fix(thickness): edit persists + wide polyline extrudes as a solid tube

Entering a thickness (DXF 39 extrusion) on a wide polyline now works end
to end:

- The properties Thickness field is a General-group common prop, so it is
  routed to apply_common_prop (set_entity_thickness) instead of the
  geometry setter, which ignored it — the value was silently dropped and
  reverted to 0.
- A wide polyline extrudes its whole band into a 3-D tube (outer + inner
  walls with top and bottom caps), not just its centreline.
- The tube is real 3-D geometry, not a flat draw-order hatch: it renders
  solid in every view mode with true depth, so nothing shows through the
  walls. The flat 2-D band fill is skipped for a thickened polyline.
- A fill whose triangles span depth keeps its real depth (no draw-order
  bias), so the extrusion's own edge wires stay in front of the surface
  and remain visible instead of only the silhouette.
- The corner and cap edge lines read black, framing the coloured tube.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update/command.rs

@@ -1576,7 +1576,13 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                                             );
                                         }
                                     }
-                                    "linetype_scale" | "transparency" => {
+                                    "linetype_scale" | "transparency" | "thickness" => {
+                                        // Thickness (DXF 39 extrusion) is a General-
+                                        // group common prop, not a geometry-group one:
+                                        // route it to apply_common_prop (which handles
+                                        // it via set_entity_thickness). apply_geom_prop
+                                        // ignores it, so the edit would otherwise be a
+                                        // silent no-op and revert to the old value.
                                         if let Some(entity) =
                                             self.tabs[i].scene.document.get_entity_mut(handle)
                                         {

src/entities/lwpolyline.rs

@@ -100,6 +100,83 @@ fn thick_segments(
     }
 }
 
+/// Extrude a *wide* LwPolyline's band into a 3-D tube: each band segment's outer
+/// and inner boundary rises by `thickness` (along the normal) into a wall,
+/// leaving the two radial segment-end edges open (they are internal to the
+/// band). The flat bottom band is already drawn by the wide-fill path; this
+/// adds the vertical walls and their outline. Used instead of `thick_segments`
+/// (which extrudes only the centreline) when the polyline carries a width.
+fn thick_wide_band(
+    pl: &LwPolyline,
+    thickness: f64,
+    to_wcs: &dyn Fn(f64, f64) -> (f64, f64, f64),
+    normal: (f64, f64, f64),
+    key_verts: Vec<[f64; 3]>,
+    tangents: Vec<TangentGeom>,
+) -> TruckEntity {
+    let (origin, fills) = wide_fills(pl);
+    let (nx, ny, nz) = normal;
+    let t = thickness;
+    let off = |p: [f64; 3]| -> [f64; 3] { [p[0] + t * nx, p[1] + t * ny, p[2] + t * nz] };
+    let push_seg = |lines: &mut Vec<[f64; 3]>, a: [f64; 3], b: [f64; 3]| {
+        lines.push(a);
+        lines.push(b);
+        lines.push([f64::NAN; 3]);
+    };
+
+    let mut lines: Vec<[f64; 3]> = Vec::new();
+    // Shaded surfaces: the vertical walls plus the top cap. The flat bottom cap
+    // is already drawn by the wide-fill hatch path, so it is not repeated here.
+    let mut fill_tris: Vec<[f64; 3]> = Vec::new();
+    for poly in &fills {
+        let n = poly.len();
+        if n < 4 {
+            continue;
+        }
+        // `polyline_segment_fill` returns the band loop as the outer boundary
+        // forward then the inner boundary back, so the two transition edges
+        // (half-1 → half and n-1 → 0) are the radial segment ends.
+        let half = n / 2;
+        let bot: Vec<[f64; 3]> = poly
+            .iter()
+            .map(|&[x, y]| {
+                let (wx, wy, wz) = to_wcs(origin[0] + x as f64, origin[1] + y as f64);
+                [wx, wy, wz]
+            })
+            .collect();
+        let top: Vec<[f64; 3]> = bot.iter().map(|&p| off(p)).collect();
+        for k in 0..n {
+            // Vertical at every boundary point.
+            push_seg(&mut lines, bot[k], top[k]);
+            // Skip the two radial cap edges — they stay inside the band.
+            if k == half - 1 || k == n - 1 {
+                continue;
+            }
+            let kn = (k + 1) % n;
+            push_seg(&mut lines, bot[k], bot[kn]); // bottom boundary
+            push_seg(&mut lines, top[k], top[kn]); // top boundary
+            // Wall quad (two triangles).
+            fill_tris.extend_from_slice(&[
+                bot[k], bot[kn], top[kn], bot[k], top[kn], top[k],
+            ]);
+        }
+        // Bottom + top caps — the band ring triangulated at each plane. The
+        // bottom cap is a real 3-D surface (with depth) so the walls occlude it
+        // correctly; the flat 2-D band fill is skipped for thickened polylines.
+        fill_tris.extend(crate::entities::mesh::triangulate_planar(&bot));
+        fill_tris.extend(crate::entities::mesh::triangulate_planar(&top));
+    }
+
+    TruckEntity {
+        pick_tris: fill_tris.clone(),
+        object: TruckObject::Lines(lines),
+        snap_pts: vec![],
+        tangent_geoms: tangents,
+        key_vertices: key_verts,
+        fill_tris,
+    }
+}
+
 fn to_truck(pline: &LwPolyline) -> TruckEntity {
     let verts = &pline.vertices;
     if verts.is_empty() {
@@ -172,6 +249,16 @@ fn to_truck(pline: &LwPolyline) -> TruckEntity {
             kv.push([wbx, wby, wbz]);
             seg_data.push((ox0, oy0, ox1, oy1));
         }
+        // A wide polyline extrudes its whole band into a tube (outer + inner
+        // walls); a zero-width one just extrudes its centreline.
+        let is_wide = pline.constant_width > 1e-9
+            || pline
+                .vertices
+                .iter()
+                .any(|v| v.start_width > 1e-9 || v.end_width > 1e-9);
+        if is_wide {
+            return thick_wide_band(pline, pline.thickness, &to_wcs, normal, kv, tgs);
+        }
         return thick_segments(&seg_data, &path, pline.thickness, normal, kv, tgs);
     }
 

src/scene/convert/tessellate.rs

@@ -1116,6 +1116,18 @@ pub fn tessellate(
                 let mut out = Vec::new();
                 let mut is_first = true;
 
+                // A thickened wide polyline's extrusion — its corner / cap edges
+                // frame the solid tube and read black (like solid-with-edges
+                // outlines), while the tube fill keeps the entity colour.
+                let edge_color = if matches!(
+                    entity,
+                    EntityType::LwPolyline(p) if p.thickness.abs() > 1e-10
+                ) {
+                    [0.0, 0.0, 0.0, 1.0]
+                } else {
+                    color
+                };
+
                 if !local_pts.is_empty() {
                     let (snap, keys, tangents) = if is_first {
                         is_first = false;
@@ -1137,7 +1149,7 @@ pub fn tessellate(
                         name: name.clone(),
                         points: local_pts,
                         points_low: local_pts_low,
-                        color,
+                        color: edge_color,
                         selected,
                         pattern_length: 0.0,
                         pattern: [0.0; 8],

src/scene/entity.rs

@@ -691,6 +691,11 @@ impl Scene {
         // Wide LWPolyline and Polyline2D fills
         for entity in self.document.entities() {
             let (common, fill_origin, fills) = match entity {
+                // A thickened wide LwPolyline becomes a 3-D tube: its bottom cap
+                // is drawn as a real depth-tested surface by the tessellator, not
+                // as this flat 2-D band (which, having only draw-order depth,
+                // would show through the tube walls in a 3-D view).
+                EntityType::LwPolyline(pl) if pl.thickness.abs() > 1e-10 => continue,
                 EntityType::LwPolyline(pl) => {
                     let (o, f) = crate::entities::lwpolyline::wide_fills(pl);
                     (&pl.common, o, f)

src/scene/pipeline/face3d_gpu.rs

@@ -211,7 +211,18 @@ impl Face3DGpu {
                 }
             } else {
                 let fill_color = [r, g, b, a];
-                let depth = depth_of(wire);
+                // A fill whose triangles span depth is a genuine 3-D surface (an
+                // extruded polyline tube), not a flat coplanar overlay (2-D SOLID,
+                // greek text, dimension background). Keep its real depth so the
+                // fill occludes correctly and its own edge wires — coincident with
+                // the surface — win the depth test and stay visible. A flat overlay
+                // keeps the draw-order bias that layers it in screen order.
+                let (mut zmin, mut zmax) = (f32::INFINITY, f32::NEG_INFINITY);
+                for p in &wire.fill_tris {
+                    zmin = zmin.min(p[2]);
+                    zmax = zmax.max(p[2]);
+                }
+                let depth = if zmax - zmin > 1e-4 { 0.0 } else { depth_of(wire) };
                 for (i, &position) in wire.fill_tris.iter().enumerate() {
                     verts_2d.push(Face3DVertex {
                         position,