GodotSectors/Scripts/Space/SpaceRegion.gd

@tool
extends SpaceEntity

## Classic 2.5D sector beauty.
##

class_name SpaceRegion

# TODO: Make evelation and height be against the parent.
@export var elevation: float = 0.0
@export var height: float = 100.0
@export var wall_texture: Texture2D
@export var floor_texture: Texture2D
@export var ceiling_texture: Texture2D
@export var top_texture: Texture2D

var _is_convex_cache: bool


func generate_geometry(space: Space) -> Node3D:
	return _generate_geometry(space, true, null)


func _process(delta):
	if Engine.is_editor_hint():
		self.texture = top_texture if top_texture else floor_texture


func _generate_geometry(space: Space,
						looked_from_inside: bool,
						parent_region: SpaceRegion
) -> Node3D:
	var geometry := MeshInstance3D.new()
	geometry.name = name
	geometry.position = Vector3(
		position.x * space.unit_scale,
		0,
		position.y * space.unit_scale,
	)

	var mesh := ArrayMesh.new()
	var surface_count: int = 0

	mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, _generate_wall_arrays(space, looked_from_inside))
	surface_count += 1
	var wall_material := StandardMaterial3D.new()
	wall_material.albedo_texture = wall_texture
	mesh.surface_set_material(surface_count - 1, wall_material)

	if (looked_from_inside):
		mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, _generate_floor_arrays(space))
		surface_count += 1
		var floor_material := StandardMaterial3D.new()
		floor_material.albedo_texture = floor_texture
		mesh.surface_set_material(surface_count - 1, floor_material)

		mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, _generate_ceiling_arrays(space))
		surface_count += 1
		var ceiling_material := StandardMaterial3D.new()
		ceiling_material.albedo_texture = ceiling_texture
		ceiling_material.cull_mode = BaseMaterial3D.CULL_FRONT # todo: Don't require state change
		mesh.surface_set_material(surface_count - 1, ceiling_material)

	if parent_region and not parent_region._is_convex_cache:
		if parent_region.height > height:
			mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, _generate_ceiling_arrays(space))
			surface_count += 1
			var top_material := StandardMaterial3D.new()
			top_material.albedo_texture = top_texture
			mesh.surface_set_material(surface_count - 1, top_material)

	geometry.mesh = mesh

	_is_convex_cache = is_convex()

	for child in get_children():
		if child is SpaceRegion:
			geometry.add_child(child._generate_geometry(space, not looked_from_inside, self))

	geometry.create_trimesh_collision()
	return geometry


func _generate_wall_arrays(space: Space, looked_from_inside: bool) -> Array:
	var polygon = self.polygon
	var polygon_pairs = Array()
	for i in range(-1, polygon.size() - 1):
		polygon_pairs.append([polygon[i], polygon[i+1]])

	var vertices = PackedVector3Array()
	var uvs = PackedVector2Array()
	for line in polygon_pairs:
		_push_line(space, line, vertices, uvs, looked_from_inside)

	var arrays := Array()
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices
	arrays[Mesh.ARRAY_TEX_UV] = uvs

	return arrays


func _push_line(space: Space,
				line: Array,
				vertices: PackedVector3Array,
				uvs: PackedVector2Array,
				looked_from_inside: bool
):
	var v0 := Vector3(
		line[0][0] * space.unit_scale, elevation * space.unit_scale,
		line[0][1] * space.unit_scale)
	var v1 := Vector3(
		line[1][0] * space.unit_scale, (elevation + height) * space.unit_scale,
		line[1][1] * space.unit_scale)
	var v2 := Vector3(
		line[1][0] * space.unit_scale, elevation * space.unit_scale,
		line[1][1] * space.unit_scale)
	var v3 := Vector3(
		line[0][0] * space.unit_scale, (elevation + height) * space.unit_scale,
		line[0][1] * space.unit_scale)

	if looked_from_inside:
		vertices.append_array([v0, v1, v2, v1, v0, v3])
	else:
		vertices.append_array([v0, v2, v1, v1, v3, v0])

	uvs.append(Vector2(0, 1))
	uvs.append(Vector2(1, 0))
	uvs.append(Vector2(1, 1))
	uvs.append(Vector2(1, 0))
	uvs.append(Vector2(0, 1))
	uvs.append(Vector2(0, 0))


func _generate_floor_arrays(space: Space) -> Array:
	var triangulation := Geometry2D.triangulate_polygon(self.polygon)
	var vertices := PackedVector3Array()
	var uvs := PackedVector2Array()
	vertices.resize(triangulation.size())
	uvs.resize(triangulation.size())

	for i in range(triangulation.size()):
		vertices[i] = Vector3(
			self.polygon[triangulation[i]].x * space.unit_scale,
			elevation * space.unit_scale,
			self.polygon[triangulation[i]].y * space.unit_scale,
		)
		uvs[i] = self.polygon[triangulation[i]] * space.unit_scale

	var arrays := Array()
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices
	arrays[Mesh.ARRAY_TEX_UV] = uvs

	return arrays


# todo: Reuse triangulation with the floor
func _generate_ceiling_arrays(space: Space) -> Array:
	var triangulation := Geometry2D.triangulate_polygon(self.polygon)
	var vertices := PackedVector3Array()
	var uvs := PackedVector2Array()
	vertices.resize(triangulation.size())
	uvs.resize(triangulation.size())

	for i in range(triangulation.size()):
		vertices[i] = Vector3(
			self.polygon[triangulation[i]].x * space.unit_scale,
			(elevation + height) * space.unit_scale,
			self.polygon[triangulation[i]].y * space.unit_scale,
		)
		uvs[i] = self.polygon[triangulation[i]] * space.unit_scale

	var arrays := Array()
	arrays.resize(Mesh.ARRAY_MAX)
	arrays[Mesh.ARRAY_VERTEX] = vertices
	arrays[Mesh.ARRAY_TEX_UV] = uvs

	return arrays


## Check whether region polygon forms a convex geometry.
##
## Based on: https://math.stackexchange.com/a/1745427
func is_convex() -> bool:
	if self.polygon.size() < 3:
		return false

	var wSign: float = 0        # First nonzero orientation (positive or negative)

	var xSign: float = 0
	var xFirstSign: float = 0   # Sign of first nonzero edge vector x
	var xFlips: float = 0       # Number of sign changes in x

	var ySign: float = 0
	var yFirstSign: float = 0   # Sign of first nonzero edge vector y
	var yFlips: float = 0       # Number of sign changes in y

	var curr: Vector2 = self.polygon[-2]   # Second-to-last vertex
	var next: Vector2 = self.polygon[-1]   # Last vertex

	for v in self.polygon:      	 	# Each vertex, in order
		var prev: Vector2 = curr        # Previous vertex
		curr = next          			# Current vertex
		next = v             			# Next vertex

		# Previous edge vector ("before"):
		var bx: float = curr.x - prev.x
		var by: float = curr.y - prev.y

		# Next edge vector ("after"):
		var ax: float = next.x - curr.x
		var ay: float = next.y - curr.y

		# Calculate sign flips using the next edge vector ("after"),
		# recording the first sign.
		if ax > 0:
			if xSign == 0:
				xFirstSign = +1
			elif xSign < 0:
				xFlips = xFlips + 1
			xSign = +1
		elif ax < 0:
			if xSign == 0:
				xFirstSign = -1
			elif xSign > 0:
				xFlips = xFlips + 1
			xSign = -1

		if xFlips > 2:
			return false

		if ay > 0:
			if ySign == 0:
				yFirstSign = +1
			elif ySign < 0:
				yFlips = yFlips + 1
			ySign = +1
		elif ay < 0:
			if ySign == 0:
				yFirstSign = -1
			elif ySign > 0:
				yFlips = yFlips + 1
			ySign = -1

		if yFlips > 2:
			return false

		# Find out the orientation of this pair of edges,
		# and ensure it does not differ from previous ones.
		var w := bx * ay - ax * by
		if (wSign == 0) and (w != 0):
			wSign = w
		elif (wSign > 0) and (w < 0):
			return false
		elif (wSign < 0) and (w > 0):
			return false

	# Final/wraparound sign flips:
	if (xSign != 0) and (xFirstSign != 0) and (xSign != xFirstSign):
		xFlips = xFlips + 1
	if (ySign != 0) and (yFirstSign != 0) and (ySign != yFirstSign):
		yFlips = yFlips + 1

	# Concave polygons have two sign flips along each axis.
	if (xFlips != 2) or (yFlips != 2):
		return false

	# This is a convex polygon.
	return true