
 	driver = nil,
 	punched = false, -- used to re-send velocity and position
@@ -34,15 +36,13 @@ local cart_entity = {
 	old_switch = 0,
 	sound_counter = 0,
 	railtype = nil,
-	attached_items = {},
-	automatic_face_movement_dir = -90.0,
-	automatic_face_movement_max_rotation_per_sec = 360 * 4,
+	attached_items = {}
 }
 
 -- Model and textures
 if boost_cart.mtg_compat then
-	cart_entity.mesh = "carts_cart.b3d"
-	cart_entity.textures = {"carts_cart.png"}
+	cart_entity.initial_properties.mesh = "carts_cart.b3d"
+	cart_entity.initial_properties.textures = {"carts_cart.png"}
 end
 
 function cart_entity:on_rightclick(clicker)
@@ -56,6 +56,12 @@ function cart_entity:on_rightclick(clicker)
 	elseif not self.driver then
 		self.driver = player_name
 		boost_cart:manage_attachment(clicker, self.object)
+
+		if default.player_set_animation then
+			-- player_api(/default) does not update the animation
+			-- when the player is attached, reset to default animation
+			default.player_set_animation(clicker, "stand")
+		end
 	end
 end
 
@@ -71,18 +77,29 @@ function cart_entity:on_activate(staticdata, dtime_s)
 		return
 	end
 	self.railtype = data.railtype
-	if data.old_dir then
-		self.old_dir = data.old_dir
+	self.old_dir = data.old_dir or self.old_dir
+	self.old_pos = data.old_pos or self.old_pos
+	-- Correct the position when the cart drives further after the last 'step()'
+	if self.old_pos and boost_cart:is_rail(self.old_pos, self.railtype) then
+		self.object:set_pos(self.old_pos)
 	end
 end
 
 function cart_entity:get_staticdata()
 	return minetest.serialize({
 		railtype = self.railtype,
-		old_dir = self.old_dir
+		old_dir = self.old_dir,
+		old_pos = self.old_pos
 	})
 end
 
+-- 0.5.x and later: When the driver leaves
+function cart_entity:on_detach_child(child)
+	if child and child:get_player_name() == self.driver then
+		self.driver = nil
+	end
+end
+
 function cart_entity:on_punch(puncher, time_from_last_punch, tool_capabilities, direction)
 	local pos = self.object:get_pos()
 	local vel = self.object:get_velocity()
@@ -218,11 +235,12 @@ function cart_entity:on_step(dtime)
 	)
 	local dir_changed = not vector.equals(dir, self.old_dir)
 
-	local new_acc = {x=0, y=0, z=0}
+	local acc = 0
 	if stop_wiggle or vector.equals(dir, {x=0, y=0, z=0}) then
 		vel = {x=0, y=0, z=0}
 		local pos_r = vector.round(pos)
-		if not boost_cart:is_rail(pos_r, self.railtype) then
+		if not boost_cart:is_rail(pos_r, self.railtype)
+				and self.old_pos then
 			pos = self.old_pos
 		elseif not stop_wiggle then
 			pos = pos_r
@@ -234,7 +252,7 @@ function cart_entity:on_step(dtime)
 	else
 		-- Direction change detected
 		if dir_changed then
-			vel = vector.multiply(dir, v3_len(vel))
+			vel = vector.multiply(dir, math.abs(vel.x + vel.z))
 			update.vel = true
 			if dir.y ~= self.old_dir.y then
 				pos = vector.round(pos)
@@ -252,7 +270,7 @@ function cart_entity:on_step(dtime)
 		end
 
 		-- Calculate current cart acceleration
-		local acc = nil
+		acc = nil
 
 		local acc_meta = minetest.get_meta(pos):get_string("cart_acceleration")
 		if acc_meta == "halt" and not self.punched then
@@ -294,21 +312,20 @@ function cart_entity:on_step(dtime)
 		else
 			acc = 0
 		end
-
-		new_acc = vector.multiply(dir, acc)
 	end
 
-	-- Limits
-	local max_vel = boost_cart.speed_max
-	for _,v in pairs({"x","y","z"}) do
-		if math.abs(vel[v]) > max_vel then
-			vel[v] = boost_cart:get_sign(vel[v]) * max_vel
-			new_acc[v] = 0
+	-- Limit cart speed
+	local vel_len = vector.length(vel)
+	if vel_len > boost_cart.speed_max then
+		vel = vector.multiply(vel, boost_cart.speed_max / vel_len)
 		update.vel = true
 	end
+	if vel_len >= boost_cart.speed_max and acc > 0 then
+		acc = 0
 	end
 
-	self.object:set_acceleration(new_acc)
+	self.object:set_acceleration(vector.multiply(dir, acc))
+
 	self.old_pos = vector.round(pos)
 	local old_y_dir = self.old_dir.y
 	if not vector.equals(dir, {x=0, y=0, z=0}) and not stop_wiggle then
@@ -343,7 +360,6 @@ function cart_entity:on_step(dtime)
 	-- Re-use "dir", localize self.old_dir
 	dir = self.old_dir
 
-	if stop_wiggle then
 	local yaw = 0
 	if dir.x < 0 then
 		yaw = 0.5
@@ -353,7 +369,6 @@ function cart_entity:on_step(dtime)
 		yaw = 1
 	end
 	self.object:set_yaw(yaw * math.pi)
-	end
 
 	local anim = {x=0, y=0}
 	if dir.y == -1 then

doc/mod_api.txt

@@ -0,0 +1,71 @@
+boost_cart API
+==============
+
+This file provides information about the API of boost_cart for the use in
+mods. The API might change slightly when the development goes on, so avoid
+using internal tables or functions which are not documented here.
+
+
+Types
+-----
+
+* `SwitchIgnore` -> `number/nil`
+	* Specifies which player control was pressed. This value is used to prefer
+	  straight rails instead of preferring left and right rail checks.
+		* `1`: Ignore left rail
+		* `2`: Ignore right rail
+		* `nil`: Ignore no rail
+
+
+Entity movement
+---------------
+These functions are grouped so that they make sense and then sorted alphabetically.
+
+* `boost_cart:manage_attachment(player, obj)`
+	* Attaches or detaches the player to/from an object, depending on what is
+	  supplied to `obj`.
+	* `player`: `ObjectRef` of the player
+	* `obj`: `ObjectRef` (to attach) or `nil` (to detach)
+* `boost_cart:get_sign(n)` -> `number`
+	* Returns the sign for the given number. Values: `-1`, `0`, `1`
+	* `n`: any `number`
+* `boost_cart:velocity_to_dir(vel)` -> `vector`
+	* Returns the cart direction depending on `vel`. Each coordinate can have
+	  one of the `get_sign()` return values.
+	* `vel`: velocity as `vector`
+* `boost_cart:boost_rail(pos, amount)`
+	* Sets the rail acceleration for the given position to `amount` and punches
+	  carts which are at the given position.
+	* `pos`: `vector`, rail position
+	* `amount`: `number`, negative to brake, positive to boost
+* `boost_cart:get_rail_direction(pos, dir, ctrl, old_switch, railtype)`
+	-> `vector, SwitchIgnore`
+	* Returns the direction to where the next rail is, and which player control that
+	  should be ignored in the next call.
+	* `pos`: `vector`, position of the cart
+	* `dir`: `vector`, movement direction of the cart (see `velocity_to_dir()`)
+	* `ctrl`: Player controls table or `nil` (no player)
+	* `old_switch`: `SwitchIgnore`
+	* `railtype`: (optional) `number`, gets passed indirectly to `is_rail()`
+
+
+Rail helper functions
+---------------------
+* `boost_cart:get_rail_groups(groups)` -> `table`
+	* Returns a group table with preset values for a common rail node
+	* `groups`: (optional) `table`, additional groups append (or overwrite)
+	* Hint: To register an incompatible rail type, set the group
+	  `connect_to_raillike` to the value returned by
+	  `minetest.raillike_group(new_rail_type)`
+* `boost_cart:is_rail(pos, [railtype])` -> `boolean`
+	* Returns whether the node at `pos` is a rail. When `railtype` is specified,
+	  `true` is only returned when the node is in the same rail group.
+	* `pos`: `vector` of the node to check
+	* `railtype`: (optional) `number`, rail group number
+* `boost_cart:register_rail(name, def)`
+	* Registers a new rail with preset node definition defaults as fallback
+	* `name`: `string`, node name of the new rail
+	* `def`: Node definition table, containing at least the following keys:
+		* `description`
+		* `groups`
+		* `tiles`

functions.lua

@@ -19,6 +19,9 @@ function boost_cart:manage_attachment(player, obj)
 
 	if status then
 		local y_pos = self.old_player_model and 6 or -4
+		if player:get_properties().visual == "upright_sprite" then
+			y_pos = -4
+		end
 		player:set_attach(obj, "", {x=0, y=y_pos, z=0}, {x=0, y=0, z=0})
 		player:set_eye_offset({x=0, y=-4, z=0},{x=0, y=-4, z=0})
 	else
@@ -104,6 +107,16 @@ function boost_cart:get_rail_direction(pos_, dir, ctrl, old_switch, railtype)
 		right.z = -dir.x
 	end
 
+	local straight_priority = ctrl and dir.y ~= 0
+
+	-- Normal, to disallow rail switching up- & downhill
+	if straight_priority then
+		cur = self:check_front_up_down(pos, dir, true, railtype)
+		if cur then
+			return cur
+		end
+	end
+
 	if ctrl then
 		if old_switch == 1 then
 			left_check = false
@@ -127,10 +140,12 @@ function boost_cart:get_rail_direction(pos_, dir, ctrl, old_switch, railtype)
 	end
 
 	-- Normal
+	if not straight_priority then
 		cur = self:check_front_up_down(pos, dir, true, railtype)
 		if cur then
 			return cur
 		end
+	end
 
 	-- Left, if not already checked
 	if left_check then
@@ -208,6 +223,9 @@ function boost_cart:boost_rail(pos, amount)
 end
 
 function boost_cart:register_rail(name, def_overwrite)
+	local sound_func = default.node_sound_metal_defaults
+		or default.node_sound_defaults
+
 	local def = {
 		drawtype = "raillike",
 		paramtype = "light",
@@ -217,7 +235,8 @@ function boost_cart:register_rail(name, def_overwrite)
 		selection_box = {
 			type = "fixed",
 			fixed = {-1/2, -1/2, -1/2, 1/2, -1/2+1/16, 1/2},
-		}
+		},
+		sounds = sound_func()
 	}
 	for k, v in pairs(def_overwrite) do
 		def[k] = v

init.lua

@@ -25,8 +25,8 @@ if not default.player_attached then
 	default.player_attached = {}
 end
 
-minetest.after(1, function()
-	boost_cart.old_player_model = type(player_api) ~= "table"
+minetest.after(0, function()
+	boost_cart.old_player_model = not minetest.global_exists("player_api")
 end)
 
 dofile(boost_cart.modpath.."/functions.lua")

rails.lua

@@ -18,6 +18,15 @@ boost_cart:register_rail(":"..regular_rail_itemname, {
 -- Moreores' copper rail
 if minetest.get_modpath("moreores") then
 	minetest.register_alias("carts:copperrail", "moreores:copper_rail")
+
+	if minetest.raillike_group then
+		-- Ensure that this rail uses the same connect_to_raillike
+		local new_groups = minetest.registered_nodes["moreores:copper_rail"].groups
+		new_groups.connect_to_raillike = minetest.raillike_group("rail")
+		minetest.override_item("moreores:copper_rail", {
+			groups = new_groups
+		})
+	end
 else
 	boost_cart:register_rail(":carts:copperrail", {
 		description = "Copper rail",