feat(engine): UI scale setting — 90/100/115/130% (Phase K)

Settings -> Accessibility gains a UI Scale row cycling four steps,
applied live through bevy::ui::UiScale: every menu, modal, and HUD
element scales while the table itself stays window-fit via
compute_layout. New Settings::ui_scale (serde default 1.0, sanitized
clamp to [0.9, 1.3]).

Safe-area anchors and modal scrim padding pre-divide physical insets
by the UI scale so post-multiplication lands exactly on the system
bars — without this, 90% would sink the bottom action bar into the
Android gesture zone. The anchor systems also re-run on UiScale
changes, not just inset changes.

Deferred from Phase K (noted in the doc): seeding the setting from the
Android system font scale on first run (needs JNI), and the 44px
touch-target audit (on-device).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_data/src/settings.rs

@@ -275,6 +275,14 @@ pub struct Settings {
     /// which marks the tip as unnecessary without showing it.
     #[serde(default)]
     pub shown_radial_menu_tip: bool,
+    /// Global UI scale multiplier applied to all UI chrome (HUD, modals,
+    /// action bar) — the table itself stays window-fit via
+    /// `compute_layout`. Cycles through 0.9 / 1.0 / 1.15 / 1.3 in
+    /// Settings → Accessibility; clamped to `[UI_SCALE_MIN,
+    /// UI_SCALE_MAX]` by [`Settings::sanitized`]. Older `settings.json`
+    /// files deserialize cleanly to `1.0` via the serde default.
+    #[serde(default = "default_ui_scale")]
+    pub ui_scale: f32,
     /// Custom public name displayed on the leaderboard. When `None`, the
     /// player's server `username` is used instead. Trimmed to 32 characters
     /// before submission. Older `settings.json` files written before this
@@ -383,6 +391,16 @@ fn default_replay_move_interval_secs() -> f32 {
     0.45
 }
 
+/// Lowest / highest UI scale the settings row offers; anything outside
+/// (hand-edited settings.json) clamps here on load.
+pub const UI_SCALE_MIN: f32 = 0.9;
+/// See [`UI_SCALE_MIN`].
+pub const UI_SCALE_MAX: f32 = 1.3;
+
+fn default_ui_scale() -> f32 {
+    1.0
+}
+
 fn default_matomo_site_id() -> u32 {
     1
 }
@@ -446,6 +464,7 @@ impl Default for Settings {
             last_seen_whats_new: String::new(),
             shown_stall_hint_tip: false,
             shown_radial_menu_tip: false,
+            ui_scale: default_ui_scale(),
             leaderboard_display_name: None,
             leaderboard_opted_in: false,
             take_from_foundation: true,
@@ -481,6 +500,7 @@ impl Settings {
             replay_move_interval_secs: self
                 .replay_move_interval_secs
                 .clamp(REPLAY_MOVE_INTERVAL_MIN_SECS, REPLAY_MOVE_INTERVAL_MAX_SECS),
+            ui_scale: self.ui_scale.clamp(UI_SCALE_MIN, UI_SCALE_MAX),
             selected_theme_id,
             ..self
         }

solitaire_engine/src/safe_area.rs

@@ -101,9 +101,10 @@ impl Plugin for SafeAreaInsetsPlugin {
 fn apply_safe_area_anchors(
     insets: Res<SafeAreaInsets>,
     windows: Query<&Window>,
+    ui_scale: Option<Res<UiScale>>,
     mut q: Query<(&SafeAreaAnchoredTop, &mut Node)>,
 ) {
-    if !insets.is_changed() {
+    if !insets.is_changed() && !ui_scale.as_ref().is_some_and(|s| s.is_changed()) {
         return;
     }
     // Android's WindowInsets API returns physical pixels; Bevy UI's Val::Px
@@ -119,19 +120,31 @@ fn apply_safe_area_anchors(
         );
     }
     let top_logical = raw_top.min(max_inset);
+    // `bevy::ui::UiScale` (Phase K) multiplies every Val::Px at layout
+    // time. `base_top` is UI chrome and SHOULD scale with the rest of
+    // the interface, but the system-bar inset is physical reality —
+    // pre-divide it so the post-multiplication offset stays exact.
+    let ui = effective_ui_scale(ui_scale.as_deref());
     for (anchor, mut node) in &mut q {
-        node.top = Val::Px(anchor.base_top + top_logical);
+        node.top = Val::Px(anchor.base_top + top_logical / ui);
     }
 }
 
+/// The live UI scale, defensively clamped — a zero or negative scale
+/// would flip or destroy the inset math.
+fn effective_ui_scale(ui_scale: Option<&UiScale>) -> f32 {
+    ui_scale.map_or(1.0, |s| s.0.max(0.1))
+}
+
 /// Re-applies `base_bottom + insets.bottom / scale` to every entity carrying
 /// [`SafeAreaAnchoredBottom`] whenever [`SafeAreaInsets`] changes.
 fn apply_safe_area_bottom_anchors(
     insets: Res<SafeAreaInsets>,
     windows: Query<&Window>,
+    ui_scale: Option<Res<UiScale>>,
     mut q: Query<(&SafeAreaAnchoredBottom, &mut Node)>,
 ) {
-    if !insets.is_changed() {
+    if !insets.is_changed() && !ui_scale.as_ref().is_some_and(|s| s.is_changed()) {
         return;
     }
     let scale = windows.iter().next().map_or(1.0, |w| w.scale_factor());
@@ -144,8 +157,12 @@ fn apply_safe_area_bottom_anchors(
         );
     }
     let bottom_logical = raw_bottom.min(max_inset);
+    // See `apply_safe_area_anchors`: the physical inset is pre-divided
+    // by the UI scale so a 90% setting can't sink the action bar into
+    // the gesture zone (and 130% doesn't over-inset it).
+    let ui = effective_ui_scale(ui_scale.as_deref());
     for (anchor, mut node) in &mut q {
-        node.bottom = Val::Px(anchor.base_bottom + bottom_logical);
+        node.bottom = Val::Px(anchor.base_bottom + bottom_logical / ui);
     }
 }
 
@@ -163,19 +180,23 @@ fn apply_safe_area_bottom_anchors(
 fn apply_safe_area_to_modal_scrims(
     insets: Res<SafeAreaInsets>,
     windows: Query<&Window>,
+    ui_scale: Option<Res<UiScale>>,
     mut scrims: Query<&mut Node, With<ModalScrim>>,
     new_scrims: Query<(), (With<ModalScrim>, Added<ModalScrim>)>,
 ) {
     let has_new = !new_scrims.is_empty();
-    if !insets.is_changed() && !has_new {
+    if !insets.is_changed() && !has_new && !ui_scale.as_ref().is_some_and(|s| s.is_changed()) {
         return;
     }
     let scale = windows.iter().next().map_or(1.0, |w| w.scale_factor());
     let window_height = windows.iter().next().map_or(800.0, |w| w.height());
     // Clamp each inset to 25% of screen height so an unexpectedly large OS
     // value can't push the modal card off the visible area entirely.
-    let top_logical = (insets.top / scale).min(window_height * 0.25);
+    // Physical insets are pre-divided by the UI scale — see
-    let bottom_logical = (insets.bottom / scale).min(window_height * 0.25);
+    // `apply_safe_area_anchors`.
+    let ui = effective_ui_scale(ui_scale.as_deref());
+    let top_logical = (insets.top / scale).min(window_height * 0.25) / ui;
+    let bottom_logical = (insets.bottom / scale).min(window_height * 0.25) / ui;
     for mut node in &mut scrims {
         // Set both edges so the scrim's content box equals the usable area
         // between the status bar and the gesture/navigation bar. With

solitaire_engine/src/settings_plugin/input.rs

@@ -363,6 +363,14 @@ pub(super) fn handle_settings_buttons(
                 changed.write(SettingsChangedEvent(settings.0.clone()));
                 // Text refreshed by `update_touch_input_mode_text` next frame.
             }
+            SettingsButton::CycleUiScale => {
+                settings.0.ui_scale = next_ui_scale(settings.0.ui_scale);
+                persist(&path, &settings.0);
+                changed.write(SettingsChangedEvent(settings.0.clone()));
+                // Text refreshed by `update_ui_scale_text`; the live
+                // `bevy::ui::UiScale` resource follows via
+                // `sync_ui_scale_resource` next frame.
+            }
             SettingsButton::ToggleWinnableDealsOnly => {
                 settings.0.winnable_deals_only = !settings.0.winnable_deals_only;
                 persist(&path, &settings.0);

solitaire_engine/src/settings_plugin/mod.rs

@@ -139,6 +139,10 @@ struct ReduceMotionText;
 #[derive(Component, Debug)]
 struct TouchInputModeText;
 
+/// Marks the `Text` node showing the current UI scale percentage.
+#[derive(Component, Debug)]
+struct UiScaleText;
+
 /// Marks the `Text` node showing the live tooltip-delay value.
 #[derive(Component, Debug)]
 struct TooltipDelayText;
@@ -277,6 +281,10 @@ enum SettingsButton {
     /// (auto-move on tap, default) and `TapToSelect` (first tap selects
     /// a card/stack, second tap on a target pile moves it).
     ToggleTouchInputMode,
+    /// Cycle [`Settings::ui_scale`] through 90 % → 100 % → 115 % →
+    /// 130 % → 90 %. Applied live via `bevy::ui::UiScale`; the table
+    /// stays window-fit (Phase K).
+    CycleUiScale,
     /// Toggle the [`Settings::winnable_deals_only`] flag. When on, new
     /// random Classic-mode deals are filtered through
     /// [`solitaire_core::game_state::GameState::solve_fresh_deal`] until one is provably
@@ -354,6 +362,7 @@ impl SettingsButton {
             SettingsButton::ToggleHighContrast => 61,
             SettingsButton::ToggleReduceMotion => 62,
             SettingsButton::ToggleTouchInputMode => 63,
+            SettingsButton::CycleUiScale => 64,
             // Picker rows — every swatch in a row shares the row's
             // priority so entity-index tiebreaking yields left → right.
             SettingsButton::SelectCardBack(_) => 70,
@@ -449,6 +458,11 @@ impl Plugin for SettingsPlugin {
                     handle_volume_keys,
                     record_window_geometry_changes,
                     persist_window_geometry_after_debounce,
+                    // State sync, not UI — runs even under `headless()`
+                    // so the live `bevy::ui::UiScale` always mirrors the
+                    // setting; rides the mutator spine so it is ordered
+                    // after every settings writer this frame.
+                    sync_ui_scale_resource,
                 )
                     .chain()
                     .in_set(SettingsMutation),
@@ -492,6 +506,7 @@ impl Plugin for SettingsPlugin {
                     update_high_contrast_backgrounds.run_if(resource_changed::<SettingsResource>),
                     update_reduce_motion_text,
                     update_touch_input_mode_text,
+                    update_ui_scale_text,
                     update_tooltip_delay_text,
                     update_time_bonus_multiplier_text,
                     update_replay_move_interval_text,

solitaire_engine/src/settings_plugin/tests.rs

@@ -736,3 +736,60 @@ fn scroll_clamps_offset_to_zero_at_top() {
         "scrolling past top must clamp to 0, got {offset}"
     );
 }
+
+// ---------------------------------------------------------------------------
+// Phase K: UI scale
+// ---------------------------------------------------------------------------
+
+#[test]
+fn ui_scale_steps_cycle_and_wrap() {
+    assert_eq!(next_ui_scale(0.9), 1.0);
+    assert_eq!(next_ui_scale(1.0), 1.15);
+    assert_eq!(next_ui_scale(1.15), 1.3);
+    assert_eq!(next_ui_scale(1.3), 0.9, "the cycle must wrap");
+    // A hand-edited in-between value advances to the next larger step.
+    assert_eq!(next_ui_scale(1.05), 1.15);
+}
+
+#[test]
+fn ui_scale_label_formats_as_percent() {
+    assert_eq!(ui_scale_label(0.9), "90%");
+    assert_eq!(ui_scale_label(1.0), "100%");
+    assert_eq!(ui_scale_label(1.15), "115%");
+    assert_eq!(ui_scale_label(1.3), "130%");
+}
+
+#[test]
+fn ui_scale_setting_syncs_the_bevy_resource() {
+    let mut app = headless_app();
+    app.insert_resource(UiScale(1.0));
+    app.world_mut()
+        .resource_mut::<SettingsResource>()
+        .0
+        .ui_scale = 1.3;
+    app.update();
+
+    assert!(
+        (app.world().resource::<UiScale>().0 - 1.3).abs() < f32::EPSILON,
+        "Settings::ui_scale must drive bevy::ui::UiScale"
+    );
+}
+
+#[test]
+fn ui_scale_out_of_range_sanitizes_on_load() {
+    use solitaire_data::settings::{UI_SCALE_MAX, UI_SCALE_MIN};
+
+    let wild = Settings {
+        ui_scale: 5.0,
+        ..Settings::default()
+    }
+    .sanitized();
+    assert_eq!(wild.ui_scale, UI_SCALE_MAX);
+
+    let tiny = Settings {
+        ui_scale: 0.1,
+        ..Settings::default()
+    }
+    .sanitized();
+    assert_eq!(tiny.ui_scale, UI_SCALE_MIN);
+}

solitaire_engine/src/settings_plugin/ui.rs

@@ -326,6 +326,15 @@ fn spawn_accessibility_tab(
         "One-tap: tap a card to auto-move it. Tap to select: first tap selects a card, second tap on a pile moves it.",
         font_res,
     );
+    toggle_row(
+        body,
+        "UI Scale",
+        UiScaleText,
+        ui_scale_label(settings.ui_scale),
+        SettingsButton::CycleUiScale,
+        "Scales all menus, buttons, and HUD text. The table itself always fits the screen.",
+        font_res,
+    );
     tooltip_delay_row(body, settings.tooltip_delay_secs, font_res);
 }
 

solitaire_engine/src/settings_plugin/updates.rs

@@ -515,6 +515,58 @@ pub(super) fn touch_input_mode_label(mode: &solitaire_data::settings::TouchInput
     }
 }
 
+/// The four UI-scale steps the settings row cycles through (Phase K).
+pub(super) const UI_SCALE_STEPS: [f32; 4] = [0.9, 1.0, 1.15, 1.3];
+
+/// The next UI-scale step after `current`, wrapping 130 % → 90 %. A
+/// hand-edited value between steps advances to the first step larger
+/// than it, so the cycle always makes visible progress.
+pub(super) fn next_ui_scale(current: f32) -> f32 {
+    for step in UI_SCALE_STEPS {
+        if step > current + 0.001 {
+            return step;
+        }
+    }
+    UI_SCALE_STEPS[0]
+}
+
+/// Display string for the UI-scale row, e.g. `"115%"`.
+pub(super) fn ui_scale_label(scale: f32) -> String {
+    format!("{:.0}%", scale * 100.0)
+}
+
+/// Refreshes the live UI-scale value text whenever settings change.
+pub(super) fn update_ui_scale_text(
+    settings: Res<SettingsResource>,
+    mut text_nodes: Query<&mut Text, With<UiScaleText>>,
+) {
+    if !settings.is_changed() {
+        return;
+    }
+    for mut text in &mut text_nodes {
+        **text = ui_scale_label(settings.0.ui_scale);
+    }
+}
+
+/// Applies `Settings::ui_scale` to the live [`bevy::ui::UiScale`]
+/// resource — at startup (first change tick) and whenever the setting
+/// changes. Absent under `MinimalPlugins` (no `bevy_ui`), hence the
+/// `Option`; the table is unaffected either way (`compute_layout`
+/// owns world-space sizing, not UI scale).
+pub(super) fn sync_ui_scale_resource(
+    settings: Res<SettingsResource>,
+    ui_scale: Option<ResMut<UiScale>>,
+) {
+    let Some(mut ui_scale) = ui_scale else { return };
+    if !settings.is_changed() {
+        return;
+    }
+    let target = settings.0.ui_scale;
+    if (ui_scale.0 - target).abs() > f32::EPSILON {
+        ui_scale.0 = target;
+    }
+}
+
 /// Display string for the "Smart window size" toggle. The argument
 /// is the *enabled* state (i.e. the inverse of the underlying
 /// `disable_smart_default_size` field) so reading the label gives