Extend UCS support to in-viewport (MSPACE) editing through the existing
single-converter structure: one active_ucs drives every UCS-aware system,
now in the Model tab AND inside a floating viewport.
- Single predicate DocumentTab::editing_model_space() (Model tab or active
viewport) replaces the model-only gate in ucs_wire_affine,
ucs_rotation_angle, ucs_grid_basis, viewcube_ucs_mat, the coordinate
readout and the cursor-plane pick.
- Per-viewport UCS: refresh_active_ucs() sets active_ucs to the pane's UCS
on every transition (the entered viewport's own UCS from its
ucs_origin/x_axis/y_axis/ucs_per_viewport fields, the header model UCS in
the Model tab, none in plain paper); persist_active_ucs() writes changes
back to the viewport entity or the header so they round-trip. Wired into
EnterViewport/ExitViewport, layout switch, load and the UCS command.
- Visuals: grid_views now returns each pane's handle so every content
viewport's grid aligns to its own UCS; the UCS icon draws inside the
active viewport projected through the viewport camera.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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