gui: Settings toggle to hide the host QR-code panel

Adds a `show_qr` preference (default on) to GuiSettings, with a
checkbox in Settings and a corresponding gate on the host-screen render.
Persists to config.toml alongside the existing close-to-tray setting.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/common/config.rs

@@ -20,13 +20,31 @@ pub struct Config {
 }
 
 /// Preferences for the `pixelpass --gui` front-end.
-#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct GuiSettings {
     /// When true, the window's close button hides the app to the system tray
     /// (keeping any live stream running) instead of quitting. Defaults to
     /// false — closing quits, which is what people expect.
     #[serde(default)]
     pub close_to_tray: bool,
+    /// When true, the host screen renders a QR-code panel for the ticket.
+    /// Defaults to true; the toggle exists for users who prefer the plain
+    /// text-only host screen.
+    #[serde(default = "default_true")]
+    pub show_qr: bool,
+}
+
+impl Default for GuiSettings {
+    fn default() -> Self {
+        Self {
+            close_to_tray: false,
+            show_qr: true,
+        }
+    }
+}
+
+fn default_true() -> bool {
+    true
 }
 
 /// Result of the first-run upstream measurement.

src/gui/mod.rs

@@ -596,16 +596,17 @@ pub fn run() -> anyhow::Result<()> {
     };
     // The tray runs on its own thread and wakes us via the proxy.
     let tray = tray::start(proxy.clone());
-    let close_to_tray = crate::common::config::load()
-        .map(|c| c.gui.close_to_tray)
-        .unwrap_or(false);
+    let gui_settings = crate::common::config::load()
+        .map(|c| c.gui)
+        .unwrap_or_default();
 
     let state = PixelPassApp {
         screen: Screen::default(),
         host: HostState::default(),
         viewer: ViewerState::default(),
         tray,
-        close_to_tray,
+        close_to_tray: gui_settings.close_to_tray,
+        show_qr: gui_settings.show_qr,
         waker,
     };
     let mut app = App {
@@ -691,6 +692,14 @@ fn persist_close_to_tray(value: bool) {
     }
 }
 
+fn persist_show_qr(value: bool) {
+    let mut cfg = crate::common::config::load().unwrap_or_default();
+    cfg.gui.show_qr = value;
+    if let Err(e) = crate::common::config::save(&cfg) {
+        tracing::warn!("failed to save settings: {e}");
+    }
+}
+
 /// Which screen the single window is currently showing.
 #[derive(Default, PartialEq)]
 enum Screen {
@@ -833,6 +842,9 @@ struct PixelPassApp {
     /// hides to the tray instead of quitting. Loaded at startup, written on
     /// toggle in Settings.
     close_to_tray: bool,
+    /// Persisted preference: render the QR-code panel on the host screen.
+    /// Defaults to on; toggled in Settings.
+    show_qr: bool,
     /// Wakes the winit loop when a spawned child emits/exits.
     waker: Waker,
 }
@@ -938,6 +950,21 @@ impl PixelPassApp {
             .weak(),
         );
 
+        ui.add_space(12.0);
+        let qr_resp = ui.checkbox(&mut self.show_qr, "Show QR-code panel on the host screen");
+        if qr_resp.changed() {
+            persist_show_qr(self.show_qr);
+        }
+        ui.add_space(4.0);
+        ui.label(
+            egui::RichText::new(
+                "Off: the host screen shows only the ticket text. \
+                 Useful when both ends are computers and the QR is just extra clutter.",
+            )
+            .small()
+            .weak(),
+        );
+
         // The option does nothing without a tray to hide into; say so plainly.
         if !self.tray.as_ref().is_some_and(TrayHandle::registered) {
             ui.add_space(8.0);
@@ -1127,8 +1154,10 @@ impl PixelPassApp {
             // Lazy QR build: first draw after a Ticket event has `qr_texture =
             // None`, so we encode the ticket and load the texture once. The
             // 4-module quiet zone (white border) matters — phone scanners reject
-            // QR codes flush against a non-white edge.
-            if self.host.qr_texture.is_none()
+            // QR codes flush against a non-white edge. Skipped when the user
+            // disabled the QR panel in Settings.
+            if self.show_qr
+                && self.host.qr_texture.is_none()
                 && let Ok(code) = qrcode::QrCode::new(ticket.as_bytes())
             {
                 let w = code.width();
@@ -1150,7 +1179,9 @@ impl PixelPassApp {
                     egui::TextureOptions::NEAREST,
                 ));
             }
-            if let Some(tex) = &self.host.qr_texture {
+            if self.show_qr
+                && let Some(tex) = &self.host.qr_texture
+            {
                 ui.add_space(8.0);
                 ui.add(egui::Image::new(tex).fit_to_exact_size(egui::vec2(200.0, 200.0)));
             }