write something there

mods/minetest_game/carts/cart_entity.lua

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+-- carts/cart_entity.lua
+
+-- support for MT game translation.
+local S = carts.get_translator
+
+local cart_entity = {
+	initial_properties = {
+		physical = false, -- otherwise going uphill breaks
+		collisionbox = {-0.5, -0.5, -0.5, 0.5, 0.5, 0.5},
+		visual = "mesh",
+		mesh = "carts_cart.b3d",
+		visual_size = {x=1, y=1},
+		textures = {"carts_cart.png"},
+	},
+
+	driver = nil,
+	punched = false, -- used to re-send velocity and position
+	velocity = {x=0, y=0, z=0}, -- only used on punch
+	old_dir = {x=1, y=0, z=0}, -- random value to start the cart on punch
+	old_pos = nil,
+	old_switch = 0,
+	railtype = nil,
+	attached_items = {}
+}
+
+function cart_entity:on_rightclick(clicker)
+	if not clicker or not clicker:is_player() then
+		return
+	end
+	local player_name = clicker:get_player_name()
+	if self.driver and player_name == self.driver then
+		carts:manage_attachment(clicker, nil)
+	elseif not self.driver then
+		carts:manage_attachment(clicker, self.object)
+		self.driver = player_name
+	end
+end
+
+function cart_entity:on_activate(staticdata, dtime_s)
+	self.object:set_armor_groups({immortal=1})
+	if string.sub(staticdata, 1, string.len("return")) ~= "return" then
+		return
+	end
+	local data = minetest.deserialize(staticdata)
+	if type(data) ~= "table" then
+		return
+	end
+	self.railtype = data.railtype
+	self.old_dir = data.old_dir or self.old_dir
+end
+
+function cart_entity:get_staticdata()
+	return minetest.serialize({
+		railtype = self.railtype,
+		old_dir = self.old_dir
+	})
+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
+		-- Clean up eye height
+		carts:manage_attachment(child, nil)
+		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()
+	if not self.railtype or vector.equals(vel, {x=0, y=0, z=0}) then
+		local node = minetest.get_node(pos).name
+		self.railtype = minetest.get_item_group(node, "connect_to_raillike")
+	end
+	-- Punched by non-player
+	if not puncher or not puncher:is_player() then
+		local cart_dir = carts:get_rail_direction(pos, self.old_dir, nil, nil, self.railtype)
+		if vector.equals(cart_dir, {x=0, y=0, z=0}) then
+			return
+		end
+		self.velocity = vector.multiply(cart_dir, 2)
+		self.punched = true
+		return
+	end
+	-- Player digs cart by sneak-punch
+	if puncher:get_player_control().sneak then
+		if self.sound_handle then
+			minetest.sound_stop(self.sound_handle)
+		end
+		-- Detach driver and items
+		if self.driver then
+			if self.old_pos then
+				self.object:set_pos(self.old_pos)
+			end
+			local player = minetest.get_player_by_name(self.driver)
+			carts:manage_attachment(player, nil)
+		end
+		for _, obj_ in ipairs(self.attached_items) do
+			if obj_ then
+				obj_:set_detach()
+			end
+		end
+		-- Pick up cart
+		local inv = puncher:get_inventory()
+		if not minetest.is_creative_enabled(puncher:get_player_name())
+				or not inv:contains_item("main", "carts:cart") then
+			local leftover = inv:add_item("main", "carts:cart")
+			-- If no room in inventory add a replacement cart to the world
+			if not leftover:is_empty() then
+				minetest.add_item(self.object:get_pos(), leftover)
+			end
+		end
+		self.object:remove()
+		return
+	end
+	-- Player punches cart to alter velocity
+	if puncher:get_player_name() == self.driver then
+		if math.abs(vel.x + vel.z) > carts.punch_speed_max then
+			return
+		end
+	end
+
+	local punch_dir = carts:velocity_to_dir(puncher:get_look_dir())
+	punch_dir.y = 0
+	local cart_dir = carts:get_rail_direction(pos, punch_dir, nil, nil, self.railtype)
+	if vector.equals(cart_dir, {x=0, y=0, z=0}) then
+		return
+	end
+
+	local punch_interval = 1
+	-- Faulty tool registrations may cause the interval to be set to 0 !
+	if tool_capabilities and (tool_capabilities.full_punch_interval or 0) > 0 then
+		punch_interval = tool_capabilities.full_punch_interval
+	end
+	time_from_last_punch = math.min(time_from_last_punch or punch_interval, punch_interval)
+	local f = 2 * (time_from_last_punch / punch_interval)
+
+	self.velocity = vector.multiply(cart_dir, f)
+	self.old_dir = cart_dir
+	self.punched = true
+end
+
+local function rail_on_step_event(handler, obj, dtime)
+	if handler then
+		handler(obj, dtime)
+	end
+end
+
+-- sound refresh interval = 1.0sec
+local function rail_sound(self, dtime)
+	if not self.sound_ttl then
+		self.sound_ttl = 1.0
+		return
+	elseif self.sound_ttl > 0 then
+		self.sound_ttl = self.sound_ttl - dtime
+		return
+	end
+	self.sound_ttl = 1.0
+	if self.sound_handle then
+		local handle = self.sound_handle
+		self.sound_handle = nil
+		minetest.after(0.2, minetest.sound_stop, handle)
+	end
+	local vel = self.object:get_velocity()
+	local speed = vector.length(vel)
+	if speed > 0 then
+		self.sound_handle = minetest.sound_play(
+			"carts_cart_moving", {
+			object = self.object,
+			gain = (speed / carts.speed_max) / 2,
+			loop = true,
+		})
+	end
+end
+
+local function get_railparams(pos)
+	local node = minetest.get_node(pos)
+	return carts.railparams[node.name] or {}
+end
+
+local v3_len = vector.length
+local function rail_on_step(self, dtime)
+	local vel = self.object:get_velocity()
+	if self.punched then
+		vel = vector.add(vel, self.velocity)
+		self.object:set_velocity(vel)
+		self.old_dir.y = 0
+	elseif vector.equals(vel, {x=0, y=0, z=0}) then
+		return
+	end
+
+	local pos = self.object:get_pos()
+	local dir = carts:velocity_to_dir(vel)
+	local dir_changed = not vector.equals(dir, self.old_dir)
+	local update = {}
+
+	if self.old_pos and not self.punched and not dir_changed then
+		local flo_pos = vector.round(pos)
+		local flo_old = vector.round(self.old_pos)
+		if vector.equals(flo_pos, flo_old) then
+			-- Do not check one node multiple times
+			return
+		end
+	end
+
+	local ctrl, player
+
+	-- Get player controls
+	if self.driver then
+		player = minetest.get_player_by_name(self.driver)
+		if player then
+			ctrl = player:get_player_control()
+		end
+	end
+
+	local stop_wiggle = false
+	if self.old_pos and not dir_changed then
+		-- Detection for "skipping" nodes (perhaps use average dtime?)
+		-- It's sophisticated enough to take the acceleration in account
+		local acc = self.object:get_acceleration()
+		local distance = dtime * (v3_len(vel) + 0.5 * dtime * v3_len(acc))
+
+		local new_pos, new_dir = carts:pathfinder(
+			pos, self.old_pos, self.old_dir, distance, ctrl,
+			self.old_switch, self.railtype
+		)
+
+		if new_pos then
+			-- No rail found: set to the expected position
+			pos = new_pos
+			update.pos = true
+			dir = new_dir
+		end
+	elseif self.old_pos and self.old_dir.y ~= 1 and not self.punched then
+		-- Stop wiggle
+		stop_wiggle = true
+	end
+
+	local railparams
+
+	-- dir:         New moving direction of the cart
+	-- switch_keys: Currently pressed L(1) or R(2) key,
+	--              used to ignore the key on the next rail node
+	local switch_keys
+	dir, switch_keys = carts:get_rail_direction(
+		pos, dir, ctrl, self.old_switch, self.railtype
+	)
+	dir_changed = not vector.equals(dir, self.old_dir)
+
+	local acc = 0
+	if stop_wiggle or vector.equals(dir, {x=0, y=0, z=0}) then
+		dir = vector.new(self.old_dir)
+		vel = {x = 0, y = 0, z = 0}
+		local pos_r = vector.round(pos)
+		if not carts:is_rail(pos_r, self.railtype)
+				and self.old_pos then
+			pos = self.old_pos
+		elseif not stop_wiggle then
+			-- End of rail: Smooth out.
+			pos = pos_r
+			dir_changed = false
+			dir.y = 0
+		else
+			pos.y = math.floor(pos.y + 0.5)
+		end
+		update.pos = true
+		update.vel = true
+	else
+		-- Direction change detected
+		if dir_changed then
+			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)
+				update.pos = true
+			end
+		end
+		-- Center on the rail
+		if dir.z ~= 0 and math.floor(pos.x + 0.5) ~= pos.x then
+			pos.x = math.floor(pos.x + 0.5)
+			update.pos = true
+		end
+		if dir.x ~= 0 and math.floor(pos.z + 0.5) ~= pos.z then
+			pos.z = math.floor(pos.z + 0.5)
+			update.pos = true
+		end
+
+		-- Slow down or speed up..
+		acc = dir.y * -4.0
+
+		-- Get rail for corrected position
+		railparams = get_railparams(pos)
+
+		-- no need to check for railparams == nil since we always make it exist.
+		local speed_mod = railparams.acceleration
+		if speed_mod and speed_mod ~= 0 then
+			-- Try to make it similar to the original carts mod
+			acc = acc + speed_mod
+		else
+			-- Handbrake or coast
+			if ctrl and ctrl.down then
+				acc = acc - 3
+			else
+				acc = acc - 0.4
+			end
+		end
+	end
+
+	-- Limit cart speed
+	local vel_len = vector.length(vel)
+	if vel_len > carts.speed_max then
+		vel = vector.multiply(vel, carts.speed_max / vel_len)
+		update.vel = true
+	end
+	if vel_len >= carts.speed_max and acc > 0 then
+		acc = 0
+	end
+
+	self.object:set_acceleration(vector.multiply(dir, acc))
+
+	self.old_pos = vector.round(pos)
+	self.old_dir = vector.new(dir)
+	self.old_switch = switch_keys
+
+	if self.punched then
+		-- Collect dropped items
+		for _, obj_ in pairs(minetest.get_objects_inside_radius(pos, 1)) do
+			local ent = obj_:get_luaentity()
+			-- Careful here: physical_state and disable_physics are item-internal APIs
+			if ent and ent.name == "__builtin:item" and ent.physical_state then
+				ent:disable_physics()
+				obj_:set_attach(self.object, "", {x=0, y=0, z=0}, {x=0, y=0, z=0})
+				self.attached_items[#self.attached_items + 1] = obj_
+			end
+		end
+		self.punched = false
+		update.vel = true
+	end
+
+	railparams = railparams or get_railparams(pos)
+
+	if not (update.vel or update.pos) then
+		rail_on_step_event(railparams.on_step, self, dtime)
+		return
+	end
+
+	local yaw = 0
+	if dir.x < 0 then
+		yaw = 0.5
+	elseif dir.x > 0 then
+		yaw = 1.5
+	elseif dir.z < 0 then
+		yaw = 1
+	end
+	self.object:set_yaw(yaw * math.pi)
+
+	local anim = {x=0, y=0}
+	if dir.y == -1 then
+		anim = {x=1, y=1}
+	elseif dir.y == 1 then
+		anim = {x=2, y=2}
+	end
+	self.object:set_animation(anim, 1, 0)
+
+	if update.vel then
+		self.object:set_velocity(vel)
+	end
+	if update.pos then
+		if dir_changed then
+			self.object:set_pos(pos)
+		else
+			self.object:move_to(pos)
+		end
+	end
+
+	-- call event handler
+	rail_on_step_event(railparams.on_step, self, dtime)
+end
+
+function cart_entity:on_step(dtime)
+	rail_on_step(self, dtime)
+	rail_sound(self, dtime)
+end
+
+minetest.register_entity("carts:cart", cart_entity)
+
+minetest.register_craftitem("carts:cart", {
+	description = S("Cart") .. "\n" .. S("(Sneak+Click to pick up)"),
+	inventory_image = minetest.inventorycube("carts_cart_top.png", "carts_cart_front.png", "carts_cart_side.png"),
+	wield_image = "carts_cart_front.png",
+	on_place = function(itemstack, placer, pointed_thing)
+		local under = pointed_thing.under
+		local node = minetest.get_node(under)
+		local udef = minetest.registered_nodes[node.name]
+		if udef and udef.on_rightclick and
+				not (placer and placer:is_player() and
+				placer:get_player_control().sneak) then
+			return udef.on_rightclick(under, node, placer, itemstack,
+				pointed_thing) or itemstack
+		end
+
+		if pointed_thing.type ~= "node" then
+			return
+		end
+		if carts:is_rail(pointed_thing.under) then
+			minetest.add_entity(pointed_thing.under, "carts:cart")
+		elseif carts:is_rail(pointed_thing.above) then
+			minetest.add_entity(pointed_thing.above, "carts:cart")
+		else
+			return
+		end
+
+		minetest.sound_play({name = "default_place_node_metal", gain = 0.5},
+			{pos = pointed_thing.above}, true)
+
+		local player_name = placer and placer:get_player_name() or ""
+		if not minetest.is_creative_enabled(player_name) then
+			itemstack:take_item()
+		end
+		return itemstack
+	end,
+})
+
+minetest.register_craft({
+	output = "carts:cart",
+	recipe = {
+		{"default:steel_ingot", "", "default:steel_ingot"},
+		{"default:steel_ingot", "default:steel_ingot", "default:steel_ingot"},
+	},
+})