Merge pull request #6716 from dotCooCoo/fix/3d-fill-walls-behind-stroke

3D: a stroke's walls cover the fill's walls at concave corners

docs/target-app-parity.md

@@ -1100,6 +1100,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - Divide uses open lines, bent paths and curves as cutting edges (#1307), preserving the frontmost filled face's appearance and holes. Engine tests cover implicit closure of filled open contours and unrelated objects; native automation confirms independent piece movement, one Undo/Redo, canvas/window captures and an exact saved-document read by a separate CLI process. The shared planar map keeps a segment cap (65,536 since #937, was 4,096) and its filled-area fallback; other Pathfinder operations are unchanged.
   - Type that Transform effects only move and copy (no scale, rotation, reflection or Random) exports as type in each place, and PDF export writes every copy as selectable, searchable text, when its characters are in solid colors without underline or strikethrough, the type object has no fills or strokes of its own, no inline graphics and no perspective, its transform does not scale or shear stroked characters, and the copies do not overlap. When the effect is on the type itself, the type can also have transparency, an opacity mask and raster effects. When the effect is on the group or layer holding the type, the type has no transparency or effects of its own and is not in a clipping path, the group or layer has no fill, stroke or Pathfinder effect of its own, and no group between them has a fill, stroke, Pathfinder or geometry effect. Type still exports as outlines when the effect stops its copies early, or when the copies would number more than 10,000 or take more than 20,000,000 bytes of document data, and so does other type under a geometry effect.
   - Extrude & Bevel and Inflate treat strokes as outlined: each visible stroke builds a solid from its outline in its own paint beside the top fill's ([three-d.md](three-d.md#fills-and-strokes)).
+  - With caps and opaque paint, Extrude & Bevel (both kinds) and Inflate draw each side face of the fill's solid before the faces of the same object's strokes that overlap it (strokes on closed paths without dashes, a width profile or a brush, in a solid color or an opaque gradient), so the stroke's walls cover the fill's walls at concave corners instead of showing stripes of the fill. Tests: `solids::tests::a_fills_walls_are_drawn_before_the_stroke_faces_over_them`, `solids::tests::the_draw_order_moves_a_fill_wall_before_the_stroke_faces_it_overlaps`, `solid::tests::facets_tell_the_sides_from_the_ends_and_the_faces_turned_away`.
   - Extrude & Bevel, Inflate and Rotate apply to type: it makes a solid of its glyph outlines, painted with its own fills and strokes or, when it has none, its characters' colour (the first run's), and stays type, so editing the text reshapes the solid (#4715).
   - Extrude & Bevel, Inflate and Rotate (Effect › 3D and Materials): live effects in the `three-d` crate with depth, twist, taper, solid or hollow caps, five original bevel shapes (width, height, repeat, spacing, inside, both sides), Inflate's volume, both sides, twist, taper and cap, Rotate's turned fills and strokes, Position presets, the rotation and light gizmos, SVG/PDF vector output and Expand Appearance; one 3D effect per object; covered by geometry, effect, canvas-versus-export, command and dialog tests ([three-d.md](three-d.md)).
   - Extrude & Bevel and Inflate build detailed shapes: each solid takes up to 65,536 outline points and 163,840 faces (VectorCraft's own limits, was 2,048 points and 32,768 faces), counted before any point is sampled; when the faces do not fit, every curve takes fewer pieces, down to 4. A closed path of 2,000 curves extrudes with a bevel and inflates, and paths of 5,000 and 10,000 curves build at the default settings (`crates/three-d/src/solid/tests_limits.rs`).

docs/three-d.md

@@ -100,7 +100,12 @@ reply on the reference app's bug forum says that strokes "will be treated as out
 The rest is our reading:
 
 - When the fill and every stroke are opaque with Normal blending, the faces of all the solids are drawn in one
-  back-to-front order, and the caps turned toward the viewer are drawn last, the lower item's first. Otherwise
+  back-to-front order, and the caps turned toward the viewer are drawn last, the lower item's first. With caps on,
+  each side face of the fill's solid that is turned toward the viewer is drawn before every face of the same
+  shape's strokes, turned toward the viewer, whose bounds overlap it, so the stroke's walls cover the fill's walls
+  at concave corners. This applies to strokes on closed paths without dashes, a width profile or a brush, painted
+  with a solid color or a gradient without transparent stops; with other strokes, and without caps, the faces keep
+  their depth order. Otherwise
   each solid is drawn on its own with its opacity and blending, the lower item's first. With a light that is not
   white, each solid is also drawn on its own when one of them is a puffed, shaded Inflate surface in a solid color
   (drawn as one composite) or is painted with a gradient that has transparent stops (drawn with an opacity mask).