feat(lwpolyline): render the wide-polyline band via the wire shader

A wide polyline's flat band was drawn by the hatch pipeline: a solid fill
with only draw-order depth. It ignored the entity linetype (the width
"crushed" the dash pattern) and showed through 3-D geometry in a tilted view.

Draw the band from the polyline's own centre-line wire instead. A new
`WireModel.world_width` (drawing units) makes the wire vertex shader expand
the quad by `world_half_width / world_per_pixel` (clamped to a hairline), so
the band is sized in world units and tracks zoom. Because it is now a wire:

- the GPU dash shader dashes the band by arc-length — the linetype applies;
- it is depth-tested at the polyline elevation — no draw-order see-through;
- no CPU band triangles or per-dash geometry are generated.

`world_half_width` rides in `WireConst` (native, replacing a pad) and the web
`WireInstance` (loc 14); both wire shaders branch on it. The tessellator sets
`world_width` from the LwPolyline width on the Contour / SegmentedLines arms,
and the model-space fill loop no longer emits a hatch band for any LwPolyline.
Pick still uses the band polygon (`pick_tris`).

Blocks keep the hatch band: `LocalWire` carries no `world_width` (finalize
zeroes it), so a scaled insert still scales its band correctly.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/scene/cache/block_cache.rs

@@ -325,6 +325,12 @@ fn build_defn(
                 subs.push(LocalSub::Nested(build_nested_ref(nested_ins, doc, bg_color)));
             }
             _ => {
+                // A wide polyline inside a block keeps its thin centre-line
+                // here (`LocalWire` carries no `world_width`, and `finalize`
+                // rebuilds every block wire with `world_width: 0.0`); its band
+                // is drawn by the hatch pipeline (`push_block_wide_fills`),
+                // which transforms with the block instance so the band scales
+                // correctly. The shader band is a top-level-entity path only.
                 for lw in tessellate_sub_local(doc, entity, anno_scale, bg_color) {
                     subs.push(LocalSub::Wire(lw));
                 }
@@ -848,6 +854,7 @@ impl Batches {
                 // the cached defn.
                 let color = crate::scene::view::render::adapt_to_bg(b.color, bg_color);
                 WireModel {
+                    world_width: 0.0,
                     fill_is_3d: false,
                     pick_tris: b.pick_tris,
                     pick_tris_low: b.pick_tris_low,

src/scene/convert/tess.rs

@@ -650,6 +650,7 @@ pub(crate) fn tessellate_entity(
             (ins.insert_point.z) as f32,
         );
         let marker = WireModel {
+            world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),
@@ -1029,6 +1030,7 @@ fn lod_stub_wire(
     // LOD boundary. #19.
     let stored_color = if selected { WireModel::SELECTED } else { color };
     WireModel {
+        world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),
         pick_tris_low: Vec::new(),
@@ -1115,6 +1117,7 @@ fn lod_stub_wire_3d(
     }
     let stored_color = if selected { WireModel::SELECTED } else { color };
     WireModel {
+        world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),
         pick_tris_low: Vec::new(),

src/scene/convert/tessellate.rs

@@ -370,6 +370,7 @@ pub fn tessellate(
                     None
                 };
                 elem_wires.push(WireModel {
+                    world_width: 0.0,
                     fill_is_3d: false,
                     pick_tris: Vec::new(),
                     pick_tris_low: Vec::new(),
@@ -660,6 +661,7 @@ pub fn tessellate(
                                         ftl.push(lo);
                                     }
                                     wires.push(WireModel {
+                                        world_width: 0.0,
                                         fill_is_3d: false,
                                         pick_tris: Vec::new(),
                                         pick_tris_low: Vec::new(),
@@ -697,6 +699,7 @@ pub fn tessellate(
                                         fpl.push(lo);
                                     }
                                     wires.push(WireModel {
+                                        world_width: 0.0,
                                         fill_is_3d: false,
                                         pick_tris: Vec::new(),
                                         pick_tris_low: Vec::new(),
@@ -741,6 +744,7 @@ pub fn tessellate(
                             low.push(ll);
                         }
                         wires.push(WireModel {
+                            world_width: 0.0,
                             fill_is_3d: false,
                             pick_tris: Vec::new(),
                             pick_tris_low: Vec::new(),
@@ -766,6 +770,7 @@ pub fn tessellate(
                         });
                     }
                     wires.push(WireModel {
+                        world_width: 0.0,
                         fill_is_3d: false,
                         pick_tris: Vec::new(),
                         pick_tris_low: Vec::new(),
@@ -821,6 +826,7 @@ pub fn tessellate(
                             (Vec::new(), Vec::new(), Vec::new())
                         };
                         out.push(WireModel {
+                            world_width: 0.0,
                             fill_is_3d: false,
                             pick_tris: Vec::new(),
                             pick_tris_low: Vec::new(),
@@ -858,6 +864,7 @@ pub fn tessellate(
                             (Vec::new(), Vec::new(), Vec::new())
                         };
                         out.push(WireModel {
+                            world_width: 0.0,
                             fill_is_3d: false,
                             pick_tris: Vec::new(),
                             pick_tris_low: Vec::new(),
@@ -892,6 +899,7 @@ pub fn tessellate(
                 // are empty → the early-return path above).
                 if !sdf_verts.is_empty() {
                     out.push(WireModel {
+                        world_width: 0.0,
                         fill_is_3d: false,
                         pick_tris: Vec::new(),
                         pick_tris_low: Vec::new(),
@@ -919,6 +927,7 @@ pub fn tessellate(
 
                 if out.is_empty() {
                     out.push(WireModel {
+                        world_width: 0.0,
                         fill_is_3d: false,
                         pick_tris: Vec::new(),
                         pick_tris_low: Vec::new(),
@@ -968,6 +977,7 @@ pub fn tessellate(
                             .map(|[kx, ky, kz]| [kx, ky, kz])
                             .collect();
                         return vec![WireModel {
+                            world_width: 0.0,
                             fill_is_3d: false,
                             pick_tris: Vec::new(),
                             pick_tris_low: Vec::new(),
@@ -1016,6 +1026,7 @@ pub fn tessellate(
                         .map(|[x, y, z]| [x, y, z])
                         .collect();
                     return vec![WireModel {
+                        world_width: 0.0,
                         fill_is_3d: false,
                         pick_tris: Vec::new(),
                         pick_tris_low: Vec::new(),
@@ -1052,9 +1063,12 @@ pub fn tessellate(
                         .into_iter()
                         .map(|[x, y, z]| [x, y, z])
                         .collect();
-                    // A wide polyline arrives here: its band is pick geometry.
+                    // A wide polyline arrives here: the shader expands this
+                    // centre-line to `world_width` so the band IS the wire (the
+                    // linetype dashes it); the band also backs pick.
                     let (pick_tris, pick_tris_low) = points_to_ds(te.pick_tris);
                     return vec![WireModel {
+                        world_width: lwpolyline_band_width(entity),
                         fill_is_3d: false,
                         pick_tris,
                         pick_tris_low,
@@ -1140,6 +1154,7 @@ pub fn tessellate(
                         (Vec::new(), Vec::new(), Vec::new())
                     };
                     out.push(WireModel {
+                        world_width: 0.0,
                         fill_is_3d: false,
                         pick_tris,
                         pick_tris_low,
@@ -1176,6 +1191,7 @@ pub fn tessellate(
                         (Vec::new(), Vec::new(), Vec::new())
                     };
                     out.push(WireModel {
+                        world_width: 0.0,
                         pick_tris: Vec::new(),
                         pick_tris_low: Vec::new(),
             dash_from_start: false,
@@ -1203,6 +1219,7 @@ pub fn tessellate(
 
                 if out.is_empty() {
                     out.push(WireModel {
+                        world_width: 0.0,
                         fill_is_3d: false,
                         pick_tris: Vec::new(),
                         pick_tris_low: Vec::new(),
@@ -1239,9 +1256,11 @@ pub fn tessellate(
                     .into_iter()
                     .map(|[x, y, z]| [x, y, z])
                     .collect();
-                // A wide polyline with PLINEGEN=0 arrives here.
+                // A wide polyline with PLINEGEN=0 arrives here: same shader-band
+                // treatment as the Contour arm, restarting the dash per segment.
                 let (pick_tris, pick_tris_low) = points_to_ds(te.pick_tris);
                 return vec![WireModel {
+                    world_width: lwpolyline_band_width(entity),
                     fill_is_3d: false,
                     pick_tris,
                     pick_tris_low,
@@ -1310,6 +1329,7 @@ pub fn tessellate(
     let snap_pts: Vec<(glam::DVec3, SnapHint)> =
         snap_pts.into_iter().map(|(p, h)| (p.as_dvec3(), h)).collect();
     vec![WireModel {
+        world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),
         pick_tris_low: Vec::new(),
@@ -1489,6 +1509,29 @@ pub(crate) fn entity_z(entity: &EntityType) -> f32 {
     }
 }
 
+/// Band width (drawing units) of a wide LwPolyline whose flat band is drawn by
+/// expanding its centre-line wire in the shader. `0.0` = a zero-width polyline
+/// or a non-LwPolyline (a normal screen-pixel wire). A thickness-extruded
+/// polyline is excluded: its band becomes a 3-D tube (`thick_wide_band`), not a
+/// flat shader band. A tapering polyline (per-vertex start/end widths) collapses
+/// to its widest edge — the shader carries one width per wire.
+fn lwpolyline_band_width(entity: &EntityType) -> f32 {
+    match entity {
+        EntityType::LwPolyline(p) if p.thickness.abs() <= 1e-10 => {
+            let mut w = p.constant_width;
+            for v in &p.vertices {
+                w = w.max(v.start_width).max(v.end_width);
+            }
+            if w > 1e-9 {
+                w as f32
+            } else {
+                0.0
+            }
+        }
+        _ => 0.0,
+    }
+}
+
 // ── Fallback geometry (Viewport, Insert, Hatch outline, Ole2Frame) ───────
 //
 // Per-entity blocks have moved to their respective `entities/*.rs` files

src/scene/entity.rs

@@ -691,15 +691,14 @@ 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)
-                }
+                // A wide LwPolyline no longer draws its band here: the shader
+                // expands the centre-line wire to `world_width` (a real
+                // depth-tested band that also carries the linetype dash), so a
+                // second flat 2-D band with only draw-order depth would double
+                // it and show through 3-D geometry. A thickened one is likewise
+                // a 3-D tube built by the tessellator. Its band still backs pick
+                // (`pick_tris`), just not this fill.
+                EntityType::LwPolyline(_) => continue,
                 EntityType::Polyline2D(pl) => {
                     let (o, f) = crate::entities::polyline::wide_fills(pl);
                     (&pl.common, o, f)

src/scene/model/wire_model.rs

@@ -54,6 +54,12 @@ pub struct WireModel {
     pub pattern: [f32; 8],
     /// Rendered line width in screen pixels (half-width = line_weight_px / 2).
     pub line_weight_px: f32,
+    /// World-space band width (drawing units). `0.0` = a normal wire whose
+    /// width comes from `line_weight_px` (screen pixels). Non-zero = a wide
+    /// polyline: the shader expands this centre-line to `world_width` world
+    /// units (scaling with zoom) so the band IS the wire — the linetype dash
+    /// pattern then applies to the band instead of a separate hatch fill.
+    pub world_width: f32,
     /// ACI color index (1-255).  0 means true-color or unknown (no CTB lookup).
     pub aci: u8,
     /// Pre-baked snap candidates (Center, Node, Quadrant, Insertion).
@@ -173,6 +179,7 @@ impl WireModel {
     /// Create a solid wire (no dash pattern, 1px weight).
     pub fn solid(name: String, points: Vec<[f32; 3]>, color: [f32; 4], selected: bool) -> Self {
         Self {
+            world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),
@@ -394,6 +401,7 @@ impl Default for WireModel {
             pattern_length: 0.0,
             pattern: [0.0; 8],
             line_weight_px: 1.0,
+            world_width: 0.0,
             aci: 0,
             snap_pts: Vec::new(),
             tangent_geoms: Vec::new(),

src/scene/pipeline/wire_gpu.rs

@@ -119,7 +119,11 @@ pub struct WireConst {
     pub draw_depth: f32,
     pub align_end: f32,
     pub align_total: f32,
-    pub _pad0: f32,
+    /// World-space half-width for a wide-polyline band. `0.0` = a normal wire
+    /// (uses `half_width`, screen pixels). Non-zero = the vertex shader expands
+    /// the quad by `world_half_width / world_per_pixel` so the band tracks zoom
+    /// in drawing units.
+    pub world_half_width: f32,
     pub _pad1: f32,
     pub _pad2: f32,
 }
@@ -171,6 +175,9 @@ pub struct WireInstance {
     /// and the total wire length. `align_total == 0.0` = not aligned.
     pub align_end: f32,
     pub align_total: f32,
+    /// World-space half-width for a wide-polyline band (see `WireConst`). `0.0`
+    /// = a normal wire (uses `half_width`, screen pixels).
+    pub world_half_width: f32,
 }
 
 #[cfg(target_arch = "wasm32")]
@@ -194,6 +201,7 @@ impl WireInstance {
             wgpu::VertexAttribute { offset: std::mem::offset_of!(WireInstance, pos_b_low) as u64,      shader_location: 11, format: wgpu::VertexFormat::Float32x3 },
             wgpu::VertexAttribute { offset: std::mem::offset_of!(WireInstance, align_end) as u64,      shader_location: 12, format: wgpu::VertexFormat::Float32   },
             wgpu::VertexAttribute { offset: std::mem::offset_of!(WireInstance, align_total) as u64,    shader_location: 13, format: wgpu::VertexFormat::Float32   },
+            wgpu::VertexAttribute { offset: std::mem::offset_of!(WireInstance, world_half_width) as u64, shader_location: 14, format: wgpu::VertexFormat::Float32 },
         ];
         wgpu::VertexBufferLayout {
             array_stride: std::mem::size_of::<WireInstance>() as u64,
@@ -403,6 +411,7 @@ fn emit_wire_instances(wire: &WireModel, color: [f32; 4], draw_depth: f32) -> Ve
             draw_depth,
             align_end,
             align_total,
+            world_half_width: wire.world_width * 0.5,
         });
     }
     instances
@@ -427,7 +436,7 @@ pub(crate) fn emit_wire_native(
         draw_depth,
         align_end,
         align_total,
-        _pad0: 0.0,
+        world_half_width: wire.world_width * 0.5,
         _pad1: 0.0,
         _pad2: 0.0,
     };

src/scene/text/complex_lt.rs

@@ -305,6 +305,7 @@ pub fn apply_along(
         .into_iter()
         .filter(|s| s.len() >= 2)
         .map(|pts| WireModel {
+            world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),
@@ -344,6 +345,7 @@ pub fn apply_along(
             xy = xy.max(y);
         }
         out.push(WireModel {
+            world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),