feat: Add Bioxel asset catalog and layer management functionality

- Introduced a new asset catalog definition file for Blender to manage Bioxel assets.
- Implemented layer caching and snapshot functionality in `layer.py`, allowing for VDB file generation and low-resolution snapshots.
- Created node management functions in `node.py` for handling Bioxel nodes within Blender's Geometry Node Editor.
- Added an operator to extract mesh data from selected nodes in `structure.py`.
- Developed UI panels in `panels.py` for layer management, including import options and layer library display.

src/bioxelnodes/node.py

@@ -0,0 +1,149 @@
+from pathlib import Path
+import bpy
+
+# LookupError replaced with built-in LookupError
+from .constants import LATEST_NODE_LIB_PATH
+
+
+def move_node_to_node(node, target_node, offset=(0, 0)):
+    node.location.x = target_node.location.x + offset[0]
+    node.location.y = target_node.location.y + offset[1]
+
+
+def move_node_between_nodes(node, target_nodes, offset=(0, 0)):
+    xs = []
+    ys = []
+    for target_node in target_nodes:
+        xs.append(target_node.location.x)
+        ys.append(target_node.location.y)
+
+    node.location.x = sum(xs) / len(xs) + offset[0]
+    node.location.y = sum(ys) / len(ys) + offset[1]
+
+
+def get_node_type(node):
+    node_type = type(node).__name__
+    if node_type == "GeometryNodeGroup":
+        node_type = node.node_tree.name
+
+    return node_type
+
+
+def get_nodes_by_type(node_group, type_name: str):
+    return [node for node in node_group.nodes if get_node_type(node) == type_name]
+
+
+def get_node_tree(node_type: str, use_link=True):
+    try:
+        return bpy.data.node_groups[node_type]
+    except KeyError:
+        lib_path_str = str(LATEST_NODE_LIB_PATH)
+        with bpy.data.libraries.load(lib_path_str, link=use_link, relative=True) as (
+            data_from,
+            data_to,
+        ):
+            data_to.node_groups = [
+                n for n in data_from.node_groups if n == node_type]
+        node_tree = data_to.node_groups[0]
+
+        if node_tree is None:
+            raise LookupError("No custom node found")
+
+        return node_tree
+
+
+def assign_node_tree(node, node_tree):
+    node.node_tree = node_tree
+    node.width = 200.0
+    node.name = node_tree.name
+    return node
+
+
+def add_node_to_graph(node_name: str, node_group, node_label=None, use_link=True):
+    node_type = f"O {node_name}"
+    node_label = node_label or node_name
+
+    # Deselect all nodes first
+    for node in node_group.nodes:
+        if node.select:
+            node.select = False
+
+    node_tree = get_node_tree(node_type, use_link)
+    node = node_group.nodes.new("GeometryNodeGroup")
+    assign_node_tree(node, node_tree)
+
+    node.label = node_label
+    node.show_options = False
+    bpy.ops.node.view_selected()
+    return node
+
+
+def get_output_node(node_group):
+    try:
+        output_node = get_nodes_by_type(node_group, "NodeGroupOutput")[0]
+    except:
+        output_node = node_group.nodes.new("NodeGroupOutput")
+
+    return output_node
+
+
+def add_bioxel_node(name: str):
+    # bpy.ops.node.add_group_asset(
+    #     asset_library_type="CUSTOM",
+    #     asset_library_identifier = "O Bioxel",
+    #     relative_asset_identifier = "NodeTreO Crop Layer"
+    # )
+    # bpy.ops.node.add_group_asset(
+    #     asset_library_type="CUSTOM",
+    #     asset_library_identifier="O Bioxel",
+    #     relative_asset_identifier="Nodes.blend\\NodeTree\\O Render Structure"
+    # )
+
+    try:
+        node_tree = bpy.data.node_groups[name]
+    except KeyError:
+        bpy.ops.object.modifier_add_node_group(
+            asset_library_type="CUSTOM",
+            asset_library_identifier="O Bioxel",
+            relative_asset_identifier=f"Nodes.blend\\NodeTree\\{name}",
+        )
+        bpy.ops.object.modifier_remove(modifier=name)
+        try:
+            node_tree = bpy.data.node_groups[name]
+        except Exception as e:
+            raise e
+
+    bpy.ops.node.add_node(
+        "INVOKE_DEFAULT", type="GeometryNodeGroup", use_transform=True
+    )
+
+    node = bpy.context.active_node
+    node.node_tree = node_tree
+    node.show_options = False
+
+    return bpy.context.active_node
+
+
+def get_layer_nodes(node_group):
+    """Return all O Layer nodes in the given node_tree."""
+    return [
+        n
+        for n in node_group.nodes
+        if n.bl_idname == "GeometryNodeGroup"
+        and getattr(n, "node_tree", None)
+        and n.node_tree.name.startswith("O Layer")
+    ]
+
+
+def get_main_node_group(context):
+    space = getattr(context, "space_data", None) or getattr(
+        context, "space", None)
+    if not space:
+        return None
+    node_tree = getattr(space, "node_tree", None)
+    if not node_tree:
+        return None
+    # accept GeometryNodeTree by bl_idname or class name for compatibility
+    if getattr(node_tree, "bl_idname", "") == "GeometryNodeTree" or node_tree.__class__.__name__ == "GeometryNodeTree":
+        return node_tree
+    return None