fix: GN update for custom geonodes

We also implement `BLField` support for Blender `IDStruct` types.

There's a crash haunting us specifically with the cylinder array. Other
primitives (esp. ring) work just fine, as does previews of nested-linked
node groups. The crash triggers specifically when the file is saved and
reloaded, whereafter all the `load_post` handlers run fine (like -
extremely fine, we can perfectly access and dereference all of the node
groups, seemingly all the objects, etc.). Then, crash.

We're also discovering that `id_properties_ui` is completely useless for
after-the-fact updating of custom properties within sockets. Which is a
great surprise, and I have trouble thinking it's on purpose - the data
is stored somewhere, after all. All the forced updates/redraws/etc. in
the world don't seem to change this.

We may have to go back to the drawing board with dynamically-updated
min/max. The entire infrastructure with `SocketDef` altering sockets
after creation is entirely, _violently_ unsuited to do a static
modification. But the bare fact is, the dynamic modification methods are
falling short. It's kind of important stuff, this stuff.

src/blender_maxwell/__init__.py

@@ -149,6 +149,7 @@ def manage_pydeps(*_):
 	# path_addon_pydeps='',
 	# path_addon_reqs='',
 	# )
+	log.debug('PyDeps: Analyzing Post-File Load')
 	ct.addon.prefs().on_addon_pydeps_changed(show_popup_if_deps_invalid=True)
 
 

src/blender_maxwell/assets/geonodes.py

@@ -220,7 +220,6 @@ class GeoNodes(enum.StrEnum):
 ####################
 def import_geonodes(
 	_geonodes: GeoNodes,
-	force_append: bool = False,
 ) -> bpy.types.GeometryNodeGroup:
 	"""Given vendored GeoNodes tree link/append and return the local datablock.
 
@@ -496,6 +495,7 @@ class GeoNodesToStructureNode(bpy.types.Operator):
 				)
 				bpy.ops.node.select_all(action='DESELECT')
 				node = node_tree.nodes.new(geonodes.dedicated_node_type)
+				node.sim_node_name = asset.name
 				node.select = True
 				node.location.x = node_location[0]
 				node.location.y = node_location[1]
@@ -505,9 +505,9 @@ class GeoNodesToStructureNode(bpy.types.Operator):
 				## Since the node doesn't itself handle the structure, we must.
 				## We just import the GN tree, then attach the data block to the node.
 				if geonodes.dedicated_node_type == 'GeoNodesStructureNodeType':
+					## TODO: Is this too presumptuous? Or a fine little hack?
 					geonodes_data = import_geonodes(asset.name)
 					node.inputs['GeoNodes'].value = geonodes_data
-					## TODO: Is this too presumptuous? Or a fine little hack?
 
 			# Restore the Pre-Modal Mouse Cursor Shape
 			context.window.cursor_modal_restore()

src/blender_maxwell/contracts/bl.py

@@ -53,44 +53,44 @@ BLClass: typ.TypeAlias = (
 	| bpy.types.FileHandler
 )
 BLIDStruct: typ.TypeAlias = (
-	bpy.types.Action,
+	bpy.types.Action
-	bpy.types.Armature,
+	| bpy.types.Armature
-	bpy.types.Brush,
+	| bpy.types.Brush
-	bpy.types.CacheFile,
+	| bpy.types.CacheFile
-	bpy.types.Camera,
+	| bpy.types.Camera
-	bpy.types.Collection,
+	| bpy.types.Collection
-	bpy.types.Curve,
+	| bpy.types.Curve
-	bpy.types.Curves,
+	| bpy.types.Curves
-	bpy.types.FreestyleLineStyle,
+	| bpy.types.FreestyleLineStyle
-	bpy.types.GreasePencil,
+	| bpy.types.GreasePencil
-	bpy.types.Image,
+	| bpy.types.Image
-	bpy.types.Key,
+	| bpy.types.Key
-	bpy.types.Lattice,
+	| bpy.types.Lattice
-	bpy.types.Library,
+	| bpy.types.Library
-	bpy.types.Light,
+	| bpy.types.Light
-	bpy.types.LightProbe,
+	| bpy.types.LightProbe
-	bpy.types.Mask,
+	| bpy.types.Mask
-	bpy.types.Material,
+	| bpy.types.Material
-	bpy.types.Mesh,
+	| bpy.types.Mesh
-	bpy.types.MetaBall,
+	| bpy.types.MetaBall
-	bpy.types.MovieClip,
+	| bpy.types.MovieClip
-	bpy.types.NodeTree,
+	| bpy.types.NodeTree
-	bpy.types.Object,
+	| bpy.types.Object
-	bpy.types.PaintCurve,
+	| bpy.types.PaintCurve
-	bpy.types.Palette,
+	| bpy.types.Palette
-	bpy.types.ParticleSettings,
+	| bpy.types.ParticleSettings
-	bpy.types.PointCloud,
+	| bpy.types.PointCloud
-	bpy.types.Scene,
+	| bpy.types.Scene
-	bpy.types.Screen,
+	| bpy.types.Screen
-	bpy.types.Sound,
+	| bpy.types.Sound
-	bpy.types.Speaker,
+	| bpy.types.Speaker
-	bpy.types.Text,
+	| bpy.types.Text
-	bpy.types.Texture,
+	| bpy.types.Texture
-	bpy.types.VectorFont,
+	| bpy.types.VectorFont
-	bpy.types.Volume,
+	| bpy.types.Volume
-	bpy.types.WindowManager,
+	| bpy.types.WindowManager
-	bpy.types.WorkSpace,
+	| bpy.types.WorkSpace
-	bpy.types.World,
+	| bpy.types.World
 )
 BLKeymapItem: typ.TypeAlias = typ.Any  ## TODO: Better Type
 BLPropFlag: typ.TypeAlias = typ.Literal[

src/blender_maxwell/contracts/operator_types.py

@@ -34,6 +34,9 @@ class OperatorType(enum.StrEnum):
 
 	GeoNodesToStructureNode = enum.auto()
 
+	# Socket: GeoNodesSocket
+	SocketGeoNodesReset = enum.auto()
+
 	# Socket: Tidy3DCloudTask
 	SocketCloudAuthenticate = enum.auto()
 	SocketReloadCloudFolderList = enum.auto()

src/blender_maxwell/node_trees/maxwell_sim_nodes/contracts/bl_socket_types.py

@@ -37,11 +37,41 @@ class BLSocketInfo:
 	is_preview: bool
 	socket_type: SocketType | None
 	size: spux.NumberSize1D | None
+	mathtype: spux.MathType | None
 	physical_type: spux.PhysicalType | None
 	default_value: spux.ScalarUnitlessRealExpr
 
 	bl_isocket_identifier: spux.ScalarUnitlessRealExpr
 
+	def encode(
+		self, raw_value: typ.Any, unit_system: spux.UnitSystem | None
+	) -> typ.Any:
+		"""Encode a raw value, given a unit system, to be directly writable to a node socket.
+
+		This encoded form is also guaranteed to support writing to a node socket via a modifier interface.
+		"""
+		# Non-Numerical: Passthrough
+		if unit_system is None or self.physical_type is None:
+			return raw_value
+
+		# Numerical: Convert to Pure Python Type
+		if (
+			unit_system is not None
+			and self.physical_type is not spux.PhysicalType.NonPhysical
+		):
+			unitless_value = spux.scale_to_unit_system(raw_value, unit_system)
+		elif isinstance(raw_value, spux.SympyType):
+			unitless_value = spux.sympy_to_python(raw_value)
+		else:
+			unitless_value = raw_value
+
+		# Coerce int -> float w/Target is Real
+		## -> The value - modifier - GN path is more strict than properties.
+		if self.mathtype is spux.MathType.Real and isinstance(unitless_value, int):
+			return float(unitless_value)
+
+		return unitless_value
+
 
 class BLSocketType(enum.StrEnum):
 	Virtual = 'NodeSocketVirtual'
@@ -85,12 +115,20 @@ class BLSocketType(enum.StrEnum):
 	def from_bl_isocket(
 		bl_isocket: bpy.types.NodeTreeInterfaceSocket,
 	) -> typ.Self:
+		"""Deduce the exact `BLSocketType` represented by an interface socket.
+
+		Interface sockets are an abstraction of what any instance of a particular node tree _will have of input sockets_ once constructed.
+		"""
 		return BLSocketType(bl_isocket.bl_socket_idname)
 
 	@staticmethod
 	def info_from_bl_isocket(
 		bl_isocket: bpy.types.NodeTreeInterfaceSocket,
 	) -> typ.Self:
+		"""Deduce all `BLSocketInfo` from an interface socket.
+
+		This is a high-level method providing a clean way to chain `BLSocketType.from_bl_isocket()` together with `self.parse()`.
+		"""
 		bl_socket_type = BLSocketType.from_bl_isocket(bl_isocket)
 		if bl_socket_type.has_support:
 			return bl_socket_type.parse(
@@ -103,13 +141,21 @@ class BLSocketType(enum.StrEnum):
 	####################
 	@property
 	def has_support(self) -> bool:
+		"""Decides whether the current `BLSocketType` is explicitly not supported.
+
+		Not all socket types make sense to represent in our node tree.
+		In general, these should be skipped.
+		"""
 		BLST = BLSocketType
 		return {
+			# Won't Fix
 			BLST.Virtual: False,
 			BLST.Geometry: False,
 			BLST.Shader: False,
 			BLST.FloatUnsigned: False,
 			BLST.IntUnsigned: False,
+			## TODO
+			BLST.Menu: False,
 		}.get(self, True)
 
 	@property
@@ -132,12 +178,36 @@ class BLSocketType(enum.StrEnum):
 		ST = SocketType
 		return {
 			# Blender
+			BLST.Image: ST.BlenderImage,
+			BLST.Material: ST.BlenderMaterial,
+			BLST.Object: ST.BlenderObject,
+			BLST.Collection: ST.BlenderCollection,
 			# Basic
-			BLST.Bool: ST.Bool,
+			BLST.Bool: ST.BlenderCollection,
+			BLST.String: ST.String,
 			# Float
-			# Array-Like
+			BLST.Float: ST.Expr,
+			BLST.FloatAngle: ST.Expr,
+			BLST.FloatDistance: ST.Expr,
+			BLST.FloatFactor: ST.Expr,
+			BLST.FloatPercentage: ST.Expr,
+			BLST.FloatTime: ST.Expr,
+			BLST.FloatTimeAbsolute: ST.Expr,
+			# Int
+			BLST.Int: ST.Expr,
+			BLST.IntFactor: ST.Expr,
+			BLST.IntPercentage: ST.Expr,
+			# Vector
 			BLST.Color: ST.Color,
-		}.get(self, ST.Expr)
+			BLST.Rotation: ST.Expr,
+			BLST.Vector: ST.Expr,
+			BLST.VectorAcceleration: ST.Expr,
+			BLST.VectorDirection: ST.Expr,
+			BLST.VectorEuler: ST.Expr,
+			BLST.VectorTranslation: ST.Expr,
+			BLST.VectorVelocity: ST.Expr,
+			BLST.VectorXYZ: ST.Expr,
+		}[self]
 
 	@property
 	def mathtype(self) -> spux.MathType | None:
@@ -240,7 +310,7 @@ class BLSocketType(enum.StrEnum):
 			BLST.FloatAngle: P.Angle,
 			BLST.FloatDistance: P.Length,
 			BLST.FloatTime: P.Time,
-			BLST.FloatTimeAbsolute: P.Time,  ## What's the difference?
+			BLST.FloatTimeAbsolute: P.Time,  ## TODO: What's the difference?
 			BLST.VectorAcceleration: P.Accel,
 			## BLST.VectorDirection: Directions are unitless (within cartesian)
 			BLST.VectorEuler: P.Angle,
@@ -291,8 +361,8 @@ class BLSocketType(enum.StrEnum):
 	def parse(
 		self, bl_default_value: typ.Any, description: str, bl_isocket_identifier: str
 	) -> BLSocketInfo:
-		# Parse the Description
+		# Unpack Description
-		## TODO: Some kind of error on invalid parse if there is also no unambiguous physical type
+		## -> TODO: Raise an kind of error on invalid parse if there is also no unambiguous physical type
 		descr_params = description.split(BL_SOCKET_DESCR_ANNOT_STRING)[0]
 		directive = (
 			_tokens[0]
@@ -300,33 +370,60 @@ class BLSocketType(enum.StrEnum):
 			else _tokens[1]
 		)
 
-		## Interpret the Description Parse
+		# Parse PhysicalType
+		## -> None if there is no appropriate MathType.
+		## -> Otherwise, prefer unambiguous - description hint - NonPhysical
+		has_physical_type = self.mathtype in [
+			spux.MathType.Integer,
+			spux.MathType.Rational,
+			spux.MathType.Real,
+			spux.MathType.Complex,
+		]
+		if has_physical_type:
 			parsed_physical_type = getattr(spux.PhysicalType, directive, None)
 			physical_type = (
 				self.unambiguous_physical_type
 				if self.unambiguous_physical_type is not None
-			else parsed_physical_type
+				else (
+					parsed_physical_type
+					if parsed_physical_type is not None
+					else spux.PhysicalType.NonPhysical
 				)
+			)
+		else:
+			physical_type = None
 
-		# Parse the Default Value
+		# Parse Default Value
+		## -> Read the Blender socket's default value and convrt it
 		if self.mathtype is not None and bl_default_value is not None:
+			# Scalar: Convert to Pure Python TYpe
 			if self.size == spux.NumberSize1D.Scalar:
 				default_value = self.mathtype.pytype(bl_default_value)
+
+			# 2D (Description Hint): Sympy Matrix
+			## -> The description hint "2D" is the trigger for this.
+			## -> Ignore the last component to get the effect of "2D".
 			elif description.startswith('2D'):
-				default_value = sp.Matrix(tuple(bl_default_value)[:2])
+				default_value = sp.ImmutableMatrix(tuple(bl_default_value)[:2])
+
+			# 3D/4D: Simple Parse to Sympy Matrix
+			## -> We don't explicitly check the size.
 			else:
-				default_value = sp.Matrix(tuple(bl_default_value))
+				default_value = sp.ImmutableMatrix(tuple(bl_default_value))
+
 		else:
+			# Non-Mathematical: Passthrough
 			default_value = bl_default_value
 
 		# Return Parsed Socket Information
 		## -> Combining directly known and parsed knowledge.
-		## -> Should contain everything needed to match the Blender socket.
+		## -> Should contain everything needed to create a socket in our tree.
 		return BLSocketInfo(
 			has_support=self.has_support,
 			is_preview=(directive == 'Preview'),
 			socket_type=self.socket_type,
 			size=self.size,
+			mathtype=self.mathtype,
 			physical_type=physical_type,
 			default_value=default_value,
 			bl_isocket_identifier=bl_isocket_identifier,

src/blender_maxwell/node_trees/maxwell_sim_nodes/managed_objs/managed_bl_mesh.py

@@ -103,8 +103,8 @@ class ManagedBLMesh(base.ManagedObj):
 		"""
 		bl_object = bpy.data.objects.get(self.name)
 		if bl_object is None:
-			log.info('%s (ManagedBLMesh): Created BLObject for Preview', bl_object.name)
 			bl_object = self.bl_object()
+			log.info('%s (ManagedBLMesh): Created BLObject for Preview', bl_object.name)
 
 		if bl_object.name not in preview_collection().objects:
 			log.info('Moving "%s" to Preview Collection', bl_object.name)

src/blender_maxwell/node_trees/maxwell_sim_nodes/managed_objs/managed_bl_modifier.py

@@ -97,6 +97,7 @@ def write_modifier_geonodes(
 	modifier_altered = False
 
 	# Alter GeoNodes Group
+	## -> Check the existing node group, replace if it differs.
 	if bl_modifier.node_group != modifier_attrs['node_group']:
 		log.info(
 			'Changing GeoNodes Modifier NodeTree from "%s" to "%s"',
@@ -106,30 +107,25 @@ def write_modifier_geonodes(
 		bl_modifier.node_group = modifier_attrs['node_group']
 		modifier_altered = True
 
-	# Alter GeoNodes Modifier Inputs
+	# Parse GeoNodes Socket Info
+	## -> TODO: Slow and hard to optimize, but very likely worth it.
 	socket_infos = bl_socket_map.info_from_geonodes(bl_modifier.node_group)
 
 	for socket_name in modifier_attrs['inputs']:
+		# Retrieve Modifier Interface ID
+		## -> iface_id translates "modifier socket" to "GN input socket".
 		iface_id = socket_infos[socket_name].bl_isocket_identifier
-		input_value = modifier_attrs['inputs'][socket_name]
 
-		if modifier_attrs['unit_system'] is not None and not isinstance(
+		# Deduce Value to Write
-			input_value, bool
+		## -> This may involve a unit system conversion.
-		):
+		## -> Special Case: Booleans do not go through unit conversion.
-			value_to_write = spux.scale_to_unit_system(
+		## -> TODO: A special case isn't clean enough.
-				input_value, modifier_attrs['unit_system']
+		bl_modifier[iface_id] = socket_infos[socket_name].encode(
+			raw_value=modifier_attrs['inputs'][socket_name],
+			unit_system=modifier_attrs['unit_system'],
 		)
-		else:
-			value_to_write = input_value
-
-		# Edge Case: int -> float
-		if isinstance(bl_modifier[iface_id], float) and isinstance(value_to_write, int):
-			bl_modifier[iface_id] = float(value_to_write)
-		else:
-			bl_modifier[iface_id] = value_to_write
-
 		modifier_altered = True
-	## TODO: More fine-grained alterations
+		## TODO: More fine-grained alterations?
 
 	return modifier_altered  # noqa: RET504
 

src/blender_maxwell/node_trees/maxwell_sim_nodes/node_tree.py

@@ -435,6 +435,7 @@ def initialize_sim_tree_node_link_cache(_):
 	"""Whenever a file is loaded, create/regenerate the NodeLinkCache in all trees."""
 	for node_tree in bpy.data.node_groups:
 		if node_tree.bl_idname == 'MaxwellSimTree':
+			log.debug('%s: Initializing NodeLinkCache for NodeTree', str(node_tree))
 			node_tree.on_load()
 
 
@@ -450,13 +451,26 @@ def populate_missing_persistence(_) -> None:
 		for _node_tree in bpy.data.node_groups
 		if _node_tree.bl_idname == ct.TreeType.MaxwellSim.value and _node_tree.is_active
 	]:
+		log.debug(
+			'%s: Regenerating Dynamic Field Persistance for NodeTree nodes/sockets',
+			str(node_tree),
+		)
 		# Iterate over MaxwellSim Nodes
 		# -> Excludes ex. frame and reroute nodes.
 		for node in [_node for _node in node_tree.nodes if hasattr(_node, 'node_type')]:
+			log.debug(
+				'-> %s: Regenerating Dynamic Field Persistance for Node',
+				str(node),
+			)
 			node.regenerate_dynamic_field_persistance()
 			for bl_sockets in [node.inputs, node.outputs]:
 				for bl_socket in bl_sockets:
+					log.debug(
+						'|-> %s: Regenerating Dynamic Field Persistance for Socket',
+						str(bl_socket),
+					)
 					bl_socket.regenerate_dynamic_field_persistance()
+	log.debug('Regenerated All Dynamic Field Persistance')
 
 
 ####################

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/base.py

@@ -737,6 +737,14 @@ class MaxwellSimNode(bpy.types.Node, bl_instance.BLInstance):
 			socket_name: The input socket that was altered, if any, in order to trigger this event.
 			pop_name: The property that was altered, if any, in order to trigger this event.
 		"""
+		# log.debug(
+		# '%s: Triggered Event %s (socket_name=%s, socket_kinds=%s, prop_name=%s)',
+		# self.sim_node_name,
+		# event,
+		# str(socket_name),
+		# str(socket_kinds),
+		# str(prop_name),
+		# )
 		# Outflow Socket Kinds
 		## -> Something has happened!
 		## -> The effect is yet to be determined...
@@ -815,9 +823,9 @@ class MaxwellSimNode(bpy.types.Node, bl_instance.BLInstance):
 		for event_method in triggered_event_methods:
 			stop_propagation |= event_method.stop_propagation
 			# log.critical(
-			# '$[%s] [%s %s %s %s] Running: (%s)',
+			# '%s: Running %s',
 			# self.sim_node_name,
-			# event_method.callback_info,
+			# str(event_method.callback_info),
 			# )
 			event_method(self)
 

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/structures/geonodes_structure.py

@@ -43,8 +43,6 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 		'Medium': sockets.MaxwellMediumSocketDef(),
 		'Center': sockets.ExprSocketDef(
 			size=spux.NumberSize1D.Vec3,
-			mathtype=spux.MathType.Real,
-			physical_type=spux.PhysicalType.Length,
 			default_unit=spu.micrometer,
 			default_value=sp.Matrix([0, 0, 0]),
 		),
@@ -54,7 +52,6 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 	}
 
 	managed_obj_types: typ.ClassVar = {
-		'mesh': managed_objs.ManagedBLMesh,
 		'modifier': managed_objs.ManagedBLModifier,
 	}
 
@@ -64,7 +61,7 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 	@events.computes_output_socket(
 		'Structure',
 		input_sockets={'Medium'},
-		managed_objs={'mesh'},
+		managed_objs={'modifier'},
 	)
 	def compute_structure(
 		self,
@@ -74,7 +71,7 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 		"""Computes a triangle-mesh based Tidy3D structure, by manually copying mesh data from Blender to a `td.TriangleMesh`."""
 		## TODO: mesh_as_arrays might not take the Center into account.
 		## - Alternatively, Tidy3D might have a way to transform?
-		mesh_as_arrays = managed_objs['mesh'].mesh_as_arrays
+		mesh_as_arrays = managed_objs['modifier'].mesh_as_arrays
 		return td.Structure(
 			geometry=td.TriangleMesh.from_vertices_faces(
 				mesh_as_arrays['verts'],
@@ -84,71 +81,28 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 		)
 
 	####################
-	# - Events: Preview Active Changed
+	# - UI
 	####################
-	@events.on_value_changed(
+	def draw_label(self) -> None:
-		prop_name='preview_active',
+		"""Show the extracted data (if any) in the node's header label.
-		props={'preview_active'},
-		managed_objs={'mesh'},
-	)
-	def on_preview_changed(self, props) -> None:
-		"""Enables/disables previewing of the GeoNodes-driven mesh, regardless of whether a particular GeoNodes tree is chosen."""
-		mesh = managed_objs['mesh']
 
-		# Push Preview State to Managed Mesh
+		Notes:
-		if props['preview_active']:
+			Called by Blender to determine the text to place in the node's header.
-			mesh.show_preview()
-		else:
-			mesh.hide_preview()
-
-	####################
-	# - Events: GN Input Changed
-	####################
-	@events.on_value_changed(
-		socket_name={'Center'},
-		any_loose_input_socket=True,
-		# Pass Data
-		managed_objs={'mesh', 'modifier'},
-		input_sockets={'Center', 'GeoNodes'},
-		all_loose_input_sockets=True,
-		unit_systems={'BlenderUnits': ct.UNITS_BLENDER},
-		scale_input_sockets={'Center': 'BlenderUnits'},
-	)
-	def on_input_socket_changed(
-		self, input_sockets, loose_input_sockets, unit_systems
-	) -> None:
-		"""Pushes any change in GeoNodes-bound input sockets to the GeoNodes modifier.
-
-		Also pushes the `Center:Value` socket to govern the object's center in 3D space.
 		"""
-		geonodes = input_sockets['GeoNodes']
+		geonodes = self._compute_input('GeoNodes')
-		has_geonodes = not ct.FlowSignal.check(geonodes)
+		if geonodes is None:
+			return self.bl_label
 
-		if has_geonodes:
+		return f'Structure: {self.sim_node_name}'
-			mesh = managed_objs['mesh']
-			modifier = managed_objs['modifier']
-			center = input_sockets['Center']
-			unit_system = unit_systems['BlenderUnits']
-
-			# Push Loose Input Values to GeoNodes Modifier
-			modifier.bl_modifier(
-				mesh.bl_object(location=center),
-				'NODES',
-				{
-					'node_group': geonodes,
-					'inputs': loose_input_sockets,
-					'unit_system': unit_system,
-				},
-			)
 
 	####################
-	# - Events: GN Tree Changed
+	# - Events: Swapped GN Node Tree
 	####################
 	@events.on_value_changed(
 		socket_name={'GeoNodes'},
-		# Pass Data
+		# Loaded
-		managed_objs={'mesh', 'modifier'},
+		managed_objs={'modifier'},
-		input_sockets={'GeoNodes', 'Center'},
+		input_sockets={'GeoNodes'},
 	)
 	def on_input_changed(
 		self,
@@ -157,12 +111,9 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 	) -> None:
 		"""Declares new loose input sockets in response to a new GeoNodes tree (if any)."""
 		geonodes = input_sockets['GeoNodes']
-		has_geonodes = not ct.FlowSignal.check(geonodes)
+		has_geonodes = not ct.FlowSignal.check(geonodes) and geonodes is not None
 
 		if has_geonodes:
-			mesh = managed_objs['mesh']
-			modifier = managed_objs['modifier']
-
 			# Fill the Loose Input Sockets
 			## -> The SocketDefs contain the default values from the interface.
 			log.info(
@@ -176,9 +127,59 @@ class GeoNodesStructureNode(base.MaxwellSimNode):
 
 		elif self.loose_input_sockets:
 			self.loose_input_sockets = {}
+			managed_objs['modifier'].free()
 
-			if modifier.name in mesh.bl_object().modifiers.keys().copy():
+	####################
-				modifier.free_from_bl_object(mesh.bl_object())
+	# - Events: Preview
+	####################
+	@events.on_value_changed(
+		# Trigger
+		prop_name='preview_active',
+		# Loaded
+		managed_objs={'modifier'},
+		props={'preview_active'},
+	)
+	def on_preview_changed(self, managed_objs, props):
+		if props['preview_active']:
+			managed_objs['modifier'].show_preview()
+		else:
+			managed_objs['modifier'].hide_preview()
+
+	@events.on_value_changed(
+		# Trigger
+		socket_name={'Center', 'GeoNodes'},  ## MUST run after on_input_changed
+		any_loose_input_socket=True,
+		# Loaded
+		managed_objs={'modifier'},
+		input_sockets={'Center', 'GeoNodes'},
+		all_loose_input_sockets=True,
+		unit_systems={'BlenderUnits': ct.UNITS_BLENDER},
+		scale_input_sockets={'Center': 'BlenderUnits'},
+	)
+	def on_input_socket_changed(
+		self, managed_objs, input_sockets, loose_input_sockets, unit_systems
+	) -> None:
+		"""Pushes any change in GeoNodes-bound input sockets to the GeoNodes modifier.
+
+		Warnings:
+			MUST be placed lower than `on_input_changed`, so it runs afterwards whenever the `GeoNodes` tree is changed.
+
+		Also pushes the `Center:Value` socket to govern the object's center in 3D space.
+		"""
+		geonodes = input_sockets['GeoNodes']
+		has_geonodes = not ct.FlowSignal.check(geonodes) and geonodes is not None
+
+		if has_geonodes:
+			# Push Loose Input Values to GeoNodes Modifier
+			managed_objs['modifier'].bl_modifier(
+				'NODES',
+				{
+					'node_group': geonodes,
+					'inputs': loose_input_sockets,
+					'unit_system': unit_systems['BlenderUnits'],
+				},
+				location=input_sockets['Center'],
+			)
 
 
 ####################

src/blender_maxwell/node_trees/maxwell_sim_nodes/nodes/structures/primitives/box_structure.py

@@ -83,7 +83,7 @@ class BoxStructureNode(base.MaxwellSimNode):
 		)
 
 	####################
-	# - Preview
+	# - Events: Preview
 	####################
 	@events.on_value_changed(
 		# Trigger

src/blender_maxwell/node_trees/maxwell_sim_nodes/sockets/blender/geonodes.py

@@ -14,30 +14,40 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import typing as typ
+
 import bpy
+import sympy as sp
+import sympy.physics.units as spu
+import tidy3d as td
+
+from blender_maxwell.assets.geonodes import GeoNodes, import_geonodes
+from blender_maxwell.utils import bl_cache, logger
+from blender_maxwell.utils import extra_sympy_units as spux
 
 from ... import contracts as ct
 from .. import base
 
+log = logger.get(__name__)
+
 
 ####################
 # - Operators
 ####################
 class BlenderMaxwellResetGeoNodesSocket(bpy.types.Operator):
-	bl_idname = 'blender_maxwell.reset_geo_nodes_socket'
+	"""Simulate a change to the geometry nodes group of the attached `GeoNodes` socket.
-	bl_label = 'Reset GeoNodes Socket'
 
-	node_tree_name: bpy.props.StringProperty(name='Node Tree Name')
+	This causes updates to the GN group (ex. internal logic) to be immediately caught.
-	node_name: bpy.props.StringProperty(name='Node Name')
+	"""
-	socket_name: bpy.props.StringProperty(name='Socket Name')
+
+	bl_idname = ct.OperatorType.SocketGeoNodesReset
+	bl_label = 'Reset GeoNodes Group'
 
 	def execute(self, context):
-		node_tree = bpy.data.node_groups[self.node_tree_name]
+		bl_socket = context.socket
-		node = node_tree.nodes[self.node_name]
-		socket = node.inputs[self.socket_name]
 
 		# Report as though the GeoNodes Tree Changed
-		socket.on_prop_changed('raw_value', context)
+		bl_socket.on_prop_changed('raw_value', context)
 
 		return {'FINISHED'}
 
@@ -52,35 +62,18 @@ class BlenderGeoNodesBLSocket(base.MaxwellSimSocket):
 	####################
 	# - Properties
 	####################
-	raw_value: bpy.props.PointerProperty(
+	raw_value: bpy.types.NodeTree = bl_cache.BLField(
-		name='Blender GeoNodes Tree',
+		bltype_poll=lambda self, obj: self.filter_gn_trees(obj)
-		description='Represents a Blender GeoNodes Tree',
-		type=bpy.types.NodeTree,
-		poll=(lambda self, obj: obj.bl_idname == 'GeometryNodeTree'),
-		update=(lambda self, context: self.on_prop_changed('raw_value', context)),
 	)
 
-	####################
+	def filter_gn_trees(self, obj: ct.BLIDStruct) -> bool:
-	# - UI
+		return obj.bl_idname == 'GeometryNodeTree' and not obj.name.startswith('_')
-	####################
-	# def draw_label_row(self, label_col_row, text):
-	# label_col_row.label(text=text)
-	# if not self.raw_value: return
-	#
-	# op = label_col_row.operator(
-	# BlenderMaxwellResetGeoNodesSocket.bl_idname,
-	# text="",
-	# icon="FILE_REFRESH",
-	# )
-	# op.socket_name = self.name
-	# op.node_name = self.node.name
-	# op.node_tree_name = self.node.id_data.name
 
 	####################
 	# - UI
 	####################
 	def draw_value(self, col: bpy.types.UILayout) -> None:
-		col.prop(self, 'raw_value', text='')
+		col.prop(self, self.blfields['raw_value'], text='')
 
 	####################
 	# - Default Value

src/blender_maxwell/utils/bl_cache/bl_field.py

@@ -36,6 +36,7 @@ StringPropSubType: typ.TypeAlias = typ.Literal[
 	'FILE_PATH', 'DIR_PATH', 'FILE_NAME', 'BYTE_STRING', 'PASSWORD', 'NONE'
 ]
 
+PollMethod: typ.TypeAlias = typ.Callable[[bl_instance.BLInstance, typ.Any], bool]
 StrMethod: typ.TypeAlias = typ.Callable[
 	[bl_instance.BLInstance, bpy.types.Context, str], list[tuple[str, str]]
 ]
@@ -72,8 +73,7 @@ class BLField:
 		float_prec: int | None = None,
 		str_secret: bool | None = None,
 		path_type: typ.Literal['dir', 'file'] | None = None,
-		# blptr_type: typ.Any | None = None,  ## A Blender ID type
+		bltype_poll: PollMethod | None = None,
-		## TODO: Test/Implement
 		## Dynamic
 		str_cb: StrMethod | None = None,
 		enum_cb: EnumMethod | None = None,
@@ -110,6 +110,10 @@ class BLField:
 				Only meaningful for `pathlib.Path` properties.
 				**NOTE**: No effort is made to make paths portable between operating systems.
 				Use with care.
+			bltype_poll: User-provided method for filtering selectable datablocks.
+				Whenever the annotated type is `ct.BLIDStruct`, it may be desirable to constrain which datablocks the user should be able to select.
+				This allows doing so.
+				**NOTE**: The method will be run very often, and must therefore be cheap.
 			str_cb: Method used to determine all valid strings, which presents to the user as a fuzzy-style search dropdown.
 				Only meaningful for `str` properties.
 				Results are not persisted, and must therefore re-run when reloading the file.
@@ -121,12 +125,6 @@ class BLField:
 			cb_depends_on: Declares that `str_cb` / `enum_cb` should be regenerated whenever any of the given property names change.
 				This allows fully automating the invocation of `Signal.ResetEnumItems` / `Signal.ResetStrSearch` in common cases.
 		"""
-		log.debug(
-			'Initializing BLField (default_value=%s, use_prop_update=%s)',
-			str(default_value),
-			str(use_prop_update),
-		)
-
 		self.use_dynamic_enum = enum_cb is not None
 		self.use_str_search = str_cb is not None
 
@@ -143,7 +141,7 @@ class BLField:
 			'step': float_step,
 			'precision': float_prec,
 			# BLPointer: ID Type
-			#'blptr_type': blptr_type,
+			'bltype_poll': bltype_poll,
 			# Str | Path | Enum: Flag Setters
 			'str_secret': str_secret,
 			'path_type': path_type,
@@ -222,6 +220,14 @@ class BLField:
 			)
 			self.bl_prop_str_search.init_bl_type(owner)
 
+		log.debug(
+			'Initialized BLField "%s" (prop_type=%s, type=%s, default_value=%s)',
+			str(self.bl_prop.name),
+			str(self.bl_prop.bl_prop_type),
+			str(self.bl_prop.prop_type),
+			str(self.bl_prop.default_value),
+		)
+
 	def __get__(
 		self,
 		bl_instance: bl_instance.BLInstance | None,
@@ -290,6 +296,9 @@ class BLField:
 
 		# Reset Enum Items
 		elif value is Signal.ResetEnumItems:
+			if self.bl_prop_enum_items is None:
+				return
+
 			# Retrieve Old Items
 			## -> This is verbatim what is being persisted, currently.
 			## -> len(0): Manually replaced w/fallback to guarantee >=len(1)
@@ -356,6 +365,9 @@ class BLField:
 
 		# Reset Str Search
 		elif value is Signal.ResetStrSearch:
+			if self.bl_prop_str_search is None:
+				return
+
 			self.bl_prop_str_search.invalidate_nonpersist(bl_instance)
 
 		# General __set__

src/blender_maxwell/utils/bl_cache/bl_prop.py

@@ -173,6 +173,10 @@ class BLProp:
 	def read_nonpersist(self, bl_instance: bl_instance.BLInstance | None) -> typ.Any:
 		"""Read the non-persistent cache value for this property.
 
+		Notes:
+			**Never reads cached BLPointers**; invokes `self.read()` instead.
+			`BLPointer`s must align perfectly with Blender's internal logic, and as such, the cache cannot get involved, else we risk access-after-free crashes.
+
 		Returns:
 			Generally, the cache value, with two exceptions.
 
@@ -184,6 +188,8 @@ class BLProp:
 			- `Signal.CacheEmpty`: When the cache has no entry.
 				A good idea might be to fill it immediately with `self.write_nonpersist(bl_instance)`.
 		"""
+		if self.bl_prop_type is BLPropType.BLPointer:
+			return self.read(bl_instance)
 		return managed_cache.read(
 			bl_instance,
 			self.bl_name,
@@ -215,11 +221,17 @@ class BLProp:
 			use_nonpersist=False,
 			use_persist=True,
 		)
+		if self.bl_prop_type is BLPropType.BLPointer:
+			return
+
 		self.write_nonpersist(bl_instance, value)
 
 	def write_nonpersist(
 		self, bl_instance: bl_instance.BLInstance, value: typ.Any
 	) -> None:
+		if self.bl_prop_type is BLPropType.BLPointer:
+			return  ## We can't always write here, so we can only do nothing.
+
 		managed_cache.write(
 			bl_instance,
 			self.bl_name,
@@ -229,6 +241,9 @@ class BLProp:
 		)
 
 	def invalidate_nonpersist(self, bl_instance: bl_instance.BLInstance | None) -> None:
+		if self.bl_prop_type is BLPropType.BLPointer:
+			return
+
 		managed_cache.invalidate_nonpersist(
 			bl_instance,
 			self.bl_name,

src/blender_maxwell/utils/bl_cache/bl_prop_type.py

@@ -82,6 +82,10 @@ def _is_strenum(T: type) -> bool:  # noqa: N803
 	return inspect.isclass(T) and issubclass(T, enum.StrEnum)
 
 
+def _is_bl_id_struct(T: type) -> bool:  # noqa: N803
+	return T in BLIDStructs
+
+
 ####################
 # - Blender Property Type
 ####################
@@ -323,7 +327,7 @@ class BLPropType(enum.StrEnum):
 			BPT.SingleDynEnum: ['enum_dynamic'],
 			BPT.SetDynEnum: ['enum_dynamic'],
 			# Special
-			BPT.BLPointer: ['blptr_type'],
+			BPT.BLPointer: [],
 			BPT.Serialized: [],
 		}[self]
 
@@ -365,6 +369,12 @@ class BLPropType(enum.StrEnum):
 
 		# Define Information -> KWArg Getter
 		def g_kwarg(name: str, force_key: str | None = None):
+			"""Retrieve a dictionary mapping a name to its `prop_info[name]` value.
+
+			If `name` is not defined in `prop_info`, then return an empty dictionary.
+
+			If `force_key` is set, then use it as to override `name` as the key when returning the dictionary.
+			"""
 			key = force_key if force_key is not None else name
 			return {key: prop_info[name]} if prop_info.get(name) is not None else {}
 
@@ -482,10 +492,13 @@ class BLPropType(enum.StrEnum):
 
 			# BLPointer
 			case BPT.BLPointer:
-				kwargs |= encoded_default
-
 				# BLPointer: ID Type
-				kwargs |= g_kwarg('blptr_type', force_key='type')
+				## -> This is the type of datablock that will be selectable.
+				kwargs |= {'type': obj_type}
+
+				# BLPointer: Poll Method
+				## -> This allows the user filter selectable datablocks.
+				kwargs |= g_kwarg('bltype_poll', force_key='poll')
 
 			# BLPointer
 			case BPT.Serialized:
@@ -573,7 +586,7 @@ class BLPropType(enum.StrEnum):
 				return {str(v) for v in value}
 
 			# BLPointer: Don't Alter
-			case BPT.BLPointer if value in BLIDStructs or value is None:
+			case BPT.BLPointer:
 				return value
 
 			# Serialized: Serialize To UTF-8
@@ -662,7 +675,7 @@ class BLPropType(enum.StrEnum):
 
 			# BLPointer
 			## -> None is always valid when it comes to BLPointers.
-			case BPT.BLPointer if raw_value in BLIDStructs or raw_value is None:
+			case BPT.BLPointer:
 				return raw_value
 
 			# Serialized: Deserialize the Argument
@@ -748,7 +761,7 @@ class BLPropType(enum.StrEnum):
 			return BPT.SetEnum
 
 		# Match BLPointers
-		if obj_type in BLIDStructs:
+		if _is_bl_id_struct(obj_type):
 			return BPT.BLPointer
 
 		# Fallback: Serializable Object

src/blender_maxwell/utils/extra_sympy_units.py

@@ -1285,6 +1285,7 @@ UnitSystem: typ.TypeAlias = dict[PhysicalType, Unit]
 
 _PT = PhysicalType
 UNITS_SI: UnitSystem = {
+	_PT.NonPhysical: None,
 	# Global
 	_PT.Time: spu.second,
 	_PT.Angle: spu.radian,
@@ -1396,7 +1397,7 @@ def strip_unit_system(sp_obj: SympyExpr, unit_system: UnitSystem) -> SympyExpr:
 	Notes:
 		You should probably use `scale_to_unit_system()` or `convert_to_unit_system()`.
 	"""
-	return sp_obj.subs({unit: 1 for unit in unit_system.values()})
+	return sp_obj.subs({unit: 1 for unit in unit_system.values() if unit is not None})
 
 
 def scale_to_unit_system(