Problem

When activating a plan view drawing (bim.activate_drawing) after previously
activating a reflected ceiling plan (RCP) drawing — or vice versa — certain
elements would be hidden from the scene even though they belong to that storey
level. In the reported case, an IfcLightFixture with both PLAN_VIEW and
REFLECTED_PLAN_VIEW representations was invisible after switching between the
two drawing types.

Root Cause

activate_drawing calls get_drawing_elements, which calls
get_elements_in_camera_view to determine which objects fall within the
camera's frustum. The frustum test in is_in_camera_view used obj.bound_box
— the bounding box of the currently active Blender mesh — to determine
whether an element intersects the camera.

The problem is that activate_drawing switches each element's active
representation to match the target view after the camera frustum test. So
when switching from an RCP drawing to a plan view drawing:

1. The element's active mesh is the REFLECTED_PLAN_VIEW geometry (ceiling
   level, e.g. local z ≈ +1.2 m above the element origin).
2. The plan view camera looks downward from z = 1.6 m world. The camera frustum
   in camera-local space spans z ∈ [−10, −0.002].
3. The ceiling-level mesh transforms to positive z in camera-local space
   (above the camera), falling entirely outside the frustum.
4. is_in_camera_view returns False, the element is excluded from
   filtered_elements, and it is hidden — regardless of the fact that a
   PLAN_VIEW representation exists that would be within the frustum.

The same failure occurs in reverse: activating an RCP drawing when the
element's active mesh is the PLAN_VIEW geometry (floor level, below the
upward-looking RCP camera).

Fix

tool/drawing.py — representation-independent bbox

A new helper _get_bbox_corners(obj, element) replaces the direct use of
obj.bound_box in is_in_camera_view. It unions three bbox sources to produce
a spatial envelope that is independent of which representation is currently
active:

1. IfcBoundingBox — if the element has a Box representation context,
   the IfcBoundingBox item is read and converted to metres. This provides the
   canonical floor-plan footprint defined in the IFC file, which is always
   present regardless of which Blender mesh is active.

2. Accumulated custom properties (obj["ifc_bbox_min"] /
   obj["ifc_bbox_max"]) — a growing union of every representation bbox that
   has been loaded for this object, populated by update_bbox_accumulation (see
   below). After the first round-trip between drawing types, this covers all
   previously seen geometry extents.

3. obj.bound_box — the existing fallback for objects without IFC metadata
   or on first load.

The union of these three sources ensures the bounding envelope spans both the
floor-level footprint (for plan cameras) and the ceiling-level geometry (for
RCP cameras), so the frustum test returns True for both view types regardless
of which mesh is currently active.

is_in_camera_view gains an optional element parameter passed through from
get_elements_in_camera_view, which now iterates objects explicitly rather than
using a list comprehension so the entity lookup is available for both the test
and the result set.

tool/geometry.py — bbox accumulation

New method update_bbox_accumulation(obj) unions the current obj.bound_box
into obj["ifc_bbox_min"] / obj["ifc_bbox_max"] Blender custom properties.
The union grows monotonically as representations are loaded, so after any two
representation switches the accumulated bbox covers all seen extents.

core/geometry.py — hook into representation switching

switch_representation calls geometry.update_bbox_accumulation(obj) after
reimport_element_representations completes. This means every time a drawing
activation switches an element's mesh, the new geometry is harvested into the
accumulation automatically.

Notes

• No changes to IFC reading, writing, or any operator logic outside of the
  three files listed above.
• The IfcBoundingBox path only activates when the element has a Box
  representation context; elements without one fall through to the accumulated
  props and obj.bound_box unchanged.
• On a cold Blender session (no prior representation switches), the
  IfcBoundingBox alone is sufficient to fix the plan-view case for elements
  that carry a Box context. For elements without a Box context, the
  accumulated props will build up after the first switch.

Testing

Tested with an IFC file containing an IfcLightFixture with
Model/Body/PLAN_VIEW, Model/Body/REFLECTED_PLAN_VIEW, and
Model/Box/MODEL_VIEW representations:

• Activating the plan view drawing from a cold session (RCP mesh active):
  fixture is now included and switches to PLAN_VIEW representation. ✓
• Activating the RCP drawing after the plan view: fixture is included and
  switches to REFLECTED_PLAN_VIEW representation. ✓
• Toggling between the two drawings repeatedly: both continue to work. ✓

Generated with the assistance of an AI coding tool.