perf(wire): move LWDISPLAY toggle from CPU rebake to wire shader uniform

LWDISPLAY (Show Lineweight) flipping the toggle no longer triggers a full
retessellate. `render_style_for` always bakes the entity's resolved (layer-
inherited) lineweight, and the wire shader reads `Uniforms.lwdisplay_enable`
to either honour the per-vertex half_width or collapse the quad to a 1 px line.

Side effect: PDF export now uses the real lineweight regardless of LWDISPLAY,
matching AutoCAD's plot semantics (LWDISPLAY only affects screen render).

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/app/commands.rs

@@ -4522,7 +4522,7 @@ impl H7CAD {
                     Ok(Some(v)) => {
                         self.push_undo_snapshot(i, "LWDISPLAY");
                         self.tabs[i].scene.document.header.lineweight_display = v;
-                        self.tabs[i].scene.bump_geometry();
+                        // No retessellate — the wire shader honours the flag via uniforms.
                         self.tabs[i].dirty = true;
                         self.command_line.push_output(&format!(
                             "LWDISPLAY {}",

src/app/update.rs

@@ -2514,7 +2514,7 @@ impl H7CAD {
                 if i < self.tabs.len() {
                     let h = &mut self.tabs[i].scene.document.header;
                     h.lineweight_display = !h.lineweight_display;
-                    self.tabs[i].scene.bump_geometry();
+                    // No retessellate — the wire shader reads the flag from uniforms.
                     self.tabs[i].dirty = true;
                 }
                 Task::none()

src/scene/pipeline/uniforms.rs

@@ -11,11 +11,13 @@ pub struct Uniforms {
     /// hatch shader to substitute solid fill when pattern line spacing
     /// falls below ~2 px (Phase 3.3 LOD).
     pub world_per_pixel: f32,
-    pub _pad: f32,
+    /// LWDISPLAY toggle (1.0 = show lineweights, 0.0 = force 1 px).
+    /// Read by the wire shader so the toggle does not require a retessellate.
+    pub lwdisplay_enable: f32,
 }
 
 impl Uniforms {
-    pub fn new(camera: &Camera, bounds: Rectangle) -> Self {
+    pub fn new(camera: &Camera, bounds: Rectangle, lwdisplay_enable: bool) -> Self {
         let half_h = camera.ortho_size();
         let world_per_pixel = if bounds.height > 0.0 {
             (2.0 * half_h) / bounds.height
@@ -27,7 +29,7 @@ impl Uniforms {
             camera_pos: camera.position_vec4(),
             viewport_size: [bounds.width, bounds.height],
             world_per_pixel,
-            _pad: 0.0,
+            lwdisplay_enable: if lwdisplay_enable { 1.0 } else { 0.0 },
         }
     }
 }

src/scene/render.rs

@@ -253,27 +253,24 @@ pub(super) fn render_style_for(
     let (pattern_length, pattern) = resolve_pattern(&document.line_types, lt_name, lt_scale);
 
     let line_weight_px = {
-        // LWDISPLAY (header.lineweight_display): when false, every entity
-        // draws at the 1-pixel base width regardless of its assigned weight.
-        // AutoCAD's "Show Lineweight" toggle maps onto this header var.
-        if !document.header.lineweight_display {
-            1.0
-        } else {
-            let ew = &e.common().line_weight;
-            let resolved = match ew {
-                LineWeight::ByLayer | LineWeight::ByBlock | LineWeight::Default => document
-                    .layers
-                    .get(layer_name)
-                    .map(|l| &l.line_weight)
-                    .unwrap_or(&LineWeight::Default),
-                _ => ew,
-            };
-            const MM_TO_PX: f32 = 96.0 / 25.4;
-            resolved
-                .millimeters()
-                .map(|mm| (mm as f32 * MM_TO_PX).max(1.0))
-                .unwrap_or(1.0)
-        }
+        // LWDISPLAY is no longer evaluated here — the toggle is now applied in
+        // the wire shader via `Uniforms.lwdisplay_enable`, so we always bake the
+        // entity's resolved (layer-inherited) weight. Toggling lineweight
+        // visibility costs only a uniform write, not a retessellate.
+        let ew = &e.common().line_weight;
+        let resolved = match ew {
+            LineWeight::ByLayer | LineWeight::ByBlock | LineWeight::Default => document
+                .layers
+                .get(layer_name)
+                .map(|l| &l.line_weight)
+                .unwrap_or(&LineWeight::Default),
+            _ => ew,
+        };
+        const MM_TO_PX: f32 = 96.0 / 25.4;
+        resolved
+            .millimeters()
+            .map(|mm| (mm as f32 * MM_TO_PX).max(1.0))
+            .unwrap_or(1.0)
     };
 
     (entity_color, pattern_length, pattern, line_weight_px, aci)
@@ -376,7 +373,7 @@ impl Scene {
             wipeout_hatches: self.wipeout_models_arc(),
             images: self.images_arc(),
             meshes: self.meshes_arc(),
-            uniforms: Uniforms::new(&cam, bounds),
+            uniforms: Uniforms::new(&cam, bounds, self.document.header.lineweight_display),
             cam_rotation: cam.view_rotation_mat(),
             hover_region,
             bg_color,
@@ -420,7 +417,7 @@ impl Scene {
             wipeout_hatches: self.wipeout_models_arc(),
             images: self.images_arc(),
             meshes: self.meshes_arc(),
-            uniforms: Uniforms::new(&cam, bounds),
+            uniforms: Uniforms::new(&cam, bounds, self.document.header.lineweight_display),
             cam_rotation: cam.view_rotation_mat(),
             hover_region,
             bg_color: self.bg_color,

src/shaders/wire.wgsl

@@ -11,10 +11,13 @@
 //   • pat0/pat1 encode up to 8 elements: positive=dash, negative=gap.
 
 struct Uniforms {
-    view_proj:     mat4x4<f32>,
-    camera_pos:    vec4<f32>,
-    viewport_size: vec2<f32>,
-    _pad:          vec2<f32>,
+    view_proj:        mat4x4<f32>,
+    camera_pos:       vec4<f32>,
+    viewport_size:    vec2<f32>,
+    world_per_pixel:  f32,
+    // LWDISPLAY toggle: 0.0 = force 1 px (half_width 0.5), 1.0 = use per-vertex
+    // baked half_width. Lets the LWT button switch without retessellating.
+    lwdisplay_enable: f32,
 }
 @group(0) @binding(0) var<uniform> u: Uniforms;
 
@@ -70,8 +73,11 @@ struct VertexOut {
     // Select the clip-space position for this vertex's endpoint.
     let clip_pos = mix(clip_a, clip_b, in.which_end);
 
+    // LWDISPLAY off → collapse to a 1-pixel-wide line (half_width = 0.5).
+    let hw = select(0.5, in.half_width, u.lwdisplay_enable > 0.5);
+
     // Offset in clip space (multiply by w to un-apply perspective division).
-    let ndc_offset = perp_ndc * in.half_width * in.side;
+    let ndc_offset = perp_ndc * hw * in.side;
     let final_clip = clip_pos + vec4<f32>(ndc_offset * clip_pos.w, 0.0, 0.0);
 
     var out: VertexOut;