feat(proxy): honour proxy-graphics colour traits

The preview stream sets a current colour (record type 14, an ACI) before
its geometry; track it and tag each decoded primitive. The Unknown-entity
path groups primitives by colour and draws one wire per colour, resolving a
real index (1..=255) to its RGB and letting ByLayer/ByBlock inherit the
entity colour. So a custom entity's preview now renders in its own colours
(e.g. an ACA door's blue swing) instead of a single flat colour.

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

src/scene/convert/proxy_graphics.rs

@@ -33,12 +33,22 @@
 /// line strips.
 pub struct ProxyPolyline {
     pub points: Vec<[f64; 3]>,
+    /// The colour in force when this primitive was emitted, as an AutoCAD
+    /// Color Index. 256 = ByLayer / 0 = ByBlock (inherit the entity's colour);
+    /// 1..=255 override it. Set from the preview's colour traits.
+    pub color: i32,
 }
 
+/// AutoCAD Color Index meaning "inherit from the layer" — the default until a
+/// colour trait says otherwise.
+const COLOR_BYLAYER: i32 = 256;
+
 const REC_ARC: u32 = 4;
 const REC_ARC5: u32 = 5;
 const REC_POLYLINE: u32 = 6;
 const REC_POLYGON: u32 = 7;
+/// Trait record that sets the current colour (ACI) for following primitives.
+const REC_COLOR: u32 = 14;
 
 fn u32_at(b: &[u8], o: usize) -> Option<u32> {
     b.get(o..o + 4).map(|s| u32::from_le_bytes([s[0], s[1], s[2], s[3]]))
@@ -74,6 +84,7 @@ pub fn decode(blob: &[u8]) -> Vec<ProxyPolyline> {
     }
 
     let mut pos = 8usize;
+    let mut color = COLOR_BYLAYER;
     for _ in 0..count {
         let Some(rsize) = u32_at(blob, pos) else { break };
         let rsize = rsize as usize;
@@ -82,6 +93,11 @@ pub fn decode(blob: &[u8]) -> Vec<ProxyPolyline> {
             break;
         }
         match rtype {
+            REC_COLOR => {
+                if let Some(c) = u32_at(blob, pos + 8) {
+                    color = c as i32;
+                }
+            }
             REC_POLYLINE | REC_POLYGON => {
                 if let Some(n) = u32_at(blob, pos + 8) {
                     let n = n as usize;
@@ -101,18 +117,18 @@ pub fn decode(blob: &[u8]) -> Vec<ProxyPolyline> {
                                     pts.push(first);
                                 }
                             }
-                            out.push(ProxyPolyline { points: pts });
+                            out.push(ProxyPolyline { points: pts, color });
                         }
                     }
                 }
             }
             REC_ARC | REC_ARC5 => {
-                if let Some(poly) = decode_arc(blob, pos) {
+                if let Some(points) = decode_arc(blob, pos) {
-                    out.push(poly);
+                    out.push(ProxyPolyline { points, color });
                 }
             }
-            // Every other record is a trait (colour, layer, lineweight, …) —
+            // Every other record is a trait (layer, lineweight, …) — skipped
-            // skipped in phase 1; `rsize` still advances us past it.
+            // for now; `rsize` still advances us past it.
             _ => {}
         }
         pos += rsize;
@@ -121,8 +137,9 @@ pub fn decode(blob: &[u8]) -> Vec<ProxyPolyline> {
 }
 
 /// Flatten a circular-arc record (centre, radius, normal, start direction,
-/// sweep) into a poly-line. The normal's Z sign gives the sweep direction.
+/// sweep) into a strip of points. The normal's Z sign gives the sweep
-fn decode_arc(blob: &[u8], pos: usize) -> Option<ProxyPolyline> {
+/// direction.
+fn decode_arc(blob: &[u8], pos: usize) -> Option<Vec<[f64; 3]>> {
     let center = pt3_at(blob, pos + 8)?;
     let radius = f64_at(blob, pos + 32)?;
     let normal = pt3_at(blob, pos + 40)?;
@@ -144,7 +161,7 @@ fn decode_arc(blob: &[u8], pos: usize) -> Option<ProxyPolyline> {
             center[2],
         ]);
     }
-    Some(ProxyPolyline { points })
+    Some(points)
 }
 
 #[cfg(test)]

src/scene/convert/tess.rs

@@ -246,22 +246,39 @@ pub(crate) fn tessellate_entity(
         if let Some(blob) = e.common().graphic_data.as_ref() {
             let polys = convert::proxy_graphics::decode(blob);
             if !polys.is_empty() {
-                // One wire for the whole preview: concatenate the poly-lines
+                // Group primitives by their preview colour so each colour draws
-                // with NaN separators (arcs are already flattened to points).
+                // in its own wire (the poly-lines within share a wire, joined by
+                // NaN separators; arcs are already flattened to points).
+                use std::collections::BTreeMap;
                 let nan = [f64::NAN; 3];
-                let mut pts64: Vec<[f64; 3]> = Vec::new();
+                let mut by_color: BTreeMap<i32, Vec<[f64; 3]>> = BTreeMap::new();
                 for poly in &polys {
-                    if !pts64.is_empty() {
+                    let buf = by_color.entry(poly.color).or_default();
-                        pts64.push(nan);
+                    if !buf.is_empty() {
+                        buf.push(nan);
                     }
-                    pts64.extend_from_slice(&poly.points);
+                    buf.extend_from_slice(&poly.points);
                 }
-                let (pts, pts_low) = convert::tessellate::points_to_ds(pts64);
+                let mut wires = Vec::with_capacity(by_color.len());
-                let mut w = WireModel::solid(h.value().to_string(), pts, entity_color, sel);
+                for (pcolor, pts64) in by_color {
-                w.points_low = pts_low;
+                    // A real ACI index overrides the entity colour; ByLayer
-                w.line_weight_px = line_weight_px;
+                    // (256) / ByBlock (0) inherit it.
-                w.aci = aci;
+                    let (col, w_aci) = if (1..=255).contains(&pcolor) {
-                return vec![w];
+                        let rgba = convert::tess_util::aci_to_rgba(
+                            &acadrust::types::Color::Index(pcolor as u8),
+                        );
+                        (view::render::adapt_to_bg(rgba, bg_color), pcolor as u8)
+                    } else {
+                        (entity_color, aci)
+                    };
+                    let (pts, pts_low) = convert::tessellate::points_to_ds(pts64);
+                    let mut w = WireModel::solid(h.value().to_string(), pts, col, sel);
+                    w.points_low = pts_low;
+                    w.line_weight_px = line_weight_px;
+                    w.aci = w_aci;
+                    wires.push(w);
+                }
+                return wires;
             }
         }
     }