Rewrite builtin item entity to use collision info

fixes #8967

builtin/game/item_entity.lua

@@ -34,7 +34,6 @@ core.register_entity(":__builtin:item", {
 
 	itemstring = "",
 	moving_state = true,
-	slippery_state = false,
 	physical_state = true,
 	-- Item expiry
 	age = 0,
@@ -157,7 +156,7 @@ core.register_entity(":__builtin:item", {
 		end
 	end,
 
-	on_step = function(self, dtime)
+	on_step = function(self, dtime, moveresult)
 		self.age = self.age + dtime
 		if time_to_live > 0 and self.age > time_to_live then
 			self.itemstring = ""
@@ -178,6 +177,36 @@ core.register_entity(":__builtin:item", {
 			return
 		end
 
+		if self.force_out then
+			-- This code runs after the entity got a push from the is_stuck code.
+			-- It makes sure the entity is entirely outside the solid node
+			local c = self.object:get_properties().collisionbox
+			local s = self.force_out_start
+			local f = self.force_out
+			local ok = (f.x > 0 and pos.x + c[1] > s.x + 0.5) or
+				(f.y > 0 and pos.y + c[2] > s.y + 0.5) or
+				(f.z > 0 and pos.z + c[3] > s.z + 0.5) or
+				(f.x < 0 and pos.x + c[4] < s.x - 0.5) or
+				(f.z < 0 and pos.z + c[6] < s.z - 0.5)
+			if ok then
+				-- Item was successfully forced out
+				self.force_out = nil
+				self:enable_physics()
+				return
+			end
+		end
+
+		if not self.physical_state then
+			return -- Don't do anything
+		end
+
+		assert(moveresult)
+		if not moveresult.collides then
+			-- future TODO: items should probably decelerate in air
+			return
+		end
+
+		-- Push item out when stuck inside solid node
 		local is_stuck = false
 		local snode = core.get_node_or_nil(pos)
 		if snode then
@@ -187,7 +216,6 @@ core.register_entity(":__builtin:item", {
 				and (sdef.node_box == nil or sdef.node_box.type == "regular")
 		end
 
-		-- Push item out when stuck inside solid node
 		if is_stuck then
 			local shootdir
 			local order = {
@@ -223,69 +251,49 @@ core.register_entity(":__builtin:item", {
 				self.force_out_start = vector.round(pos)
 				return
 			end
-		elseif self.force_out then
-			-- This code runs after the entity got a push from the above code.
-			-- It makes sure the entity is entirely outside the solid node
-			local c = self.object:get_properties().collisionbox
-			local s = self.force_out_start
-			local f = self.force_out
-			local ok = (f.x > 0 and pos.x + c[1] > s.x + 0.5) or
-				(f.y > 0 and pos.y + c[2] > s.y + 0.5) or
-				(f.z > 0 and pos.z + c[3] > s.z + 0.5) or
-				(f.x < 0 and pos.x + c[4] < s.x - 0.5) or
-				(f.z < 0 and pos.z + c[6] < s.z - 0.5)
-			if ok then
-				-- Item was successfully forced out
-				self.force_out = nil
-				self:enable_physics()
-			end
 		end
 
-		if not self.physical_state then
-			return -- Don't do anything
+		node = nil -- ground node we're colliding with
+		if moveresult.touching_ground then
+			for _, info in ipairs(moveresult.collisions) do
+				if info.axis == "y" then
+					node = core.get_node(info.node_pos)
+					break
+				end
+			end
 		end
 
 		-- Slide on slippery nodes
-		local vel = self.object:get_velocity()
 		local def = node and core.registered_nodes[node.name]
-		local is_moving = (def and not def.walkable) or
-			vel.x ~= 0 or vel.y ~= 0 or vel.z ~= 0
-		local is_slippery = false
+		local keep_movement = false
 
-		if def and def.walkable then
+		if def then
 			local slippery = core.get_item_group(node.name, "slippery")
-			is_slippery = slippery ~= 0
-			if is_slippery and (math.abs(vel.x) > 0.2 or math.abs(vel.z) > 0.2) then
+			local vel = self.object:get_velocity()
+			if slippery ~= 0 and (math.abs(vel.x) > 0.1 or math.abs(vel.z) > 0.1) then
 				-- Horizontal deceleration
-				local slip_factor = 4.0 / (slippery + 4)
-				self.object:set_acceleration({
-					x = -vel.x * slip_factor,
+				local factor = math.min(4 / (slippery + 4) * dtime, 1)
+				self.object:set_velocity({
+					x = vel.x * (1 - factor),
 					y = 0,
-					z = -vel.z * slip_factor
+					z = vel.z * (1 - factor)
 				})
-			elseif vel.y == 0 then
-				is_moving = false
+				keep_movement = true
 			end
 		end
 
-		if self.moving_state == is_moving and
-				self.slippery_state == is_slippery then
+		if not keep_movement then
+			self.object:set_velocity({x=0, y=0, z=0})
+		end
+
+		if self.moving_state == keep_movement then
 			-- Do not update anything until the moving state changes
 			return
 		end
+		self.moving_state = keep_movement
 
-		self.moving_state = is_moving
-		self.slippery_state = is_slippery
-
-		if is_moving then
-			self.object:set_acceleration({x = 0, y = -gravity, z = 0})
-		else
-			self.object:set_acceleration({x = 0, y = 0, z = 0})
-			self.object:set_velocity({x = 0, y = 0, z = 0})
-		end
-
-		--Only collect items if not moving
-		if is_moving then
+		-- Only collect items if not moving
+		if self.moving_state then
 			return
 		end
 		-- Collect the items around to merge with