fix(blocks): layer-0 children inherit the block instance layer (#221)

Entities inside a block definition that sit on layer "0" must take on the
properties of the layer the block reference is inserted on; every other
layer is "sticky" and keeps its own identity. OpenCADStudio resolved a
block child's ByLayer color/linetype/lineweight against the child's own
layer in all cases, so layer-0 content stayed layer-0 (white) instead of
inheriting the instance layer.

Resolution now follows the standard rule for block children — explicit
wins, then ByBlock → the insert's own style, then layer-0 + ByLayer →
the insert's *layer* style, else the child's own layer. The insert's
layer style threads through the whole block-expansion chain (and chains
correctly through nested inserts), with the child's own transparency
preserved.

Covered across every block-render path:
- wires (line/arc/circle/polyline/text) via the block cache + the
  explode fallback + insert attributes
- hatch / solid fills (also fixes the PDF/print export path)
- 3D solid block children (per-instance mesh recolor)
- Dimension / Table baked-block sub-entities

New shared helpers in scene::view::render: InheritStyle, layer_render_style,
lineweight_to_px; render_style_for_block_sub gained the layer-0 branch.
Adds unit tests covering the layer-0, sticky-layer, ByBlock, explicit and
transparency cases.

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

src/entities/insert.rs

@@ -133,6 +133,7 @@ pub(crate) fn append_insert_attribute_wires(
     ins_pat_len: f32,
     ins_pat: [f32; 8],
     ins_lw_px: f32,
+    ins_layer: render::InheritStyle,
     bg_color: [f32; 4],
     is_xref: bool,
     pslt_factor: f32,
@@ -162,6 +163,7 @@ pub(crate) fn append_insert_attribute_wires(
             ins_pat_len,
             ins_pat,
             ins_lw_px,
+            ins_layer,
         );
         let sub_color = render::adapt_to_bg(sub_color, bg_color);
         let sub_color = if is_xref && !sel {

src/scene/cache/block_cache.rs

@@ -59,6 +59,13 @@ pub struct LocalWire {
     pub color_is_byblock: bool,
     pub lt_is_byblock: bool,
     pub lw_is_byblock: bool,
+    /// Set when this child sits on layer "0" and the matching property is
+    /// ByLayer. At expand time the value is then taken from the INSERT's
+    /// *layer* (the layer-0 inheritance rule) instead of the cached layer-0
+    /// value baked here.
+    pub color_l0: bool,
+    pub lt_l0: bool,
+    pub lw_l0: bool,
     /// XY bounding box of this wire in block-local coordinates.
     /// `[min_x, min_y, max_x, max_y]`. Used for view-frustum culling at
     /// expand-time: transform corners by the Insert transform → world AABB
@@ -89,6 +96,18 @@ pub struct NestedRef {
     pub color_is_byblock: bool,
     pub lt_is_byblock: bool,
     pub lw_is_byblock: bool,
+    /// The nested INSERT's own properties are ByLayer. Combined with
+    /// `layer_is_zero` these drive the layer-0 rule for the nested insert
+    /// *itself* (so its ByBlock leaves inherit the outer layer, not layer 0).
+    pub color_is_bylayer: bool,
+    pub lt_is_bylayer: bool,
+    pub lw_is_bylayer: bool,
+    /// The nested INSERT itself sits on layer "0": its own layer-0 children
+    /// chain up to the outer insert's layer rather than resolving to `l0`.
+    pub layer_is_zero: bool,
+    /// The nested INSERT's own layer style — the layer-0 inheritance target
+    /// for its children when the nested insert is not itself on layer 0.
+    pub l0: crate::scene::view::render::InheritStyle,
     pub instance_offsets: Vec<[f64; 3]>,
     /// XCLIP boundary for this nested insert, in the parent defn's local frame
     /// (`None` = unclipped). Baked at build time because the clip's spatial
@@ -322,6 +341,9 @@ fn build_nested_ref(
     // against different backgrounds without rebuilding.
     let (ins_color, ins_pat_len, ins_pat, ins_lw_px, _) =
         crate::scene::view::render::render_style_for(doc, &EntityType::Insert(nested_ins.clone()));
+    // The nested insert's own layer style — the layer-0 target for its
+    // children (raw colour; adapted at emit like `ins_color`).
+    let l0 = crate::scene::view::render::layer_render_style(doc, &nested_ins.common.layer);
     let _ = bg_color;
 
     // Bake the XCLIP boundary (parent-defn-local) so the nested insert keeps
@@ -340,6 +362,17 @@ fn build_nested_ref(
         color_is_byblock: nested_ins.common.color == AcadColor::ByBlock,
         lt_is_byblock: nested_ins.common.linetype.eq_ignore_ascii_case("byblock"),
         lw_is_byblock: matches!(nested_ins.common.line_weight, LineWeight::ByBlock),
+        color_is_bylayer: nested_ins.common.color == AcadColor::ByLayer,
+        lt_is_bylayer: {
+            let lt = &nested_ins.common.linetype;
+            lt.is_empty() || lt.eq_ignore_ascii_case("bylayer")
+        },
+        lw_is_bylayer: matches!(
+            nested_ins.common.line_weight,
+            LineWeight::ByLayer | LineWeight::Default
+        ),
+        layer_is_zero: nested_ins.common.layer == "0",
+        l0,
         instance_offsets: array_offsets(nested_ins),
         clip_poly,
     }
@@ -372,6 +405,21 @@ fn tessellate_sub_local(
     let lt_is_byblock = sub.common().linetype.eq_ignore_ascii_case("byblock");
     let lw_is_byblock = matches!(sub.common().line_weight, LineWeight::ByBlock);
 
+    // Layer-0 rule: a child on layer "0" with ByLayer properties inherits the
+    // INSERT's layer at expand time. Flag each ByLayer property so emit_wire
+    // can override the cached (layer-0-resolved) value with the insert layer's.
+    let on_l0 = sub.common().layer == "0";
+    let color_l0 = on_l0 && sub.common().color == AcadColor::ByLayer;
+    let lt_l0 = on_l0 && {
+        let lt = &sub.common().linetype;
+        lt.is_empty() || lt.eq_ignore_ascii_case("bylayer")
+    };
+    let lw_l0 = on_l0
+        && matches!(
+            sub.common().line_weight,
+            LineWeight::ByLayer | LineWeight::Default
+        );
+
     // Pass `local_offset` as the f64 world-offset so tessellate subtracts it
     // before casting to f32 — same precision-preservation trick used for
     // top-level entities, applied per-defn.
@@ -437,6 +485,9 @@ fn tessellate_sub_local(
             color_is_byblock,
             lt_is_byblock,
             lw_is_byblock,
+            color_l0,
+            lt_l0,
+            lw_l0,
             aabb_local,
             text_height_local,
             text_obb_local,
@@ -537,6 +588,8 @@ pub fn expand_insert(
     ins_pat_len: f32,
     ins_pat: [f32; 8],
     ins_lw_px: f32,
+    // The INSERT's own layer style — layer-0 inheritance target for children.
+    ins_layer: crate::scene::view::render::InheritStyle,
     selected: bool,
     pslt_factor: f32,
     // World-space XY view AABB (with world_offset already subtracted, so the
@@ -598,6 +651,7 @@ pub fn expand_insert(
             ins_pat_len,
             ins_pat,
             ins_lw_px,
+            l0: ins_layer,
             selected,
             pslt_factor,
             view_aabb,
@@ -693,18 +747,7 @@ fn emit_greeked_text(
         return;
     }
 
-    let final_color = if ctx.selected {
-        WireModel::SELECTED
-    } else if lw.color_is_byblock {
-        ctx.ins_color
-    } else {
-        lw.color
-    };
-    let final_color = if ctx.is_xref && !ctx.selected {
-        fade_toward_bg(final_color, ctx.bg_color)
-    } else {
-        final_color
-    };
+    let final_color = resolve_wire_color(lw, ctx);
 
     let key = style_key(final_color, 0.0, [0.0; 8], 1.0, lw.aci, true, true);
     let entry = out
@@ -790,18 +833,7 @@ fn emit_text_baseline(
         (ux / ulen, uy / ulen, uz / ulen)
     };
 
-    let final_color = if ctx.selected {
-        WireModel::SELECTED
-    } else if lw.color_is_byblock {
-        ctx.ins_color
-    } else {
-        lw.color
-    };
-    let final_color = if ctx.is_xref && !ctx.selected {
-        fade_toward_bg(final_color, ctx.bg_color)
-    } else {
-        final_color
-    };
+    let final_color = resolve_wire_color(lw, ctx);
 
     let key = style_key(final_color, 0.0, [0.0; 8], 1.0, lw.aci, true, false);
     let entry = out
@@ -868,6 +900,9 @@ struct ExpandCtx<'a> {
     ins_pat_len: f32,
     ins_pat: [f32; 8],
     ins_lw_px: f32,
+    /// Layer-0 inheritance target — the current INSERT's *layer* style, used
+    /// for child wires on layer "0" whose properties are ByLayer.
+    l0: crate::scene::view::render::InheritStyle,
     selected: bool,
     pslt_factor: f32,
     // World-space XY view AABB (post world_offset). `None` = no culling.
@@ -1202,28 +1237,43 @@ fn expand_defn(
                         continue;
                     }
                 }
-                // Resolve ByBlock for this nested ref against the outer ctx.
+                // Resolve the nested insert's own style against the outer ctx:
+                // ByBlock inherits the outer insert; a nested insert that is
+                // itself on layer "0" with ByLayer props inherits the outer
+                // layer-0 target (so its ByBlock leaves resolve to that layer,
+                // not layer 0). Mirrors the leaf resolution in emit_wire.
                 let nested_color = if nref.color_is_byblock {
                     ctx.ins_color
+                } else if nref.layer_is_zero && nref.color_is_bylayer {
+                    ctx.l0.color
                 } else {
                     nref.ins_color
                 };
                 let (nested_pat_len, nested_pat) = if nref.lt_is_byblock {
                     (ctx.ins_pat_len, ctx.ins_pat)
+                } else if nref.layer_is_zero && nref.lt_is_bylayer {
+                    (ctx.l0.pat_len, ctx.l0.pat)
                 } else {
                     (nref.ins_pat_len, nref.ins_pat)
                 };
                 let nested_lw_px = if nref.lw_is_byblock {
                     ctx.ins_lw_px
+                } else if nref.layer_is_zero && nref.lw_is_bylayer {
+                    ctx.l0.lw_px
                 } else {
                     nref.ins_lw_px
                 };
+                // Layer-0 target for the nested expansion: a nested insert that
+                // is itself on layer 0 chains up to the outer target; otherwise
+                // its layer-0 children resolve to the nested insert's own layer.
+                let nested_l0 = if nref.layer_is_zero { ctx.l0 } else { nref.l0 };
                 let inner_ctx = ExpandCtx {
                     cache: ctx.cache,
                     ins_color: nested_color,
                     ins_pat_len: nested_pat_len,
                     ins_pat: nested_pat,
                     ins_lw_px: nested_lw_px,
+                    l0: nested_l0,
                     selected: ctx.selected,
                     pslt_factor: ctx.pslt_factor,
                     view_aabb: ctx.view_aabb,
@@ -1279,6 +1329,28 @@ fn expand_defn(
     }
 }
 
+/// Resolve a cached LocalWire's final colour against the current expansion
+/// context: selection override first, then ByBlock → insert colour, then the
+/// layer-0 rule → insert-layer colour, else the cached colour; finally xref
+/// fade. Shared by the stroke, fill, and greeked-text emit paths.
+fn resolve_wire_color(lw: &LocalWire, ctx: &ExpandCtx) -> [f32; 4] {
+    let c = if ctx.selected {
+        WireModel::SELECTED
+    } else if lw.color_is_byblock {
+        ctx.ins_color
+    } else if lw.color_l0 {
+        // Inherit the insert layer's RGB but keep the child's own transparency.
+        [ctx.l0.color[0], ctx.l0.color[1], ctx.l0.color[2], lw.color[3]]
+    } else {
+        lw.color
+    };
+    if ctx.is_xref && !ctx.selected {
+        fade_toward_bg(c, ctx.bg_color)
+    } else {
+        c
+    }
+}
+
 fn emit_wire(
     lw: &LocalWire,
     accum_xform: &Transform,
@@ -1291,25 +1363,18 @@ fn emit_wire(
 
     // Resolve final style for this LocalWire against the outer Insert ctx
     // before we hash it into a batch.
-    let final_color = if ctx.selected {
-        WireModel::SELECTED
-    } else if lw.color_is_byblock {
-        ctx.ins_color
-    } else {
-        lw.color
-    };
-    let final_color = if ctx.is_xref && !ctx.selected {
-        fade_toward_bg(final_color, ctx.bg_color)
-    } else {
-        final_color
-    };
+    let final_color = resolve_wire_color(lw, ctx);
     let (final_pat_len, final_pat) = if lw.lt_is_byblock {
         (ctx.ins_pat_len, ctx.ins_pat)
+    } else if lw.lt_l0 {
+        (ctx.l0.pat_len, ctx.l0.pat)
     } else {
         (lw.pattern_length, lw.pattern)
     };
     let final_lw_px = if lw.lw_is_byblock {
         ctx.ins_lw_px
+    } else if lw.lw_l0 {
+        ctx.l0.lw_px
     } else {
         lw.line_weight_px
     };

src/scene/convert/tess.rs

@@ -220,6 +220,20 @@ pub(crate) fn tessellate_entity(
                 if !br.entity_handles.is_empty() {
                     let mut wires: Vec<WireModel> =
                         Vec::with_capacity(br.entity_handles.len());
+                    // The Dimension's own layer style — layer-0 inheritance
+                    // target for baked sub-entities on layer "0" (#221).
+                    let dim_l0_color = view::render::adapt_to_bg(
+                        view::render::layer_render_style(document, &e.common().layer).color,
+                        bg_color,
+                    );
+                    let dim_l0_aci = document
+                        .layers
+                        .get(&e.common().layer)
+                        .map(|l| match &l.color {
+                            acadrust::types::Color::Index(i) => *i,
+                            _ => 0,
+                        })
+                        .unwrap_or(0);
                     for &eh in &br.entity_handles {
                         let Some(sub) = document.get_entity(eh) else { continue };
                         // Sub-entities inside *D### / DIMBLOCK## blocks
@@ -227,6 +241,8 @@ pub(crate) fn tessellate_entity(
                         // they should inherit from the Dimension entity.
                         let sub_color_is_byblock =
                             sub.common().color == acadrust::types::Color::ByBlock;
+                        let sub_is_l0_bylayer = sub.common().layer == "0"
+                            && sub.common().color == acadrust::types::Color::ByLayer;
                         let sub_wires = tessellate_entity(
                             document, selected, active_viewport, bg_color,
                             // Block contents are baked at the final WCS size —
@@ -238,10 +254,14 @@ pub(crate) fn tessellate_entity(
                             // Override ByBlock colour with the dim's resolved
                             // colour so text matches `DIMCLRT`-style behaviour
                             // (or layer colour) instead of the raw ByBlock
-                            // fallback that render_style_for produces.
+                            // fallback that render_style_for produces. A layer-0
+                            // sub inherits the dim's layer colour instead.
                             if sub_color_is_byblock {
                                 w.color = if sel { WireModel::SELECTED } else { entity_color };
                                 w.aci = aci;
+                            } else if sub_is_l0_bylayer && !sel {
+                                w.color = dim_l0_color;
+                                w.aci = dim_l0_aci;
                             }
                             wires.push(w);
                         }
@@ -320,10 +340,26 @@ pub(crate) fn tessellate_entity(
                 if !br.entity_handles.is_empty() {
                     let mut wires: Vec<WireModel> =
                         Vec::with_capacity(br.entity_handles.len());
+                    // The Table's own layer style — layer-0 inheritance target
+                    // for baked sub-entities on layer "0" (#221).
+                    let tab_l0_color = view::render::adapt_to_bg(
+                        view::render::layer_render_style(document, &e.common().layer).color,
+                        bg_color,
+                    );
+                    let tab_l0_aci = document
+                        .layers
+                        .get(&e.common().layer)
+                        .map(|l| match &l.color {
+                            acadrust::types::Color::Index(i) => *i,
+                            _ => 0,
+                        })
+                        .unwrap_or(0);
                     for &eh in &br.entity_handles {
                         let Some(sub) = document.get_entity(eh) else { continue };
                         let sub_color_is_byblock =
                             sub.common().color == acadrust::types::Color::ByBlock;
+                        let sub_is_l0_bylayer = sub.common().layer == "0"
+                            && sub.common().color == acadrust::types::Color::ByLayer;
                         let sub_wires = tessellate_entity(
                             document, selected, active_viewport, bg_color,
                             anno_scale, sub, block_cache, view_aabb, world_per_pixel,
@@ -333,6 +369,9 @@ pub(crate) fn tessellate_entity(
                             if sub_color_is_byblock {
                                 w.color = if sel { WireModel::SELECTED } else { entity_color };
                                 w.aci = aci;
+                            } else if sub_is_l0_bylayer && !sel {
+                                w.color = tab_l0_color;
+                                w.aci = tab_l0_aci;
                             }
                             wires.push(w);
                         }
@@ -367,6 +406,13 @@ pub(crate) fn tessellate_entity(
         // Resolve the INSERT's own style so ByBlock sub-entities can inherit it.
         let (ins_color, ins_pat_len, ins_pat, ins_lw_px, _) = view::render::render_style_for(document, e);
         let ins_color = view::render::adapt_to_bg(ins_color, bg_color);
+        // Resolve the INSERT's *layer* style — the layer-0 inheritance target
+        // for sub-entities on layer "0" with ByLayer properties (#221).
+        let ins_layer = {
+            let mut s = view::render::layer_render_style(document, &ins.common.layer);
+            s.color = view::render::adapt_to_bg(s.color, bg_color);
+            s
+        };
         let ip = glam::Vec3::new(
             (ins.insert_point.x) as f32,
             (ins.insert_point.y) as f32,
@@ -408,6 +454,7 @@ pub(crate) fn tessellate_entity(
                 ins_pat_len,
                 ins_pat,
                 ins_lw_px,
+                ins_layer,
                 sel,
                 pslt_factor,
                 view_aabb,
@@ -438,6 +485,7 @@ pub(crate) fn tessellate_entity(
                     ins_pat_len,
                     ins_pat,
                     ins_lw_px,
+                    ins_layer,
                     bg_color,
                     is_xref,
                     pslt_factor,
@@ -469,6 +517,7 @@ pub(crate) fn tessellate_entity(
                         ins_pat_len,
                         ins_pat,
                         ins_lw_px,
+                        ins_layer,
                     );
                 let sub_color = view::render::adapt_to_bg(sub_color, bg_color);
                 let sub_color = if is_xref && !sel {
@@ -509,6 +558,7 @@ pub(crate) fn tessellate_entity(
             ins_pat_len,
             ins_pat,
             ins_lw_px,
+            ins_layer,
             bg_color,
             is_xref,
             pslt_factor,

src/scene/entity.rs

@@ -377,6 +377,12 @@ impl Scene {
             })
             .collect();
 
+        // Background for adapting block-child hatch colours at the leaf (#221).
+        let hatch_bg: [f32; 4] = if self.current_layout != "Model" {
+            self.paper_bg_color
+        } else {
+            self.bg_color
+        };
         for entity in self.document.entities() {
             let EntityType::Insert(ins) = entity else {
                 continue;
@@ -402,26 +408,81 @@ impl Scene {
             // hatches land in the correct world position. A depth guard keeps
             // a malformed cyclic block reference from looping forever.
             let normalize = crate::modules::draw::modify::explode::normalize_insert_entity;
-            let mut stack: Vec<(EntityType, usize)> = ins
+            // Block-child colour inheritance sources (#221), kept RAW and
+            // adapted at the leaf. `ins_color` feeds ByBlock; `l0` (the
+            // INSERT's *layer* style) feeds the layer-0 rule. Both chain
+            // through nested inserts, mirroring expand_insert.
+            let ins_color =
+                crate::scene::view::render::render_style_for(&self.document, entity).0;
+            let l0 = crate::scene::view::render::layer_render_style(
+                &self.document,
+                &ins.common.layer,
+            );
+            let mut stack: Vec<(
+                EntityType,
+                usize,
+                [f32; 4],
+                crate::scene::view::render::InheritStyle,
+            )> = ins
                 .explode_from_document(&self.document)
                 .into_iter()
-                .map(|e| (normalize(e), 0usize))
+                .map(|e| (normalize(e), 0usize, ins_color, l0))
                 .collect();
-            while let Some((sub, depth)) = stack.pop() {
+            while let Some((sub, depth, sub_ins_color, sub_l0)) = stack.pop() {
                 match sub {
                     EntityType::Insert(nins) => {
                         if depth >= 32 {
                             continue;
                         }
+                        use acadrust::types::Color;
+                        // Chain the inheritance sources into the nested insert,
+                        // mirroring expand_insert's nested resolution: ByBlock →
+                        // parent source; layer-0 + ByLayer → parent layer-0
+                        // target; else the nested insert's own resolved style.
+                        let child_ins_color = if nins.common.color == Color::ByBlock {
+                            sub_ins_color
+                        } else if nins.common.layer == "0"
+                            && nins.common.color == Color::ByLayer
+                        {
+                            sub_l0.color
+                        } else {
+                            crate::scene::view::render::render_style_for(
+                                &self.document,
+                                &EntityType::Insert(nins.clone()),
+                            )
+                            .0
+                        };
+                        let child_l0 = if nins.common.layer == "0" {
+                            sub_l0
+                        } else {
+                            crate::scene::view::render::layer_render_style(
+                                &self.document,
+                                &nins.common.layer,
+                            )
+                        };
                         for e in nins.explode_from_document(&self.document) {
-                            stack.push((normalize(e), depth + 1));
+                            stack.push((normalize(e), depth + 1, child_ins_color, child_l0));
                         }
                     }
                     EntityType::Hatch(dxf) => {
                         if dxf.common.invisible || layer_hidden(&dxf.common.layer) {
                             continue;
                         }
-                        let color = self.render_style(&EntityType::Hatch(dxf.clone())).0;
+                        // Resolve ByBlock / layer-0 inheritance for this block
+                        // child, then adapt to the background (#221). Pattern /
+                        // lineweight args are unused by a hatch's colour.
+                        let color = crate::scene::view::render::render_style_for_block_sub(
+                            &self.document,
+                            &EntityType::Hatch(dxf.clone()),
+                            sub_ins_color,
+                            0.0,
+                            [0.0; 8],
+                            0.0,
+                            sub_l0,
+                        )
+                        .0;
+                        let color =
+                            crate::scene::view::render::adapt_to_bg(color, hatch_bg);
                         if let Some(mut model) =
                             Self::hatch_model_from_dxf(&dxf, color)
                         {

src/scene/mod.rs

@@ -2321,8 +2321,28 @@ impl Scene {
                 if !self.mesh_entity_visible(ins.common.handle) {
                     continue;
                 }
+                // Colour inheritance sources for block-internal solids (#221).
+                let bg = self.current_bg();
+                let ins_color = crate::scene::view::render::adapt_to_bg(
+                    crate::scene::view::render::render_style_for(&self.document, e).0,
+                    bg,
+                );
+                let l0 = crate::scene::view::render::adapt_to_bg(
+                    crate::scene::view::render::layer_render_style(
+                        &self.document,
+                        &ins.common.layer,
+                    )
+                    .color,
+                    bg,
+                );
                 let start = out.len();
-                self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, &mut out);
+                self.expand_block_meshes(
+                    &ins.block_name,
+                    &ins.get_transform(),
+                    0,
+                    Some((ins_color, l0)),
+                    &mut out,
+                );
                 // Tag the instanced meshes with the parent INSERT handle so the
                 // hover / selection highlight (keyed on the mesh name) tints the
                 // block, not the inner solid's own handle which nothing selects.
@@ -2344,6 +2364,11 @@ impl Scene {
         block_name: &str,
         accum: &acadrust::types::Transform,
         depth: usize,
+        // Block-child colour inheritance sources, bg-adapted:
+        // `(insert_color, insert_layer_color)`. `Some` only on the render path;
+        // pick paths pass `None` (colour irrelevant). Drives the ByBlock /
+        // layer-0 overrides for block-internal solids (#221).
+        inherit: Option<([f32; 4], [f32; 4])>,
         out: &mut Vec<MeshLodSet>,
     ) {
         if depth > 16 {
@@ -2364,13 +2389,103 @@ impl Scene {
             }
             if let EntityType::Insert(ins) = e {
                 let composed = ins.get_transform().then(accum);
-                self.expand_block_meshes(&ins.block_name, &composed, depth + 1, out);
+                let child = inherit.map(|(pc, pl0)| self.chain_mesh_inherit(ins, pc, pl0));
+                self.expand_block_meshes(&ins.block_name, &composed, depth + 1, child, out);
             } else if let Some(set) = self.block_meshes.get(&h) {
-                out.push(transform_block_mesh_lod_set(set, accum));
+                // The solid's own transparency (baked into the cached colour).
+                let own_alpha = set.lods.first().map(|m| m.color[3]).unwrap_or(1.0);
+                let mut ts = transform_block_mesh_lod_set(set, accum);
+                // Re-resolve colour against the INSERT context: a block-internal
+                // solid that is ByBlock or on layer "0" + ByLayer can't be
+                // coloured at cache-build time (no insert context there). (#221)
+                if let Some(c) = self.block_mesh_override_color(e, h, inherit, own_alpha) {
+                    for lod in &mut ts.lods {
+                        lod.color = c;
+                    }
+                }
+                out.push(ts);
             }
         }
     }
 
+    /// Background colour for the current layout (model vs paper).
+    fn current_bg(&self) -> [f32; 4] {
+        if self.current_layout != "Model" {
+            self.paper_bg_color
+        } else {
+            self.bg_color
+        }
+    }
+
+    /// Chain block-child colour inheritance into a nested INSERT, mirroring
+    /// `expand_insert`: ByBlock keeps the parent source; a nested insert on
+    /// layer "0" with ByLayer colour adopts the parent layer-0 target; else it
+    /// uses its own resolved colour / layer. Returned colours are bg-adapted.
+    fn chain_mesh_inherit(
+        &self,
+        ins: &acadrust::entities::Insert,
+        parent_ins_color: [f32; 4],
+        parent_l0: [f32; 4],
+    ) -> ([f32; 4], [f32; 4]) {
+        use acadrust::types::Color;
+        let bg = self.current_bg();
+        let child_ins_color = if ins.common.color == Color::ByBlock {
+            parent_ins_color
+        } else if ins.common.layer == "0" && ins.common.color == Color::ByLayer {
+            parent_l0
+        } else {
+            crate::scene::view::render::adapt_to_bg(
+                crate::scene::view::render::render_style_for(
+                    &self.document,
+                    &EntityType::Insert(ins.clone()),
+                )
+                .0,
+                bg,
+            )
+        };
+        let child_l0 = if ins.common.layer == "0" {
+            parent_l0
+        } else {
+            crate::scene::view::render::adapt_to_bg(
+                crate::scene::view::render::layer_render_style(&self.document, &ins.common.layer)
+                    .color,
+                bg,
+            )
+        };
+        (child_ins_color, child_l0)
+    }
+
+    /// Per-instance colour override for a block-internal solid mesh: ByBlock →
+    /// insert colour, layer-0 + ByLayer → insert-layer colour, else `None`
+    /// (keep the cached own-layer colour). Applies the same REFEDIT fade as
+    /// `recolor_meshes`, keyed on the inner solid handle. (#221)
+    fn block_mesh_override_color(
+        &self,
+        e: &EntityType,
+        h: Handle,
+        inherit: Option<([f32; 4], [f32; 4])>,
+        own_alpha: f32,
+    ) -> Option<[f32; 4]> {
+        let (ins_color, l0_color) = inherit?;
+        use acadrust::types::Color;
+        let common = e.common();
+        let mut c = if common.color == Color::ByBlock {
+            ins_color
+        } else if common.layer == "0" && common.color == Color::ByLayer {
+            // Inherit the insert layer's RGB but keep the solid's own alpha,
+            // matching the wire/hatch path (render_style_for_block_sub).
+            [l0_color[0], l0_color[1], l0_color[2], own_alpha]
+        } else {
+            return None;
+        };
+        if let Some(keep) = &self.refedit_keep {
+            if !keep.contains(&h) {
+                c = crate::scene::cache::block_cache::fade_toward_bg(c, self.current_bg());
+            }
+        }
+        Some(c)
+    }
+
     /// Hatches eligible for click / box / lasso hit-testing in the current
     /// layout. Filters out block-internal source hatches (stored in
     /// `self.hatches` at block-local coords for the block-defn position,
@@ -2572,7 +2687,7 @@ impl Scene {
                     continue;
                 }
                 let mut sets = Vec::new();
-                self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, &mut sets);
+                self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, None, &mut sets);
                 for set in sets {
                     if let Some(m) = set.lods.into_iter().next() {
                         block_owned.push((ins.common.handle, m));
@@ -2615,7 +2730,7 @@ impl Scene {
                 continue;
             }
             let mut sets = Vec::new();
-            self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, &mut sets);
+            self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, None, &mut sets);
             let hit = sets.iter().any(|set| {
                 set.lods.first().map_or(false, |m| {
                     !pick::hit_test::mesh_box_hit(
@@ -2660,7 +2775,7 @@ impl Scene {
                 continue;
             }
             let mut sets = Vec::new();
-            self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, &mut sets);
+            self.expand_block_meshes(&ins.block_name, &ins.get_transform(), 0, None, &mut sets);
             let hit = sets.iter().any(|set| {
                 set.lods.first().map_or(false, |m| {
                     !pick::hit_test::mesh_poly_hit(

src/scene/view/render.rs

@@ -533,26 +533,65 @@ pub(in crate::scene) fn render_style_for(
                 .unwrap_or(&LineWeight::Default),
             _ => ew,
         };
-        const MM_TO_PX: f32 = 96.0 / 25.4;
-        // CAD apps display model-space lineweights larger than their true
-        // physical size so the gradations stay legible on screen — at true
-        // scale a 0.5 mm line is ~2 px and is indistinguishable from thinner
-        // weights (which all floor to 1 px). Apply the same legibility boost so
-        // weights are pronounced and tell apart, matching other DWG editors.
-        // (#147)
-        const LWT_DISPLAY_BOOST: f32 = 2.0;
-        resolved
-            .millimeters()
-            .map(|mm| (mm as f32 * MM_TO_PX * LWT_DISPLAY_BOOST).max(1.0))
-            .unwrap_or(1.0)
+        lineweight_to_px(resolved)
     };
 
     (entity_color, pattern_length, pattern, line_weight_px, aci)
 }
 
-/// Like `render_style_for` but resolves ByBlock properties by inheriting from
-/// the INSERT entity's already-resolved style. Call this for exploded block
-/// sub-entities so that ByBlock color/linetype/lineweight propagate correctly.
+/// Resolved render style used as the inheritance source for a block child's
+/// ByBlock properties (the INSERT's own style) or its layer-0 properties (the
+/// INSERT's *layer* style). Bundled so it threads through the block-expansion
+/// call chain as a single value.
+#[derive(Clone, Copy, Debug)]
+pub struct InheritStyle {
+    pub color: [f32; 4],
+    pub pat_len: f32,
+    pub pat: [f32; 8],
+    pub lw_px: f32,
+}
+
+/// Convert a concrete (already layer-resolved) lineweight to display pixels.
+pub(crate) fn lineweight_to_px(lw: &LineWeight) -> f32 {
+    const MM_TO_PX: f32 = 96.0 / 25.4;
+    // CAD apps display model-space lineweights larger than their true physical
+    // size so the gradations stay legible on screen — at true scale a 0.5 mm
+    // line is ~2 px and is indistinguishable from thinner weights (which all
+    // floor to 1 px). Apply the same legibility boost so weights are pronounced
+    // and tell apart, matching other DWG editors. (#147)
+    const LWT_DISPLAY_BOOST: f32 = 2.0;
+    lw.millimeters()
+        .map(|mm| (mm as f32 * MM_TO_PX * LWT_DISPLAY_BOOST).max(1.0))
+        .unwrap_or(1.0)
+}
+
+/// Resolve a layer's own color / linetype / lineweight to concrete render
+/// values — what a fully-ByLayer entity on that layer would draw as. Used for
+/// the layer-0 block rule: a block child on layer "0" inherits the block
+/// reference's layer through this. Color is returned RAW (background adaptation
+/// happens at emit time). Falls back to white / Continuous / 1 px when the
+/// layer is missing.
+pub(crate) fn layer_render_style(document: &CadDocument, layer_name: &str) -> InheritStyle {
+    let layer = document.layers.get(layer_name);
+    let color = layer.map(|l| &l.color).unwrap_or(&AcadColor::WHITE);
+    let [r, g, b, _] = tess_util::aci_to_rgba(color);
+    let lt_name = layer.map(|l| l.line_type.as_str()).unwrap_or("Continuous");
+    let lt_scale = document.header.linetype_scale as f32;
+    let (pat_len, pat) = resolve_pattern(&document.line_types, lt_name, lt_scale);
+    let lw = layer.map(|l| &l.line_weight).unwrap_or(&LineWeight::Default);
+    InheritStyle {
+        color: [r, g, b, 1.0],
+        pat_len,
+        pat,
+        lw_px: lineweight_to_px(lw),
+    }
+}
+
+/// Like `render_style_for` but resolves a block sub-entity's inherited
+/// properties: ByBlock inherits the INSERT's style, and (the layer-0 rule) a
+/// sub-entity on layer "0" with ByLayer properties inherits the INSERT's
+/// *layer* style (`l0`). Explicit properties always win. Call this for
+/// exploded block sub-entities so color/linetype/lineweight propagate right.
 pub(crate) fn render_style_for_block_sub(
     document: &CadDocument,
     e: &EntityType,
@@ -560,24 +599,35 @@ pub(crate) fn render_style_for_block_sub(
     insert_pat_len: f32,
     insert_pat: [f32; 8],
     insert_lw_px: f32,
+    l0: InheritStyle,
 ) -> ([f32; 4], f32, [f32; 8], f32, u8) {
     let (color, pat_len, pat, lw_px, aci) = render_style_for(document, e);
     let common = e.common();
+    let on_l0 = common.layer == "0";
 
     let final_color = if common.color == AcadColor::ByBlock {
         insert_color
+    } else if on_l0 && common.color == AcadColor::ByLayer {
+        // Inherit the insert layer's RGB but keep the child's own transparency.
+        [l0.color[0], l0.color[1], l0.color[2], color[3]]
     } else {
         color
     };
 
+    let lt_bylayer =
+        common.linetype.is_empty() || common.linetype.eq_ignore_ascii_case("bylayer");
     let (final_pat_len, final_pat) = if common.linetype.eq_ignore_ascii_case("byblock") {
         (insert_pat_len, insert_pat)
+    } else if on_l0 && lt_bylayer {
+        (l0.pat_len, l0.pat)
     } else {
         (pat_len, pat)
     };
 
     let final_lw = if matches!(common.line_weight, LineWeight::ByBlock) {
         insert_lw_px
+    } else if on_l0 && matches!(common.line_weight, LineWeight::ByLayer | LineWeight::Default) {
+        l0.lw_px
     } else {
         lw_px
     };
@@ -1013,3 +1063,93 @@ fn split_face3d_wires(
     }
     (face3d, others)
 }
+
+// ── Layer-0 block inheritance (#221) ──────────────────────────────────────
+// A block child on layer "0" with ByLayer properties inherits the block
+// reference's *layer*; every other layer is "sticky" (keeps its own layer);
+// ByBlock inherits the insert's own style; explicit properties always win.
+#[cfg(test)]
+mod layer0_inherit_tests {
+    use super::*;
+    use acadrust::entities::Line;
+    use acadrust::tables::Layer;
+    use acadrust::types::{Color, Transparency};
+
+    // ACI: 1 = red, 3 = green, 7 = white. Distinct, so the assertions below
+    // can tell "inherited the insert layer" from "kept layer 0".
+    fn doc() -> CadDocument {
+        let mut d = CadDocument::new();
+        let mut walls = Layer::new("Walls");
+        walls.color = Color::Index(1); // red
+        d.layers.add_or_replace(walls);
+        let mut zero = Layer::new("0");
+        zero.color = Color::Index(7); // white
+        d.layers.add_or_replace(zero);
+        let mut other = Layer::new("Other");
+        other.color = Color::Index(3); // green
+        d.layers.add_or_replace(other);
+        d
+    }
+
+    fn child(layer: &str, color: Color) -> EntityType {
+        let mut l = Line::new();
+        l.common.layer = layer.to_string();
+        l.common.color = color;
+        EntityType::Line(l)
+    }
+
+    fn resolve(d: &CadDocument, e: &EntityType, ins: [f32; 4]) -> [f32; 4] {
+        // Insert sits on "Walls"; its layer style is the layer-0 target.
+        let l0 = layer_render_style(d, "Walls");
+        render_style_for_block_sub(d, e, ins, l0.pat_len, l0.pat, l0.lw_px, l0).0
+    }
+
+    #[test]
+    fn layer0_bylayer_inherits_insert_layer() {
+        let d = doc();
+        let walls = layer_render_style(&d, "Walls").color;
+        let zero = layer_render_style(&d, "0").color;
+        let c = resolve(&d, &child("0", Color::ByLayer), walls);
+        assert_eq!(&c[..3], &walls[..3], "layer-0 child must show the insert's layer (Walls)");
+        assert_ne!(&c[..3], &zero[..3], "layer-0 child must NOT show layer 0's own color");
+    }
+
+    #[test]
+    fn nonzero_layer_is_sticky() {
+        let d = doc();
+        let walls = layer_render_style(&d, "Walls").color;
+        let other = layer_render_style(&d, "Other").color;
+        let c = resolve(&d, &child("Other", Color::ByLayer), walls);
+        assert_eq!(&c[..3], &other[..3], "a child on a normal layer keeps its own layer");
+    }
+
+    #[test]
+    fn byblock_inherits_insert_color() {
+        let d = doc();
+        let ins = [0.2, 0.4, 0.6, 1.0];
+        let c = resolve(&d, &child("0", Color::ByBlock), ins);
+        assert_eq!(&c[..3], &ins[..3], "ByBlock child uses the insert's color");
+    }
+
+    #[test]
+    fn explicit_color_wins_even_on_layer0() {
+        let d = doc();
+        let walls = layer_render_style(&d, "Walls").color;
+        let green = tess_util::aci_to_rgba(&Color::Index(3));
+        let c = resolve(&d, &child("0", Color::Index(3)), walls);
+        assert_eq!(&c[..3], &green[..3], "an explicit color must win even on layer 0");
+    }
+
+    #[test]
+    fn layer0_preserves_child_transparency() {
+        let d = doc();
+        let walls = layer_render_style(&d, "Walls").color;
+        let mut l = Line::new();
+        l.common.layer = "0".to_string();
+        l.common.color = Color::ByLayer;
+        l.common.transparency = Transparency::from_percent(0.5); // 50% transparent
+        let c = resolve(&d, &EntityType::Line(l), walls);
+        assert_eq!(&c[..3], &walls[..3], "RGB inherited from the insert layer");
+        assert!((c[3] - 0.5).abs() < 0.02, "child's own 50% transparency is kept, got {}", c[3]);
+    }
+}