Add slippery group for nodes (players/items slide)

builtin/game/item_entity.lua

@@ -99,8 +99,8 @@ core.register_entity(":__builtin:item", {
 			self.itemstring = staticdata
 		end
 		self.object:set_armor_groups({immortal = 1})
-		self.object:setvelocity({x = 0, y = 2, z = 0})
-		self.object:setacceleration({x = 0, y = -10, z = 0})
+		self.object:set_velocity({x = 0, y = 2, z = 0})
+		self.object:set_acceleration({x = 0, y = -10, z = 0})
 		self:set_item(self.itemstring)
 	end,
 
@@ -177,8 +177,8 @@ core.register_entity(":__builtin:item", {
 		local in_unloaded = (node == nil)
 		if in_unloaded then
 			-- Don't infinetly fall into unloaded map
-			self.object:setvelocity({x = 0, y = 0, z = 0})
-			self.object:setacceleration({x = 0, y = 0, z = 0})
+			self.object:set_velocity({x = 0, y = 0, z = 0})
+			self.object:set_acceleration({x = 0, y = 0, z = 0})
 			self.physical_state = false
 			self.object:set_properties({physical = false})
 			return
@@ -186,7 +186,8 @@ core.register_entity(":__builtin:item", {
 		local nn = node.name
 		-- If node is not registered or node is walkably solid and resting on nodebox
 		local v = self.object:getvelocity()
-		if not core.registered_nodes[nn] or core.registered_nodes[nn].walkable and v.y == 0 then
+		if not core.registered_nodes[nn] or (core.registered_nodes[nn].walkable and
+				core.get_item_group(nn, "slippery") == 0) and v.y == 0 then
 			if self.physical_state then
 				local own_stack = ItemStack(self.object:get_luaentity().itemstring)
 				-- Merge with close entities of the same item
@@ -199,17 +200,28 @@ core.register_entity(":__builtin:item", {
 						end
 					end
 				end
-				self.object:setvelocity({x = 0, y = 0, z = 0})
-				self.object:setacceleration({x = 0, y = 0, z = 0})
+				self.object:set_velocity({x = 0, y = 0, z = 0})
+				self.object:set_acceleration({x = 0, y = 0, z = 0})
 				self.physical_state = false
 				self.object:set_properties({physical = false})
 			end
 		else
 			if not self.physical_state then
-				self.object:setvelocity({x = 0, y = 0, z = 0})
-				self.object:setacceleration({x = 0, y = -10, z = 0})
+				self.object:set_velocity({x = 0, y = 0, z = 0})
+				self.object:set_acceleration({x = 0, y = -10, z = 0})
 				self.physical_state = true
 				self.object:set_properties({physical = true})
+			elseif minetest.get_item_group(nn, "slippery") ~= 0 then
+				if math.abs(v.x) < 0.2 and math.abs(v.z) < 0.2 then
+					self.object:set_velocity({x = 0, y = 0, z = 0})
+					self.object:set_acceleration({x = 0, y = 0, z = 0})
+					self.physical_state = false
+					self.object:set_properties({
+						physical = false
+					})
+				else
+					self.object:set_acceleration({x = -v.x, y = -10, z = -v.z})
+				end
 			end
 		end
 	end,

doc/lua_api.txt

@@ -1424,6 +1424,9 @@ Another example: Make red wool from white wool and red dye:
 * `soil`: saplings will grow on nodes in this group
 * `connect_to_raillike`: makes nodes of raillike drawtype with same group value
   connect to each other
+* `slippery`: Players and items will slide on the node.
+  Only use `slippery = 3` for now to ensure forwards compatibility.
+
 
 ### Known damage and digging time defining groups
 * `crumbly`: dirt, sand

src/client.cpp

@@ -403,7 +403,7 @@ void Client::step(float dtime)
 	// Control local player (0ms)
 	LocalPlayer *player = m_env.getLocalPlayer();
 	assert(player);
-	player->applyControl(dtime);
+	player->applyControl(dtime, &m_env);
 
 	// Step environment
 	m_env.step(dtime);

src/localplayer.cpp

@@ -444,7 +444,7 @@ void LocalPlayer::move(f32 dtime, Environment *env, f32 pos_max_d)
 	move(dtime, env, pos_max_d, NULL);
 }
 
-void LocalPlayer::applyControl(float dtime)
+void LocalPlayer::applyControl(float dtime, ClientEnvironment *env)
 {
 	// Clear stuff
 	swimming_vertical = false;
@@ -660,9 +660,16 @@ void LocalPlayer::applyControl(float dtime)
 	else
 		incH = incV = movement_acceleration_default * BS * dtime;
 
+	INodeDefManager *nodemgr = env->getGameDef()->ndef();
+	Map *map = &env->getMap();
+	bool slippery = false;
+	const ContentFeatures &f = nodemgr->get(map->getNodeNoEx(getStandingNodePos()));
+	slippery = itemgroup_get(f.groups, "slippery");
 	// Accelerate to target speed with maximum increment
-	accelerateHorizontal(speedH * physics_override_speed, incH * physics_override_speed);
-	accelerateVertical(speedV * physics_override_speed, incV * physics_override_speed);
+	accelerateHorizontal(speedH * physics_override_speed,
+			incH * physics_override_speed, slippery);
+	accelerateVertical(speedV * physics_override_speed,
+			incV * physics_override_speed);
 }
 
 v3s16 LocalPlayer::getStandingNodePos()
@@ -699,12 +706,20 @@ v3f LocalPlayer::getEyeOffset() const
 }
 
 // Horizontal acceleration (X and Z), Y direction is ignored
-void LocalPlayer::accelerateHorizontal(const v3f &target_speed, const f32 max_increase)
+void LocalPlayer::accelerateHorizontal(const v3f &target_speed,
+	const f32 max_increase, bool slippery)
 {
         if (max_increase == 0)
                 return;
 
-        v3f d_wanted = target_speed - m_speed;
+	v3f d_wanted = target_speed - m_speed;
+	if (slippery) {
+		if (target_speed == v3f(0))
+			d_wanted = -m_speed * 0.05f;
+		else
+			d_wanted = target_speed * 0.1f - m_speed * 0.1f;
+	}
+
         d_wanted.Y = 0;
         f32 dl = d_wanted.getLength();
         if (dl > max_increase)

src/localplayer.h

@@ -29,6 +29,7 @@ class Client;
 class Environment;
 class GenericCAO;
 class ClientActiveObject;
+class ClientEnvironment;
 class IGameDef;
 
 enum LocalPlayerAnimations
@@ -78,7 +79,7 @@ public:
 	void old_move(f32 dtime, Environment *env, f32 pos_max_d,
 			std::vector<CollisionInfo> *collision_info);
 
-	void applyControl(float dtime);
+	void applyControl(float dtime, ClientEnvironment *env);
 
 	v3s16 getStandingNodePos();
 	v3s16 getFootstepNodePos();
@@ -143,7 +144,8 @@ public:
 	void setCollisionbox(const aabb3f &box) { m_collisionbox = box; }
 
 private:
-	void accelerateHorizontal(const v3f &target_speed, const f32 max_increase);
+	void accelerateHorizontal(const v3f &target_speed,
+		const f32 max_increase, bool slippery);
 	void accelerateVertical(const v3f &target_speed, const f32 max_increase);
 	bool updateSneakNode(Map *map, const v3f &position, const v3f &sneak_max);