Rewrite falling entity to make use of collision info

fixes #4781, fixes #9293

builtin/game/falling.lua

@@ -30,6 +30,8 @@ local facedir_to_euler = {
 	{y = math.pi/2, x = math.pi, z = 0}
 }
 
+local gravity = tonumber(core.settings:get("movement_gravity")) or 9.81
+
 --
 -- Falling stuff
 --
@@ -47,6 +49,7 @@ core.register_entity(":__builtin:falling_node", {
 
 	node = {},
 	meta = {},
+	floats = false,
 
 	set_node = function(self, node, meta)
 		self.node = node
@@ -71,6 +74,11 @@ core.register_entity(":__builtin:falling_node", {
 			return
 		end
 		self.meta = meta
+
+		-- Cache whether we're supposed to float on water
+		self.floats = core.get_item_group(node.name, "float") ~= 0
+
+		-- Set entity visuals
 		if def.drawtype == "torchlike" or def.drawtype == "signlike" then
 			local textures
 			if def.tiles and def.tiles[1] then
@@ -113,6 +121,7 @@ core.register_entity(":__builtin:falling_node", {
 				glow = def.light_source,
 			})
 		end
+
 		-- Rotate entity
 		if def.drawtype == "torchlike" then
 			self.object:set_yaw(math.pi*0.25)
@@ -172,6 +181,7 @@ core.register_entity(":__builtin:falling_node", {
 
 	on_activate = function(self, staticdata)
 		self.object:set_armor_groups({immortal = 1})
+		self.object:set_acceleration({x = 0, y = -gravity, z = 0})
 
 		local ds = core.deserialize(staticdata)
 		if ds and ds.node then
@@ -183,28 +193,9 @@ core.register_entity(":__builtin:falling_node", {
 		end
 	end,
 
-	on_step = function(self, dtime)
+	try_place = function(self, bcp, bcn)
-		-- Set gravity
+		local bcd = core.registered_nodes[bcn.name]
-		local acceleration = self.object:get_acceleration()
+		-- Add levels if dropped on same leveled node
-		if not vector.equals(acceleration, {x = 0, y = -10, z = 0}) then
-			self.object:set_acceleration({x = 0, y = -10, z = 0})
-		end
-		-- Turn to actual node when colliding with ground, or continue to move
-		local pos = self.object:get_pos()
-		-- Position of bottom center point
-		local bcp = {x = pos.x, y = pos.y - 0.7, z = pos.z}
-		-- 'bcn' is nil for unloaded nodes
-		local bcn = core.get_node_or_nil(bcp)
-		-- Delete on contact with ignore at world edges
-		if bcn and bcn.name == "ignore" then
-			self.object:remove()
-			return
-		end
-		local bcd = bcn and core.registered_nodes[bcn.name]
-		if bcn and
-				(not bcd or bcd.walkable or
-				(core.get_item_group(self.node.name, "float") ~= 0 and
-				bcd.liquidtype ~= "none")) then
 		if bcd and bcd.leveled and
 				bcn.name == self.node.name then
 			local addlevel = self.node.level
@@ -212,57 +203,128 @@ core.register_entity(":__builtin:falling_node", {
 				addlevel = bcd.leveled
 			end
 			if core.add_node_level(bcp, addlevel) == 0 then
-					self.object:remove()
+				return true
-					return
 			end
-			elseif bcd and bcd.buildable_to and
+		end
-					(core.get_item_group(self.node.name, "float") == 0 or
+
-					bcd.liquidtype == "none") then
+		-- Decide if we're replacing the node or placing on top
+		local np = vector.new(bcp)
+		if bcd and bcd.buildable_to and
+				(not self.floats or bcd.liquidtype == "none") then
 			core.remove_node(bcp)
-				return
+		else
+			np.y = np.y + 1
 		end
-			local np = {x = bcp.x, y = bcp.y + 1, z = bcp.z}
+
 		-- Check what's here
 		local n2 = core.get_node(np)
 		local nd = core.registered_nodes[n2.name]
 		-- If it's not air or liquid, remove node and replace it with
 		-- it's drops
 		if n2.name ~= "air" and (not nd or nd.liquidtype == "none") then
-				core.remove_node(np)
 			if nd and nd.buildable_to == false then
-					-- Add dropped items
+				nd.on_dig(np, n2, nil)
-					local drops = core.get_node_drops(n2, "")
+				-- If it's still there, it might be protected
-					for _, dropped_item in pairs(drops) do
+				if core.get_node(np).name == n2.name then
-						core.add_item(np, dropped_item)
+					return false
+				end
+			else
+				core.remove_node(np)
 			end
 		end
-				-- Run script hook
+
-				for _, callback in pairs(core.registered_on_dignodes) do
+		-- Create node
-					callback(np, n2)
-				end
-			end
-			-- Create node and remove entity
 		local def = core.registered_nodes[self.node.name]
 		if def then
 			core.add_node(np, self.node)
 			if self.meta then
-					local meta = core.get_meta(np)
+				core.get_meta(np):from_table(self.meta)
-					meta:from_table(self.meta)
 			end
 			if def.sounds and def.sounds.place then
 				core.sound_play(def.sounds.place, {pos = np}, true)
 			end
 		end
-			self.object:remove()
 		core.check_for_falling(np)
+		return true
+	end,
+
+	on_step = function(self, dtime, moveresult)
+		-- Fallback code since collision detection can't tell us
+		-- about liquids (which do not collide)
+		if self.floats then
+			local pos = self.object:get_pos()
+
+			local bcp = vector.round({x = pos.x, y = pos.y - 0.7, z = pos.z})
+			local bcn = core.get_node(bcp)
+
+			local bcd = core.registered_nodes[bcn.name]
+			if bcd and bcd.liquidtype ~= "none" then
+				if self:try_place(bcp, bcn) then
+					self.object:remove()
 					return
 				end
-		local vel = self.object:get_velocity()
-		if vector.equals(vel, {x = 0, y = 0, z = 0}) then
-			local npos = self.object:get_pos()
-			self.object:set_pos(vector.round(npos))
 			end
 		end
+
+		assert(moveresult)
+		if not moveresult.collides then
+			return -- Nothing to do :)
+		end
+
+		local bcp, bcn
+		if moveresult.touching_ground then
+			for _, info in ipairs(moveresult.collisions) do
+				if info.axis == "y" then
+					bcp = info.node_pos
+					bcn = core.get_node(bcp)
+					break
+				end
+			end
+		end
+
+		if not bcp then
+			-- We're colliding with something, but not the ground. Irrelevant to us.
+			return
+		elseif bcn.name == "ignore" then
+			-- Delete on contact with ignore at world edges
+			self.object:remove()
+			return
+		end
+
+		local failure = false
+
+		local pos = self.object:get_pos()
+		local distance = vector.apply(vector.subtract(pos, bcp), math.abs)
+		if distance.x >= 1 or distance.z >= 1 then
+			-- We're colliding with some part of a node that's sticking out
+			-- Since we don't want to visually teleport, drop as item
+			failure = true
+		elseif distance.y >= 2 then
+			-- Doors consist of a hidden top node and a bottom node that is
+			-- the actual door. Despite the top node being solid, the moveresult
+			-- almost always indicates collision with the bottom node.
+			-- Compensate for this by checking the top node
+			bcp.y = bcp.y + 1
+			bcn = core.get_node(bcp)
+			local def = core.registered_nodes[bcn.name]
+			if not (def and def.walkable) then
+				failure = true -- This is unexpected, fail
+			end
+		end
+
+		-- Try to actually place ourselves
+		if not failure then
+			failure = not self:try_place(bcp, bcn)
+		end
+
+		if failure then
+			local drops = core.get_node_drops(self.node, "")
+			for _, item in pairs(drops) do
+				core.add_item(pos, item)
+			end
+		end
+		self.object:remove()
+	end
 })
 
 local function convert_to_falling_node(pos, node)