Add spiky box variants

movement.lua

@@ -1,6 +1,6 @@
 -- Finds the complete set of blocks that must move together for one grid step.
 -- A block joins the set when it is in another block's destination (ordinary
--- pushing), is behind a directional sticky puller, or touches a skewer block.
+-- pushing), is softly grabbed by sticky/spiky, or touches a rigid skewer.
 local Movement = {}
 
 local adjacentDirections = {
@@ -22,7 +22,14 @@ local function isSkewer(entity)
 	return entity.isSkewer and entity:isSkewer()
 end
 
-function Movement.findMovableGroup(startCells, direction, entityAt, isInBounds)
+local function isSpiky(entity)
+	return entity.isSpiky and entity:isSpiky()
+end
+
+-- Build one rigid component: ordinary pushes are required, and skewers join
+-- along every edge. `alreadyMoving` contains cells that will be vacated during
+-- this same step, so a later pulled component may move into them.
+local function findRigidGroup(startCells, direction, entityAt, isInBounds, alreadyMoving)
 	local entities = {}
 	local pendingCells = {}
 	for _, cell in ipairs(startCells) do
@@ -39,7 +46,8 @@ function Movement.findMovableGroup(startCells, direction, entityAt, isInBounds)
 		end
 
 		local entity = entityAt(cell)
-		if entity and not isPassable(entity) and not entities[entity] then
+		if entity and not isPassable(entity) and not entities[entity] and
+			not (alreadyMoving and alreadyMoving[entity]) then
 			if not entity:canMove() then
 				return false, entities
 		end
@@ -51,9 +59,7 @@ function Movement.findMovableGroup(startCells, direction, entityAt, isInBounds)
 				table.insert(pendingCells, projectedCell)
 			end
 
-			-- Sticky blocks pull only from the trailing face, like the player. A
-			-- lateral move therefore shears the contact. Skewers retain the older
-			-- all-edge behaviour and make everything they touch one rigid group.
+			-- Skewers make every edge contact part of this rigid component.
 			for _, occupiedCell in ipairs(entity:getOccupiedCells()) do
 				for _, adjacentDirection in ipairs(adjacentDirections) do
 					local adjacentCell = {
@@ -62,13 +68,11 @@ function Movement.findMovableGroup(startCells, direction, entityAt, isInBounds)
 					}
 					if isInBounds(adjacentCell) then
 						local adjacentEntity = entityAt(adjacentCell)
-						local trailing = adjacentDirection.x == -direction.x and
-							adjacentDirection.y == -direction.y
 						local attached = adjacentEntity and (
-							isSkewer(entity) or isSkewer(adjacentEntity) or
-							(trailing and (isSticky(entity) or isSticky(adjacentEntity)))
+							isSkewer(entity) or isSkewer(adjacentEntity)
 						)
-						if attached and adjacentEntity ~= entity and adjacentEntity:canMove() then
+						if attached and adjacentEntity ~= entity and adjacentEntity:canMove() and
+							not (alreadyMoving and alreadyMoving[adjacentEntity]) then
 							table.insert(pendingCells, adjacentCell)
 						end
 					end
@@ -80,4 +84,60 @@ function Movement.findMovableGroup(startCells, direction, entityAt, isInBounds)
 	return true, entities
 end
 
+function Movement.findMovableGroup(startCells, direction, entityAt, isInBounds)
+	local possible, entities = findRigidGroup(
+		startCells, direction, entityAt, isInBounds
+	)
+	if not possible then return false, entities end
+
+	local movingQueue = {}
+	for entity in pairs(entities) do table.insert(movingQueue, entity) end
+	local attemptedPulls = {}
+	local nextMover = 1
+
+	while nextMover <= #movingQueue do
+		local entity = movingQueue[nextMover]
+		nextMover = nextMover + 1
+
+		-- Sticky contact is soft only on the trailing face. Spiky contact is soft
+		-- on every face. Either kind simply releases a blocked rigid component,
+		-- without cancelling this entity or another independently pulled branch.
+		for _, occupiedCell in ipairs(entity:getOccupiedCells()) do
+			for _, adjacentDirection in ipairs(adjacentDirections) do
+				local adjacentCell = {
+					x = occupiedCell.x + adjacentDirection.x,
+					y = occupiedCell.y + adjacentDirection.y,
+				}
+				if isInBounds(adjacentCell) then
+					local adjacentEntity = entityAt(adjacentCell)
+					local trailing = adjacentDirection.x == -direction.x and
+						adjacentDirection.y == -direction.y
+					local softContact = adjacentEntity and (
+						isSpiky(entity) or isSpiky(adjacentEntity) or
+						(trailing and (isSticky(entity) or isSticky(adjacentEntity)))
+					)
+					if softContact and adjacentEntity ~= entity and
+						not entities[adjacentEntity] and not attemptedPulls[adjacentEntity] and
+						adjacentEntity:canMove() then
+						attemptedPulls[adjacentEntity] = true
+						local canPull, pulled = findRigidGroup(
+							{adjacentCell}, direction, entityAt, isInBounds, entities
+						)
+						if canPull then
+							for pulledEntity in pairs(pulled) do
+								if not entities[pulledEntity] then
+									entities[pulledEntity] = pulledEntity
+									table.insert(movingQueue, pulledEntity)
+								end
+							end
+						end
+					end
+				end
+			end
+		end
+	end
+
+	return true, entities
+end
+
 return Movement