Odd-shaped houses (Gitea #7): roofs may run through other roofs (an L, a wing at an angle, roofs at different heights), but not inside an identical one, and nothing else goes through them; the guide explains growing a house

scripts/building/build_system.gd

@@ -162,6 +162,23 @@ func recompute() -> Array:
 
 # --- placement --------------------------------------------------------------
 
+## Roof pieces: these may pass through one another.
+const ROOF_KINDS := ["roof", "roof_ridge"]
+
+## A roof piece of `kind` already sitting at `xf` (the same place, facing
+## the same way), so a second one isn't put inside the first.
+func _same_roof_at(kind: String, xf: Transform3D, exclude: Node) -> bool:
+	for p in build_pieces():
+		if p == exclude or p.kind != kind:
+			continue
+		var pxf: Transform3D = p.global_transform
+		var facing: float = pxf.basis.z.normalized().dot(xf.basis.z.normalized())
+		if kind == "roof_ridge":
+			facing = absf(facing)   # (it's the same both ways round)
+		if pxf.origin.distance_to(xf.origin) < 0.15 and facing > 0.99:
+			return true
+	return false
+
 ## Why a building piece can't go at `xf` ("" = it can).
 func check(def: Dictionary, xf: Transform3D, exclude: Node = null) -> String:
 	var kind: String = def.place.kind
@@ -172,6 +189,9 @@ func check(def: Dictionary, xf: Transform3D, exclude: Node = null) -> String:
 	if c.y < terrain.water_level + 0.1:
 		return "Can't build in water"
 	var space := world.get_world_3d().direct_space_state
+	var roofy: bool = kind in ROOF_KINDS
+	if roofy and _same_roof_at(kind, xf, exclude):
+		return "There's already a roof there"
 	for s in info.shapes:
 		var made := BuildPiece.make_shape(s, OVERLAP_MARGIN)
 		var q := PhysicsShapeQueryParameters3D.new()
@@ -182,9 +202,13 @@ func check(def: Dictionary, xf: Transform3D, exclude: Node = null) -> String:
 		if exclude != null:
 			ex.append(exclude.get_rid())
 		q.exclude = ex
-		var hits := space.intersect_shape(q, 1)
-		if not hits.is_empty():
-			last_blocker = hits[0].collider
+		var hits := space.intersect_shape(q, 8)
+		for h in hits:
+			# Roofs can run through other roofs (Gitea #7: an L, a wing at an
+			# angle, roofs at odd heights), but nothing else.
+			if roofy and h.collider != null and String(h.collider.get("kind")) in ROOF_KINDS:
+				continue
+			last_blocker = h.collider
 			return "Something's in the way"
 	var mat := BuildPiece.material_of(def)
 	if support_for(kind, xf, exclude, mat) < MIN_SUPPORT: