Get rail reattachment (especially after jumps) working correctly

mods/ENTITIES/mcl_minecarts/functions.lua

@@ -98,6 +98,31 @@ mod.south = south
 mod.east = east
 mod.west = west
 
+--[[
+	mcl_minecarts.snap_direction(dir)
+
+	returns a valid cart direction that has the smallest angle difference to `dir'
+]]
+local VALID_DIRECTIONS = {
+	north, vector.offset(north, 0, 1, 0), vector.offset(north, 0, -1, 0),
+	south, vector.offset(south, 0, 1, 0), vector.offset(south, 0, -1, 0),
+	east,  vector.offset(east,  0, 1, 0), vector.offset(east,  0, -1, 0),
+	west,  vector.offset(west,  0, 1, 0), vector.offset(west,  0, -1, 0),
+}
+function mod.snap_direction(dir)
+	dir = vector.normalize(dir)
+	local best = nil
+	local diff = -1
+	for _,d in pairs(VALID_DIRECTIONS) do
+		local dot = vector.dot(dir,d)
+		if dot > diff then
+			best = d
+			diff = dot
+		end
+	end
+	return best
+end
+
 local CONNECTIONS = { north, south, east, west }
 local HORIZONTAL_STANDARD_RULES = {
 	[N]       = { "", 0, mask = N, score = 1, can_slope = true },

mods/ENTITIES/mcl_minecarts/init.lua

@@ -41,7 +41,6 @@ end
 
 local function detach_minecart(self)
 	local staticdata = self._staticdata
-	print("Detaching minecart")
 
 	staticdata.connected_at = nil
 	self.object:set_velocity(staticdata.dir * staticdata.velocity)
@@ -453,13 +452,15 @@ local function do_detached_movement(self, dtime)
 	local pos_r = vector.round(self.object:get_pos())
 	local node = minetest.get_node(pos_r)
 	if minetest.get_item_group(node.name, "rail") ~= 0 then
-		print("Reconnected railcart at "..tostring(pos_r))
 		staticdata.connected_at = pos_r
 		staticdata.railtype = node.name
 
 		local freebody_velocity = self.object:get_velocity()
-		staticdata.dir = vector.normalize(freebody_velocity)
+		staticdata.dir = mod:get_rail_direction(pos_r, mod.snap_direction(freebody_velocity))
-		staticdata.velocity = vector.length(freebody_velocity)
+
+		-- Use vector projection to only keep the velocity in the new direction of movement on the rail
+		-- https://en.wikipedia.org/wiki/Vector_projection
+		staticdata.velocity = vector.dot(staticdata.dir,freebody_velocity)
 
 		-- Clear freebody movement
 		self.object:set_velocity(vector.new(0,0,0))