Add cutout shell and volume node assets for depth volume processing

- Implemented `cutout_shell.py` to build front normals and shell positions for balloon geometry.
- Created `cutout_volume.py` to establish smooth center fields and manage balloon surface attributes.
- Introduced `pisa_sr_export.py` for exporting PiSA-SR components with dependencies and asset finalization.

tools/node_assets/cutout_depth_surface.py

@@ -8,7 +8,6 @@ TEMPORARY_ATTRIBUTES = {
     "camera": ("FLOAT_VECTOR", "POINT"),
     "surface_position": ("FLOAT_VECTOR", "POINT"),
     "source_vertex": ("INT", "POINT"),
-    "wall_layers": ("FLOAT", "POINT"),
 }
 
 
@@ -50,7 +49,7 @@ def _math(group, operation, a, b=None):
     return node.outputs[0]
 
 
-def split_depth_surface(group, geometry, image, strength, uniform, depth_scale):
+def split_depth_surface(group, geometry, image, strength, uniform):
     """Keep each face's camera sample on its own corners before splitting."""
     nodes, links = group.nodes, group.links
     uv = nodes.new("GeometryNodeInputNamedAttribute")
@@ -93,7 +92,6 @@ def split_depth_surface(group, geometry, image, strength, uniform, depth_scale):
         links.new(center, distance.inputs[index])
     delta = _math(group, "ABSOLUTE", _math(group, "SUBTRACT", *depths))
     scaled = _math(group, "MULTIPLY", delta, uniform)
-    scaled = _math(group, "MULTIPLY", scaled, _math(group, "ABSOLUTE", depth_scale))
     # Cross multiplication avoids division and stays invariant under uniform scaling.
     selected = _math(
         group,
@@ -171,7 +169,7 @@ def store_surface_camera(group, geometry, original, strength):
 
 
 def thicken_depth_surface(group, geometry, thickness):
-    """Connect caps and wall rings by source vertex and layer identity."""
+    """Connect caps with single quads by source vertex and cap identity."""
     nodes, links = group.nodes, group.links
     position = nodes.new("GeometryNodeInputPosition")
     geometry = _store(group, geometry, "surface_position", position.outputs[0])
@@ -186,33 +184,7 @@ def thicken_depth_surface(group, geometry, thickness):
     geometry = _store(
         group, sheet.outputs["Geometry"], "source_vertex", index.outputs[0]
     )
-    edge = nodes.new("GeometryNodeInputMeshEdgeVertices")
-    length = nodes.new("ShaderNodeVectorMath")
-    length.operation = "DISTANCE"
-    links.new(edge.outputs["Position 1"], length.inputs[0])
-    links.new(edge.outputs["Position 2"], length.inputs[1])
-    neighbors = nodes.new("GeometryNodeInputMeshEdgeNeighbors")
-    statistics = nodes.new("GeometryNodeAttributeStatistic")
-    statistics.domain = "EDGE"
-    statistics.data_type = "FLOAT"
-    links.new(geometry, statistics.inputs["Geometry"])
-    links.new(
-        _math(group, "COMPARE", neighbors.outputs["Face Count"], 1.0),
-        statistics.inputs["Selection"],
-    )
-    links.new(length.outputs["Value"], statistics.inputs["Attribute"])
-    count = _math(
-        group,
-        "CEIL",
-        _math(
-            group,
-            "DIVIDE",
-            thickness,
-            _math(group, "MAXIMUM", statistics.outputs["Median"], 1e-6),
-        ),
-    )
-    count = _math(group, "MINIMUM", _math(group, "MAXIMUM", count, 1.0), 128.0)
-    saved = _store(group, geometry, "wall_layers", count)
+    saved = geometry
 
     # Weld in an integer identity grid, never in scene coordinates. Nearby cuts
     # retain distinct IDs; copies of one rim vertex share the same ID and layer.
@@ -224,41 +196,26 @@ def thicken_depth_surface(group, geometry, thickness):
         links.new(_read(group, "source_vertex"), part.inputs[0])
         links.new(part.outputs[0], identity.inputs[axis])
 
-    repeat_output = nodes.new("GeometryNodeRepeatOutput")
-    repeat_input = nodes.new("GeometryNodeRepeatInput")
-    repeat_input.pair_with_output(repeat_output)
-    repeat_output.repeat_items.clear()
-    repeat_output.repeat_items.new("GEOMETRY", "Geometry")
-    repeat_output.repeat_items.new("GEOMETRY", "Sides")
-    links.new(count, repeat_input.inputs["Iterations"])
-    links.new(saved, repeat_input.inputs["Geometry"])
     extrude = nodes.new("GeometryNodeExtrudeMesh")
     extrude.mode = "FACES"
     extrude.inputs["Individual"].default_value = False
     extrusion_offset = nodes.new("ShaderNodeCombineXYZ")
     extrusion_offset.inputs["Z"].default_value = -1.0
     links.new(extrusion_offset.outputs[0], extrude.inputs["Offset"])
-    links.new(repeat_input.outputs["Geometry"], extrude.inputs["Mesh"])
+    links.new(saved, extrude.inputs["Mesh"])
     sides = nodes.new("GeometryNodeSeparateGeometry")
     sides.domain = "FACE"
     links.new(extrude.outputs["Mesh"], sides.inputs["Geometry"])
     links.new(extrude.outputs["Side"], sides.inputs["Selection"])
-    join_sides = nodes.new("GeometryNodeJoinGeometry")
-    links.new(repeat_input.outputs["Sides"], join_sides.inputs["Geometry"])
-    links.new(sides.outputs["Selection"], join_sides.inputs["Geometry"])
-    links.new(sides.outputs["Inverted"], repeat_output.inputs["Geometry"])
-    links.new(join_sides.outputs["Geometry"], repeat_output.inputs["Sides"])
     offset = nodes.new("ShaderNodeCombineXYZ")
-    links.new(
-        _math(group, "MULTIPLY", _read(group, "wall_layers"), -1.0), offset.inputs["Z"]
-    )
+    offset.inputs["Z"].default_value = -1.0
     back = nodes.new("GeometryNodeSetPosition")
     links.new(saved, back.inputs["Geometry"])
     links.new(offset.outputs[0], back.inputs["Offset"])
     flip_back = nodes.new("GeometryNodeFlipFaces")
     links.new(back.outputs["Geometry"], flip_back.inputs["Mesh"])
     flip_sides = nodes.new("GeometryNodeFlipFaces")
-    links.new(repeat_output.outputs["Sides"], flip_sides.inputs["Mesh"])
+    links.new(sides.outputs["Selection"], flip_sides.inputs["Mesh"])
     join = nodes.new("GeometryNodeJoinGeometry")
     for value in (
         saved,
@@ -274,12 +231,11 @@ def thicken_depth_surface(group, geometry, thickness):
     merge.inputs["Distance"].default_value = 0.1
     links.new(encoded.outputs["Geometry"], merge.inputs["Geometry"])
     displacement = nodes.new("ShaderNodeCombineXYZ")
-    step = _math(group, "DIVIDE", thickness, _read(group, "wall_layers"))
     layer_position = nodes.new("GeometryNodeInputPosition")
     layer_axes = nodes.new("ShaderNodeSeparateXYZ")
     links.new(layer_position.outputs[0], layer_axes.inputs[0])
     links.new(
-        _math(group, "MULTIPLY", layer_axes.outputs["Z"], step),
+        _math(group, "MULTIPLY", layer_axes.outputs["Z"], thickness),
         displacement.inputs["Z"],
     )
     restored = nodes.new("ShaderNodeVectorMath")