Extends the curved-face wireframe treatment from cones to spheres and tori, so
a solid built from those faces reads the way a cylinder already did.
ISOLINES: sphere faces get meridian lines across the face's colatitude span at
evenly spaced longitudes; torus faces get minor cross-section circles at evenly
spaced revolution angles. Both clip to the face's own parametric window (from
the boundary polygon via a shared `angular_span` gap-finder), so a partial
sphere or torus arc doesn't draw lines out over the missing part.
Silhouettes (DISPSILH): `CurvedGen` becomes an enum. A sphere silhouettes as
the great circle perpendicular to the view, clipped to the face window; a torus
as the two curves where the tube turns edge-on, traced around the revolution.
The silhouette now uses the camera's view *direction* alone, not the eye
position — a single parallel direction for the whole scene — so the outline
follows the view angle, holds still under pan, and doesn't foreshorten, which
is the orthographic silhouette a CAD wireframe expects.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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