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extends Node3D
## Generic simulator: Blender designs, Godot (Jolt) does the physics.
##
## godot --headless --path godot --fixed-fps 240 -- <config.json>
##
## The .glb exported by Blender is loaded at runtime and every object becomes
## a body according to its name prefix:
## static_* static, exact mesh (ConcavePolygonShape3D)
## box_* static, box the size of the mesh
## gate_* static, box that a "remove" event takes out of the world
## ball_* rigid, sphere
## block_* rigid, box
## Trajectories are recorded in Blender coordinates (Z up), so the render
## script uses them without converting anything.
##
## The prefixes also fix the order bodies are created in: Blender exports
## objects alphabetically, and in a chaotic scene (hundreds of balls on pegs)
## a different creation order gives different trajectories. Keep new prefixes
## in the same alphabetical order (ball_ < box_ < gate_ < static_) or cached
## simulations will no longer match.
var hz := 240 # physics steps per second
var steps_per_frame := 8 # hz / 30 video fps
var cfg: Dictionary
var dynamic_bodies: Array[RigidBody3D] = []
var removable := {} # name -> CollisionObject3D
var tick := 0
var frames: Array = []
var events: Array = []
var scale_f := 1.0 # the world is simulated scale_f times larger
func _ready() -> void:
var args := OS.get_cmdline_user_args()
if args.is_empty():
push_error("missing config.json")
get_tree().quit(1)
return
cfg = JSON.parse_string(FileAccess.get_file_as_string(args[0]))
# Jolt has tolerances in meters (2 cm of allowed penetration): with small
# pieces it is better to simulate at a larger scale. Gravity and positions
# are scaled alike, so the dynamics are the same and the output goes back
# to the original scale.
scale_f = float(cfg.get("scale", 1.0))
# more steps per second = stiffer contacts (tall stacks); the process runs
# with --fixed-fps 240, so each frame does hz/240 steps
hz = int(cfg.get("hz", 240))
# recording fps: 30 for real time, more for slow motion
steps_per_frame = hz / int(cfg.get("fps", 30))
Engine.physics_ticks_per_second = hz
Engine.max_physics_steps_per_frame = maxi(1, hz / 240)
PhysicsServer3D.area_set_param(get_world_3d().space, PhysicsServer3D.AREA_PARAM_GRAVITY,
float(cfg.get("gravity", 9.81)) * scale_f)
events = cfg.get("events", [])
events.sort_custom(func(a, b): return a["t"] < b["t"])
var doc := GLTFDocument.new()
var st := GLTFState.new()
if doc.append_from_file(cfg["glb"], st) != OK:
push_error("could not read " + cfg["glb"])
get_tree().quit(1)
return
var root := doc.generate_scene(st)
add_child(root)
var meshes: Array[MeshInstance3D] = []
_collect(root, meshes)
for mi in meshes:
_create_body(mi)
root.queue_free()
print("[sim] %d dynamic, %d meshes, g=%.2f" % [dynamic_bodies.size(), meshes.size(),
float(cfg.get("gravity", 9.81))])
_record()
func _collect(n: Node, out: Array[MeshInstance3D]) -> void:
if n is MeshInstance3D:
out.append(n)
for c in n.get_children():
_collect(c, out)
func _rule(body_name: String) -> Dictionary:
var r: Dictionary = {}
var longest := -1
for prefix in cfg.get("rules", {}):
if body_name.begins_with(prefix) and prefix.length() > longest:
r = cfg["rules"][prefix]
longest = prefix.length()
return r
func _create_body(mi: MeshInstance3D) -> void:
var body_name := String(mi.name)
var aabb := mi.get_aabb()
aabb = AABB(aabb.position * scale_f, aabb.size * scale_f)
var r := _rule(body_name)
var mat := PhysicsMaterial.new()
mat.friction = float(r.get("friction", 0.5))
mat.bounce = float(r.get("bounce", 0.0))
var body: CollisionObject3D
var shape := CollisionShape3D.new()
if body_name.begins_with("static_"):
body = StaticBody3D.new()
var tri := ConcavePolygonShape3D.new()
var faces := mi.mesh.get_faces()
for n in faces.size():
faces[n] *= scale_f
tri.set_faces(faces)
shape.shape = tri
elif body_name.begins_with("box_") or body_name.begins_with("gate_"):
body = StaticBody3D.new()
var b := BoxShape3D.new()
b.size = aabb.size
shape.shape = b
shape.position = aabb.get_center()
elif body_name.begins_with("ball_") or body_name.begins_with("block_"):
var rb := RigidBody3D.new()
var vol: float
if body_name.begins_with("ball_"):
var s := SphereShape3D.new()
s.radius = aabb.size.x * 0.5
shape.shape = s
vol = 4.0 / 3.0 * PI * pow(s.radius, 3)
else:
var b := BoxShape3D.new()
b.size = aabb.size
shape.shape = b
vol = aabb.size.x * aabb.size.y * aabb.size.z
shape.position = aabb.get_center()
rb.mass = vol * float(r.get("density", 1000.0))
rb.continuous_cd = bool(r.get("ccd", false))
rb.can_sleep = bool(r.get("can_sleep", true))
rb.linear_damp = float(r.get("damping", 0.0))
rb.angular_damp = float(r.get("angular_damping", 0.0))
if r.get("planar", false):
# motion in the board plane (Blender XZ = Godot XY)
rb.axis_lock_linear_z = true
rb.axis_lock_angular_x = true
rb.axis_lock_angular_y = true
for prefix in cfg.get("frozen", []):
if body_name.begins_with(prefix):
rb.freeze = true
rb.freeze_mode = RigidBody3D.FREEZE_MODE_KINEMATIC
body = rb
dynamic_bodies.append(rb)
else:
return
body.name = body_name
if body is StaticBody3D:
body.physics_material_override = mat
else:
(body as RigidBody3D).physics_material_override = mat
body.add_child(shape)
add_child(body)
var tr := mi.global_transform
tr.origin *= scale_f
body.global_transform = tr
removable[body_name] = body
func _physics_process(_delta: float) -> void:
tick += 1
var t := tick / float(hz)
while not events.is_empty() and events[0]["t"] <= t:
_apply(events.pop_front())
if tick % steps_per_frame == 0:
_record()
if t >= float(cfg["duration"]):
_save()
get_tree().quit()
func _apply(ev: Dictionary) -> void:
var prefix: String = ev["prefix"]
var n := 0
for body_name in removable.keys():
if not String(body_name).begins_with(prefix):
continue
var c: CollisionObject3D = removable[body_name]
if not is_instance_valid(c):
continue
n += 1
match ev["action"]:
"remove":
c.queue_free()
"release":
var rb := c as RigidBody3D
rb.freeze = false
rb.sleeping = false
if ev.has("velocity"):
var v: Array = ev["velocity"] # in Blender coordinates
rb.linear_velocity = Vector3(v[0], v[2], -v[1]) * scale_f
if ev.has("spin"):
var w: Array = ev["spin"] # rad/s, Blender axes
rb.angular_velocity = Vector3(w[0], w[2], -w[1])
# a sleeping body never notices its support was removed: wake them all
for rb in dynamic_bodies:
if not rb.freeze:
rb.sleeping = false
print("[sim] t=%.2f %s %s (%d)" % [tick / float(hz), ev["action"], prefix, n])
func _record() -> void:
var row := PackedFloat32Array()
for rb in dynamic_bodies:
var p := rb.global_position / scale_f
var q := rb.global_transform.basis.get_rotation_quaternion()
# Godot (Y up) -> Blender (Z up): (x, y, z) -> (x, -z, y)
row.append_array([p.x, -p.z, p.y, q.w, q.x, -q.z, q.y])
frames.append(row)
func _save() -> void:
# binary: a JSON header in a separate file + raw float32
var out: String = cfg["output"]
var names := []
for rb in dynamic_bodies:
names.append(String(rb.name))
var f := FileAccess.open(out + ".header.json", FileAccess.WRITE)
f.store_string(JSON.stringify({"names": names, "frames": frames.size(),
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