scripts/modules/mesh_gen.gd

extends Node
##
## MeshGenModule - procedural primitive generators (Features 1-20).
##
## Every generator returns a MeshData Dictionary so it can be built for a
## MeshPool mesh via VertexBufferManager. Nothing here allocates GPU buffers
## until commit() is called, keeping generation cheap and evictable.
##
## MeshData := { verts: PackedVector3Array, indices: PackedInt32Array, uvs }
##

var _host: Node = null
var _root: Node3D = null


func _activate(host: Node) -> void:
	_host = host
	_root = host.get_node_or_null("Geometry") as Node3D
	print("[MeshGen] activated")

func _deactivate() -> void:
	_host = null
	_root = null


func _make_mesh_data() -> Dictionary:
	return {
		"verts": PackedVector3Array(),
		"indices": PackedInt32Array(),
		"uvs": PackedVector2Array(),
	}


## --- Public generator API ---------------------------------------------------

func generate(kind: String, params: Dictionary = {}) -> Dictionary:
	match kind:
		"cube":     return cube(float(params.get("size", 1.0)))
		"sphere":   return uv_sphere(int(params.get("rings", 16)), int(params.get("segments", 24)), float(params.get("radius", 0.5)))
		"cylinder": return cylinder(int(params.get("segments", 24)), float(params.get("top_r", 0.5)), float(params.get("bottom_r", 0.5)), float(params.get("height", 1.0)))
		"plane":    return plane(int(params.get("subdiv", 1)), float(params.get("size", 2.0)))
		"torus":    return torus(int(params.get("major_seg", 24)), int(params.get("minor_seg", 12)), float(params.get("major_r", 0.6)), float(params.get("minor_r", 0.2)))
		"ico":      return icosphere(int(params.get("subdiv", 1)), float(params.get("radius", 0.5)))
		"suzanne":  return suzanne(float(params.get("scale", 1.0)))
		_:
			push_warning("MeshGen: unknown kind '%s'" % kind)
			return _make_mesh_data()


## --- Generators -------------------------------------------------------------

func cube(size: float) -> Dictionary:
	var d := _make_mesh_data()
	var h := size * 0.5
	var faces := [
		# (normal, tangent, bitangent) for +X,-X,+Y,-Y,+Z,-Z
		[Vector3.RIGHT, Vector3.BACK, Vector3.UP],
		[Vector3.LEFT, Vector3.FORWARD, Vector3.UP],
		[Vector3.UP, Vector3.RIGHT, Vector3.BACK],
		[Vector3.DOWN, Vector3.RIGHT, Vector3.FORWARD],
		[Vector3.BACK, Vector3.RIGHT, Vector3.UP],
		[Vector3.FORWARD, Vector3.LEFT, Vector3.UP],
	]
	for f in faces:
		var n: Vector3 = f[0]
		var t: Vector3 = f[1]
		var b: Vector3 = f[2]
		var base: int = d["verts"].size()
		var c := n * h
		d["verts"].append(c - t * h - b * h)
		d["verts"].append(c + t * h - b * h)
		d["verts"].append(c + t * h + b * h)
		d["verts"].append(c - t * h + b * h)
		d["uvs"].append(Vector2(0, 0))
		d["uvs"].append(Vector2(1, 0))
		d["uvs"].append(Vector2(1, 1))
		d["uvs"].append(Vector2(0, 1))
		d["indices"].append(base + 0); d["indices"].append(base + 1); d["indices"].append(base + 2)
		d["indices"].append(base + 0); d["indices"].append(base + 2); d["indices"].append(base + 3)
	return d


func uv_sphere(rings: int, segments: int, radius: float) -> Dictionary:
	var d := _make_mesh_data()
	rings = maxi(2, rings)
	segments = maxi(3, segments)
	for y in range(rings + 1):
		var v := float(y) / float(rings)
		var phi := v * PI
		for x in range(segments + 1):
			var u := float(x) / float(segments)
			var theta := u * TAU
			var pos := Vector3(
				sin(phi) * cos(theta),
				cos(phi),
				sin(phi) * sin(theta)
			) * radius
			d["verts"].append(pos)
			d["uvs"].append(Vector2(u, v))
	for y in range(rings):
		for x in range(segments):
			var a := y * (segments + 1) + x
			var b := a + segments + 1
			d["indices"].append(a); d["indices"].append(b); d["indices"].append(a + 1)
			d["indices"].append(a + 1); d["indices"].append(b); d["indices"].append(b + 1)
	return d


func cylinder(segments: int, top_r: float, bottom_r: float, height: float) -> Dictionary:
	var d := _make_mesh_data()
	segments = maxi(3, segments)
	var hy := height * 0.5
	for y in range(2):
		var r := top_r if y == 1 else bottom_r
		var yy := hy if y == 1 else -hy
		for x in range(segments + 1):
			var u := float(x) / float(segments)
			var theta := u * TAU
			d["verts"].append(Vector3(cos(theta) * r, yy, sin(theta) * r))
			d["uvs"].append(Vector2(u, float(y)))
	for x in range(segments):
		var a := x
		var b := x + segments + 1
		d["indices"].append(a); d["indices"].append(b); d["indices"].append(a + 1)
		d["indices"].append(a + 1); d["indices"].append(b); d["indices"].append(b + 1)
	# Caps
	var top_center: int = d["verts"].size()
	d["verts"].append(Vector3(0, hy, 0)); d["uvs"].append(Vector2(0.5, 0.5))
	var bot_center: int = d["verts"].size()
	d["verts"].append(Vector3(0, -hy, 0)); d["uvs"].append(Vector2(0.5, 0.5))
	for x in range(segments):
		var theta0 := (float(x) / float(segments)) * TAU
		var theta1 := (float(x + 1) / float(segments)) * TAU
		var t0: int = d["verts"].size()
		d["verts"].append(Vector3(cos(theta0) * top_r, hy, sin(theta0) * top_r)); d["uvs"].append(Vector2(0, 0))
		d["verts"].append(Vector3(cos(theta1) * top_r, hy, sin(theta1) * top_r)); d["uvs"].append(Vector2(1, 0))
		d["indices"].append(top_center); d["indices"].append(t0); d["indices"].append(t0 + 1)
		var b0: int = d["verts"].size()
		d["verts"].append(Vector3(cos(theta0) * bottom_r, -hy, sin(theta0) * bottom_r)); d["uvs"].append(Vector2(0, 0))
		d["verts"].append(Vector3(cos(theta1) * bottom_r, -hy, sin(theta1) * bottom_r)); d["uvs"].append(Vector2(1, 0))
		d["indices"].append(bot_center); d["indices"].append(b0 + 1); d["indices"].append(b0)
	return d


func plane(subdiv: int, size: float) -> Dictionary:
	var d := _make_mesh_data()
	subdiv = maxi(1, subdiv)
	var half := size * 0.5
	for z in range(subdiv + 1):
		for x in range(subdiv + 1):
			var u := float(x) / float(subdiv)
			var v := float(z) / float(subdiv)
			d["verts"].append(Vector3(-half + u * size, 0, -half + v * size))
			d["uvs"].append(Vector2(u, v))
	var row := subdiv + 1
	for z in range(subdiv):
		for x in range(subdiv):
			var a := z * row + x
			var b := a + row
			d["indices"].append(a); d["indices"].append(a + 1); d["indices"].append(b)
			d["indices"].append(a + 1); d["indices"].append(b + 1); d["indices"].append(b)
	return d


func torus(major_seg: int, minor_seg: int, major_r: float, minor_r: float) -> Dictionary:
	var d := _make_mesh_data()
	major_seg = maxi(3, major_seg)
	minor_seg = maxi(3, minor_seg)
	for i in range(major_seg + 1):
		var u := float(i) / float(major_seg) * TAU
		for j in range(minor_seg + 1):
			var v := float(j) / float(minor_seg) * TAU
			var center := Vector3(cos(u) * major_r, 0, sin(u) * major_r)
			var normal := Vector3(cos(u) * cos(v), sin(v), sin(u) * cos(v))
			d["verts"].append(center + normal * minor_r)
			d["uvs"].append(Vector2(float(i) / float(major_seg), float(j) / float(minor_seg)))
	for i in range(major_seg):
		for j in range(minor_seg):
			var a := i * (minor_seg + 1) + j
			var b := a + minor_seg + 1
			d["indices"].append(a); d["indices"].append(b); d["indices"].append(a + 1)
			d["indices"].append(a + 1); d["indices"].append(b); d["indices"].append(b + 1)
	return d


func icosphere(subdiv: int, radius: float) -> Dictionary:
	var d := _make_mesh_data()
	var t := (1.0 + sqrt(5.0)) * 0.5
	var verts := [
		Vector3(-1, t, 0), Vector3(1, t, 0), Vector3(-1, -t, 0), Vector3(1, -t, 0),
		Vector3(0, -1, t), Vector3(0, 1, t), Vector3(0, -1, -t), Vector3(0, 1, -t),
		Vector3(t, 0, -1), Vector3(t, 0, 1), Vector3(-t, 0, -1), Vector3(-t, 0, 1),
	]
	var faces := [
		[0, 11, 5], [0, 5, 1], [0, 1, 7], [0, 7, 10], [0, 10, 11],
		[1, 5, 9], [5, 11, 4], [11, 10, 2], [10, 7, 6], [7, 1, 8],
		[3, 9, 4], [3, 4, 2], [3, 2, 6], [3, 6, 8], [3, 8, 9],
		[4, 9, 5], [2, 4, 11], [6, 2, 10], [8, 6, 7], [9, 8, 1],
	]
	for s in range(maxi(0, subdiv)):
		var new_faces := []
		var cache := {}
		for f in faces:
			var a: int = f[0]; var b: int = f[1]; var c: int = f[2]
			var ab := _midpoint(verts, cache, a, b)
			var bc := _midpoint(verts, cache, b, c)
			var ca := _midpoint(verts, cache, c, a)
			new_faces.append([a, ab, ca])
			new_faces.append([b, bc, ab])
			new_faces.append([c, ca, bc])
			new_faces.append([ab, bc, ca])
		faces = new_faces
	for v in verts:
		d["verts"].append(v.normalized() * radius)
	d["uvs"].resize(d["verts"].size())
	for f in faces:
		d["indices"].append(f[0]); d["indices"].append(f[1]); d["indices"].append(f[2])
	return d


func _midpoint(verts: Array, cache: Dictionary, a: int, b: int) -> int:
	var key := "%d_%d" % [mini(a, b), maxi(a, b)]
	if cache.has(key):
		return cache[key]
	var mid: Vector3 = (verts[a] + verts[b]) * 0.5
	verts.append(mid)
	var idx := verts.size() - 1
	cache[key] = idx
	return idx


## A low-poly "Suzanne"-style monkey head silhouette (ears + cranium + snout).
## Not bit-identical to Blender's Suzanne, but generated purely from code.
func suzanne(scale: float) -> Dictionary:
	var d := _make_mesh_data()
	# Cranium: squashed sphere
	var cranium := uv_sphere(10, 16, 0.6)
	_append(d, cranium["verts"], cranium["indices"], cranium["uvs"], Vector3(0, 0.1, 0) * scale, scale)
	# Snout: a cube-ish extension forward
	var snout := cube(0.4)
	_append(d, snout["verts"], snout["indices"], snout["uvs"], Vector3(0, -0.1, 0.5) * scale, scale)
	# Ears: two flat spheres left/right
	var ear_l := uv_sphere(6, 10, 0.25)
	_append(d, ear_l["verts"], ear_l["indices"], ear_l["uvs"], Vector3(-0.6, 0.35, 0) * scale, scale)
	var ear_r := uv_sphere(6, 10, 0.25)
	_append(d, ear_r["verts"], ear_r["indices"], ear_r["uvs"], Vector3(0.6, 0.35, 0) * scale, scale)
	return d


## Merge a sub-mesh into a target MeshData with an offset and uniform scale.
func _append(dst: Dictionary, verts: PackedVector3Array, indices: PackedInt32Array, uvs: PackedVector2Array, offset: Vector3, s: float) -> void:
	var base: int = dst["verts"].size()
	for v in verts:
		dst["verts"].append(v * s + offset)
	for u in uvs:
		dst["uvs"].append(u)
	for i in indices:
		dst["indices"].append(base + i)


## --- Instantiation helper ---------------------------------------------------

## Build a MeshInstance3D from a generated MeshData and attach under Geometry.
## Returns the instance (caller owns its lifetime; use MeshPool.release on free).
func spawn(kind: String, params: Dictionary = {}) -> MeshInstance3D:
	var data := generate(kind, params)
	return spawn_from_data(data, kind)


func spawn_from_data(data: Dictionary, name_hint: String = "mesh") -> MeshInstance3D:
	var mesh := MeshPool.acquire_mesh()
	VertexBufferManager.commit(data["verts"], data["indices"], data["uvs"], mesh)
	var mi := MeshInstance3D.new()
	mi.name = name_hint.capitalize()
	mi.mesh = mesh
	var mat := StandardMaterial3D.new()
	mat.albedo_color = Color(0.7, 0.72, 0.8)
	mat.shading_mode = BaseMaterial3D.SHADING_MODE_PER_PIXEL
	mi.material_override = mat
	if _root != null:
		_root.add_child(mi)
	return mi