diff --git a/src/entities/lwpolyline.rs b/src/entities/lwpolyline.rs
index e51bc8bb8..f74588c50 100644
--- a/src/entities/lwpolyline.rs
+++ b/src/entities/lwpolyline.rs
@@ -964,7 +964,16 @@ fn apply_geom_prop(pline: &mut LwPolyline, field: &str, value: &str) {
     };
     match field {
         "elevation" => pline.elevation = v,
-        "global_width" => pline.constant_width = v,
+        "global_width" if v.is_finite() && v >= 0.0 => {
+            pline.constant_width = v;
+            // Global width replaces every segment override. Keeping old
+            // start/end values would make this editable row appear to work
+            // while the renderer continued using the stale per-segment data.
+            for vertex in &mut pline.vertices {
+                vertex.start_width = 0.0;
+                vertex.end_width = 0.0;
+            }
+        }
         "vertex_x" => {
             if let Some(vtx) = pline.vertices.get_mut(vi) {
                 vtx.location.x = v;
@@ -975,12 +984,28 @@ fn apply_geom_prop(pline: &mut LwPolyline, field: &str, value: &str) {
                 vtx.location.y = v;
             }
         }
-        "start_width" => {
+        "start_width" if v.is_finite() && v >= 0.0 => {
+            if pline.constant_width > 0.0 {
+                let width = pline.constant_width;
+                for vertex in &mut pline.vertices {
+                    vertex.start_width = width;
+                    vertex.end_width = width;
+                }
+                pline.constant_width = 0.0;
+            }
             if let Some(vtx) = pline.vertices.get_mut(vi) {
                 vtx.start_width = v;
             }
         }
-        "end_width" => {
+        "end_width" if v.is_finite() && v >= 0.0 => {
+            if pline.constant_width > 0.0 {
+                let width = pline.constant_width;
+                for vertex in &mut pline.vertices {
+                    vertex.start_width = width;
+                    vertex.end_width = width;
+                }
+                pline.constant_width = 0.0;
+            }
             if let Some(vtx) = pline.vertices.get_mut(vi) {
                 vtx.end_width = v;
             }
diff --git a/src/scene/pipeline/uniforms.rs b/src/scene/pipeline/uniforms.rs
index c493081bc..29326992c 100644
--- a/src/scene/pipeline/uniforms.rs
+++ b/src/scene/pipeline/uniforms.rs
@@ -25,7 +25,8 @@ pub struct Uniforms {
     /// zooming inside MSPACE changes one scalar instead of re-tessellating and
     /// re-uploading every dashed wire.
     pub linetype_scale: f32,
-    /// Pads the struct to the uniform alignment required by wgpu.
+    /// FILLMODE toggle. Wire shaders use this slot to draw wide polylines as
+    /// boundary outlines when fills are disabled.
     pub _pad: f32,
 
     // ── Relative-to-eye (double-single) additions ───────────────────────────
diff --git a/src/scene/view/render.rs b/src/scene/view/render.rs
index 29a9f25cc..b09fb5dbd 100644
--- a/src/scene/view/render.rs
+++ b/src/scene/view/render.rs
@@ -3527,6 +3527,7 @@ impl Scene {
         };
         let mut uniforms =
             Uniforms::new(&inst.camera, full_bounds, self.document.header.lineweight_display);
+        uniforms._pad = if self.document.header.fill_mode { 1.0 } else { 0.0 };
         if self.document.header.paper_space_linetype_scaling
             && !inst.paper_sheet
             && inst.tile_idx.is_none()
diff --git a/src/shaders/block_wire.wgsl b/src/shaders/block_wire.wgsl
index 29e5bd256..79231f87f 100644
--- a/src/shaders/block_wire.wgsl
+++ b/src/shaders/block_wire.wgsl
@@ -5,7 +5,7 @@ struct Uniforms {
     flat_shade: f32,
     transparency_enable: f32,
     linetype_scale: f32,
-    _pad: f32,
+    fillmode_enable: f32,
     view_rot: mat4x4<f32>,
     eye_high: vec3<f32>,
     _pad_eh: f32,
@@ -58,6 +58,7 @@ struct VertexOut {
     @location(7) @interpolate(flat) align_total: f32,
     @location(8) cap: vec2<f32>,
     @location(9) @interpolate(flat) cap_ends: vec3<f32>,
+    @location(10) @interpolate(flat) world_band: f32,
 }
 
 fn resolve_hw(taper_ratio: f32, world_hw: f32, px_hw: f32) -> f32 {
@@ -175,6 +176,11 @@ fn vs_main(@builtin(vertex_index) vertex_index: u32, in: VertexIn) -> VertexOut
         half_width * side,
     );
     out.cap_ends = vec3<f32>(segment_length, half_width_a, half_width_b);
+    out.world_band = select(
+        0.0,
+        1.0,
+        wire_const.world_half_width > 0.0 || in.taper_ratio.x > 0.0 || in.taper_ratio.y > 0.0
+    );
     return out;
 }
 
@@ -244,10 +250,28 @@ fn clipped_cap(cap: vec2<f32>, ends: vec3<f32>) -> bool {
     return false;
 }
 
+fn band_interior_clipped(in: VertexOut) -> bool {
+    if u.fillmode_enable > 0.5 || in.world_band < 0.5 {
+        return false;
+    }
+    if in.cap.x < 0.0 || in.cap.x > in.cap_ends.x {
+        return true;
+    }
+    var along = 0.0;
+    if in.cap_ends.x > 1e-4 {
+        along = clamp(in.cap.x / in.cap_ends.x, 0.0, 1.0);
+    }
+    let half_width = mix(in.cap_ends.y, in.cap_ends.z, along);
+    return abs(in.cap.y) < max(half_width - 1.0, 0.0);
+}
+
 fn visible_fragment(in: VertexOut) -> bool {
     if clipped_cap(in.cap, in.cap_ends) {
         return false;
     }
+    if band_interior_clipped(in) {
+        return false;
+    }
     if in.pattern_length > 0.0 && in.min_elem >= u.world_per_pixel {
         return in_dash(
             in.distance,
diff --git a/src/shaders/wire.wgsl b/src/shaders/wire.wgsl
index c8fac6521..747fb5740 100644
--- a/src/shaders/wire.wgsl
+++ b/src/shaders/wire.wgsl
@@ -29,7 +29,7 @@ struct Uniforms {
     // every line opaque.
     transparency_enable: f32,
     linetype_scale: f32,
-    _pad: f32,
+    fillmode_enable: f32,
     // ── Relative-to-eye (double-single) ──────────────────────────────────
     // view_rot is the rotation-only view-projection; vertices subtract the eye
     // (eye_high + eye_low, two f32 emulating f64) before transforming, so the
@@ -94,6 +94,7 @@ struct VertexOut {
     @location(8)                    cap:            vec2<f32>,
     // (segment pixel length, end half-width at A, end half-width at B).
     @location(9) @interpolate(flat) cap_ends:       vec3<f32>,
+    @location(10) @interpolate(flat) world_band:    f32,
 }
 
 // Half-width of one segment end: a tapered band's own end width wins, then a
@@ -215,6 +216,7 @@ fn marker_relative(position_high: vec3<f32>, position_low: vec3<f32>, instance:
         + ext * hw * u.world_per_pixel;
     out.cap            = vec2<f32>(which_end * seg_len + ext * hw, hw * side);
     out.cap_ends       = vec3<f32>(seg_len, hw_a, hw_b);
+    out.world_band     = select(0.0, 1.0, in.misc.w > 0.0 || in.taper.x > 0.0 || in.taper.y > 0.0);
     out.pattern_length = in.dists.w * lt_scale;
     out.pat0           = in.pat0 * lt_scale;
     out.pat1           = in.pat1 * lt_scale;
@@ -287,6 +289,24 @@ fn cap_clipped(cap: vec2<f32>, cap_ends: vec3<f32>) -> bool {
     return false;
 }
 
+fn band_interior_clipped(in: VertexOut) -> bool {
+    if u.fillmode_enable > 0.5 || in.world_band < 0.5 {
+        return false;
+    }
+    // Wide-polyline fill off: retain a one-pixel line at both band edges.
+    // Segment cap overhangs are discarded; adjacent sampled segments meet at
+    // their shared endpoint without drawing an interior seam across the band.
+    if in.cap.x < 0.0 || in.cap.x > in.cap_ends.x {
+        return true;
+    }
+    var along = 0.0;
+    if in.cap_ends.x > 1e-4 {
+        along = clamp(in.cap.x / in.cap_ends.x, 0.0, 1.0);
+    }
+    let half_width = mix(in.cap_ends.y, in.cap_ends.z, along);
+    return abs(in.cap.y) < max(half_width - 1.0, 0.0);
+}
+
 @fragment fn fs_main(in: VertexOut) -> @location(0) vec4<f32> {
     // Negative pattern length is the persistent-arena tombstone sentinel.
     // Discard before cap/alpha work so deleted slabs cannot write color/depth.
@@ -296,6 +316,9 @@ fn cap_clipped(cap: vec2<f32>, cap_ends: vec3<f32>) -> bool {
     if cap_clipped(in.cap, in.cap_ends) {
         discard;
     }
+    if band_interior_clipped(in) {
+        discard;
+    }
     if in.pattern_length > 0.0 {
         // LOD: once the pattern's smallest feature drops below ~1 px
         // on screen, dash gaps alias / shimmer (or vanish completely)
@@ -323,6 +346,9 @@ fn cap_clipped(cap: vec2<f32>, cap_ends: vec3<f32>) -> bool {
     if cap_clipped(in.cap, in.cap_ends) {
         discard;
     }
+    if band_interior_clipped(in) {
+        discard;
+    }
     if in.pattern_length > 0.0 {
         if in.min_elem >= u.world_per_pixel {
             if !in_dash(in.distance, in.pattern_length, in.pat0, in.pat1, in.align_end, in.align_total) {
diff --git a/src/shaders/wire_indexed.wgsl b/src/shaders/wire_indexed.wgsl
index c62d92bd6..0e0acfdac 100644
--- a/src/shaders/wire_indexed.wgsl
+++ b/src/shaders/wire_indexed.wgsl
@@ -12,7 +12,7 @@ struct Uniforms {
     flat_shade: f32,
     transparency_enable: f32,
     linetype_scale: f32,
-    _pad: f32,
+    fillmode_enable: f32,
     view_rot:         mat4x4<f32>,
     eye_high:         vec3<f32>,
     _pad_eh:          f32,
@@ -71,6 +71,7 @@ struct VertexOut {
     @location(8)                    cap:            vec2<f32>,
     // (segment pixel length, end half-width at A, end half-width at B).
     @location(9) @interpolate(flat) cap_ends:       vec3<f32>,
+    @location(10) @interpolate(flat) world_band:    f32,
 }
 
 // Half-width of one segment end: a tapered band's own end width wins, then a
@@ -181,6 +182,7 @@ fn marker_relative(position_high: vec3<f32>, position_low: vec3<f32>, c: WireCon
         + ext * hw * u.world_per_pixel;
     out.cap            = vec2<f32>(which_end * seg_len + ext * hw, hw * side);
     out.cap_ends       = vec3<f32>(seg_len, hw_a, hw_b);
+    out.world_band     = select(0.0, 1.0, c.world_half_width > 0.0 || in.taper_ratio.x > 0.0 || in.taper_ratio.y > 0.0);
     out.pattern_length = c.pattern_length * lt_scale;
     out.pat0           = c.pat0 * lt_scale;
     out.pat1           = c.pat1 * lt_scale;
@@ -244,6 +246,21 @@ fn cap_clipped(cap: vec2<f32>, cap_ends: vec3<f32>) -> bool {
     return false;
 }
 
+fn band_interior_clipped(in: VertexOut) -> bool {
+    if u.fillmode_enable > 0.5 || in.world_band < 0.5 {
+        return false;
+    }
+    if in.cap.x < 0.0 || in.cap.x > in.cap_ends.x {
+        return true;
+    }
+    var along = 0.0;
+    if in.cap_ends.x > 1e-4 {
+        along = clamp(in.cap.x / in.cap_ends.x, 0.0, 1.0);
+    }
+    let half_width = mix(in.cap_ends.y, in.cap_ends.z, along);
+    return abs(in.cap.y) < max(half_width - 1.0, 0.0);
+}
+
 @fragment fn fs_main(in: VertexOut) -> @location(0) vec4<f32> {
     // Negative pattern length is the persistent-arena tombstone sentinel.
     // Discard before cap/alpha work so deleted slabs cannot write color/depth.
@@ -253,6 +270,9 @@ fn cap_clipped(cap: vec2<f32>, cap_ends: vec3<f32>) -> bool {
     if cap_clipped(in.cap, in.cap_ends) {
         discard;
     }
+    if band_interior_clipped(in) {
+        discard;
+    }
     if in.pattern_length > 0.0 {
         if in.min_elem >= u.world_per_pixel {
             if !in_dash(in.distance, in.pattern_length, in.pat0, in.pat1, in.align_end, in.align_total) {
@@ -274,6 +294,9 @@ fn cap_clipped(cap: vec2<f32>, cap_ends: vec3<f32>) -> bool {
     if cap_clipped(in.cap, in.cap_ends) {
         discard;
     }
+    if band_interior_clipped(in) {
+        discard;
+    }
     if in.pattern_length > 0.0 {
         if in.min_elem >= u.world_per_pixel {
             if !in_dash(in.distance, in.pattern_length, in.pat0, in.pat1, in.align_end, in.align_total) {