`GpencilIOParams.ob` is set to `CTX_data_active_object` at the beginning
of the export [which is not ensured to be a valid `OB_GPENCIL_LEGACY`
object, non-valid objects are filtered out later in
`create_object_list`]. From this (potential non-greasepencil) object's
data, a "global `bGPdata` is stored in `GpencilIOParams`.
From here, it can only go downwards as `stroke_point_radius_get`,
`export_stroke_to_polyline`, `BKE_gpencil_stroke_perimeter_from_view`
all use this "global" `bGPdata`.
Two possible solutions might exist:
- [1] just cancel the operator if the active object is not a
`OB_GPENCIL_LEGACY` object
- [2] make sure we use corresponding `bGPdata` when iterating over
valid objects to export
This PR chooses [2] since it also seems wrong to always use the
`bGPdata` from the active object for certain calculations when iterating
many objects. For example, the export ignores different values for
`Thickness Scale` on different objects and always takes the value from
the active object, which does not seem to be by design.
NOTE: this changes behavior (see above) but for the better
Pull Request: https://projects.blender.org/blender/blender/pulls/123224
751745b2de