feat(statusbar): transparency-display toggle (TPY pill)

Add a transparency_enable uniform read by the wire shader: when the new
TPY pill is off, every line is forced opaque; when on, baked entity
transparency shows through. Toggling is a uniform write, no retessellate
(same mechanism as the lineweight-display toggle). Pill is toggleable
from the status-bar customization menu.

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

src/app/mod.rs

@@ -750,6 +750,8 @@ pub enum Message {
     ToggleStatusPill(crate::ui::statusbar_config::StatusPill),
     /// Toggle clean-screen mode (hide ribbon + side panels).
     ToggleCleanScreen,
+    /// Toggle whether entity transparency is shown on screen.
+    ToggleTransparencyDisplay,
     /// Toggle the drawing-units picker open/closed.
     ToggleUnitsPopup,
     /// Close the drawing-units picker.

src/app/update.rs

@@ -3582,6 +3582,14 @@ impl OpenCADStudio {
                 self.clean_screen ^= true;
                 Task::none()
             }
+            Message::ToggleTransparencyDisplay => {
+                let i = self.active_tab;
+                if i < self.tabs.len() {
+                    // No retessellate — the wire shader reads the flag from uniforms.
+                    self.tabs[i].scene.transparency_display ^= true;
+                }
+                Task::none()
+            }
             Message::ToggleUnitsPopup => {
                 self.units_popup_open ^= true;
                 Task::none()

src/app/view.rs

@@ -1162,6 +1162,7 @@ impl OpenCADStudio {
                         tab.scene.document.header.insertion_units,
                         self.units_popup_open,
                         tab.scene.is_isolation_active(),
+                        tab.scene.transparency_display,
                         &self.statusbar_config,
                     )
                 })

src/scene/mod.rs

@@ -553,6 +553,9 @@ pub struct Scene {
     /// `tessellate_block`'s visibility test skips these, so they neither
     /// render nor hit-test until isolation ends.
     pub hidden: HashSet<Handle>,
+    /// Whether entity transparency is honoured on screen. When false the
+    /// wire shader forces every line opaque (a uniform toggle, no retessellate).
+    pub transparency_display: bool,
     /// In-progress preview wires while a command is active (rubber-band + object ghosts).
     pub preview_wires: Vec<WireModel>,
     /// Committed-segment wire drawn during multi-point commands (normal colour).
@@ -698,6 +701,7 @@ impl Scene {
             document: CadDocument::new(),
             selected: HashSet::new(),
             hidden: HashSet::new(),
+            transparency_display: true,
             preview_wires: vec![],
             interim_wire: None,
             camera_generation: 0,

src/scene/pipeline/uniforms.rs

@@ -19,9 +19,13 @@ pub struct Uniforms {
     /// triangle gets a uniform shade (FlatShaded mode); 0.0 → keeps the
     /// per-vertex normal interpolation (GouraudShaded-style).
     pub flat_shade: f32,
+    /// Transparency-display toggle (1.0 = honour entity transparency,
+    /// 0.0 = force opaque). Read by the wire shader so the toggle does not
+    /// require a retessellate.
+    pub transparency_enable: f32,
     /// Pads the struct to 112 B (next multiple of 16) so wgpu's uniform
     /// alignment rules are satisfied.
-    pub _pad: [f32; 3],
+    pub _pad: [f32; 2],
 }
 
 impl Uniforms {
@@ -39,7 +43,8 @@ impl Uniforms {
             world_per_pixel,
             lwdisplay_enable: if lwdisplay_enable { 1.0 } else { 0.0 },
             flat_shade: 0.0,
-            _pad: [0.0; 3],
+            transparency_enable: 1.0,
+            _pad: [0.0; 2],
         }
     }
 }

src/scene/render.rs

@@ -636,6 +636,7 @@ impl Scene {
         uniforms.view_proj = crop_view_proj(uniforms.view_proj, uo, vo, us, vs);
         uniforms.viewport_size = [visible_w, visible_h];
         uniforms.flat_shade = if flags.flat_shade { 1.0 } else { 0.0 };
+        uniforms.transparency_enable = if self.transparency_display { 1.0 } else { 0.0 };
 
         // `screen_rect` carries the *visible* sub-rectangle in normalized
         // canvas coords — that's what `Pipeline::prepare` uses to size

src/shaders/wire.wgsl

@@ -22,6 +22,12 @@ struct Uniforms {
     // per-instance baked half_width. Lets the LWT button switch without
     // retessellating.
     lwdisplay_enable: f32,
+    // Mesh flat-shade flag (unused here; kept so the field offsets match
+    // the shared Uniforms buffer layout).
+    flat_shade: f32,
+    // Transparency-display toggle: 1.0 = honour baked alpha, 0.0 = force
+    // every line opaque.
+    transparency_enable: f32,
 }
 @group(0) @binding(0) var<uniform> u: Uniforms;
 
@@ -156,5 +162,7 @@ fn in_dash(dist: f32, pat_len: f32, p0: vec4<f32>, p1: vec4<f32>) -> bool {
             }
         }
     }
-    return in.color;
+    // Transparency display off → force the line opaque.
+    let alpha = select(1.0, in.color.a, u.transparency_enable > 0.5);
+    return vec4<f32>(in.color.rgb, alpha);
 }

src/ui/statusbar.rs

@@ -61,6 +61,8 @@ impl StatusBar {
         units_popup_open: bool,
         // True when objects are hidden by Isolate / Hide.
         isolation_active: bool,
+        // Whether entity transparency is shown (Transparency pill state).
+        transparency_display: bool,
         // Which pills the user has chosen to show on the bar.
         config: &'a StatusBarConfig,
     ) -> Element<'a, Message> {
@@ -175,6 +177,16 @@ impl StatusBar {
                 "Drawing Units (INSUNITS)\nClick to change",
             ));
         }
+        if vis(StatusPill::Transparency) {
+            right_status = right_status.push(tip(
+                toggle_pill(
+                    "TPY",
+                    transparency_display,
+                    Message::ToggleTransparencyDisplay,
+                ),
+                "Show Transparency\nForce opaque when off",
+            ));
+        }
         if vis(StatusPill::Isolate) {
             right_status = right_status.push(tip(
                 toggle_pill("ISO", isolation_active, Message::ToggleIsolatePopup),

src/ui/statusbar_config.rs

@@ -23,6 +23,7 @@ pub enum StatusPill {
     Space,
     Scale,
     Units,
+    Transparency,
     Isolate,
     Vp,
     CleanScreen,
@@ -44,6 +45,7 @@ impl StatusPill {
         StatusPill::Space,
         StatusPill::Scale,
         StatusPill::Units,
+        StatusPill::Transparency,
         StatusPill::Isolate,
         StatusPill::Vp,
         StatusPill::CleanScreen,
@@ -64,6 +66,7 @@ impl StatusPill {
             StatusPill::Space => "space",
             StatusPill::Scale => "scale",
             StatusPill::Units => "units",
+            StatusPill::Transparency => "transparency",
             StatusPill::Isolate => "isolate",
             StatusPill::Vp => "vp",
             StatusPill::CleanScreen => "cleanscreen",
@@ -85,6 +88,7 @@ impl StatusPill {
             StatusPill::Space => "Model/Paper Space",
             StatusPill::Scale => "Annotation Scale",
             StatusPill::Units => "Drawing Units",
+            StatusPill::Transparency => "Show Transparency",
             StatusPill::Isolate => "Isolate Objects",
             StatusPill::Vp => "Viewport Count",
             StatusPill::CleanScreen => "Clean Screen",