fix(ui): respect native desktop scale under Auto UI scaling (#1278) (#3165)

* fix(ui): respect native desktop scale under Auto UI scaling (#1278)

* UI scale: drop the now-unused monitor size, update docs and scorecard

Merge main; Auto no longer reads the monitor size, so remove the parameter and its
computation, simplify the test, and update ui-design.md and UI-217-9 to match.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

---------

Co-authored-by: Brandon Thomas <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

crates/ui-egui/src/prefs_ui.rs

@@ -341,30 +341,20 @@ fn presets_store(app: &mut PhotocraftApp) {
 
 /// Resolve an absolute pixels-per-point preference without multiplying the OS DPI twice.
 /// Monitor dimensions are physical pixels, independent of window size and UI zoom.
-fn display_scale(pref: prefs::UiScale, native: Option<f32>, monitor_px: Option<egui::Vec2>) -> f32 {
+fn display_scale(pref: prefs::UiScale, native: Option<f32>) -> f32 {
     let native = native.filter(|v| v.is_finite() && *v > 0.0).unwrap_or(1.0);
     match pref {
-        prefs::UiScale::Auto => {
-            // Follow the system's scale, fractional ones included (125%, 150%, 175%: #1072).
-            // Only when the system reports no scaling at all (100%) does a 4K display fall back
-            // to 200%, since unscaled 4K controls are unreadably small (#225). Overriding a scale
-            // the user picked in their desktop settings left only "too small" or "too big".
-            let unscaled = (native - 1.0).abs() < 0.01;
-            let is_4k = monitor_px.is_some_and(|s| s.x.is_finite() && s.y.is_finite() && s.x.min(s.y) >= 2160.0 && s.x.max(s.y) >= 3840.0);
-            if unscaled && is_4k { 2.0 } else { native }
-        }
+        // The system's scale, fractional ones included (125%, 150%, 175%: #1072), and 100% on a
+        // large 4K display run unscaled (#1278); 200% there is a fixed choice.
+        prefs::UiScale::Auto => native,
         fixed => fixed.name().parse::<f32>().map_or(1.0, |pct| pct / 100.0),
     }
 }
 
 fn sync_display_scale(app: &PhotocraftApp, ctx: &egui::Context) {
     let native = ctx.native_pixels_per_point();
-    // ViewportInfo uses egui points, including the current UI zoom. Converting back to
-    // physical pixels avoids oscillating between 100% and 200% on successive frames.
-    // logic() can receive new viewport DPI before InputState::pixels_per_point updates.
     let native_scale = native.filter(|v| v.is_finite() && *v > 0.0).unwrap_or(1.0);
-    let monitor_px = ctx.input(|i| i.viewport().monitor_size).map(|s| s * (native_scale * ctx.zoom_factor()));
-    let scale = display_scale(app.session.prefs().interface.ui_scale, native, monitor_px);
+    let scale = display_scale(app.session.prefs().interface.ui_scale, native);
     ctx.set_zoom_factor(scale / native_scale);
 }
 
@@ -2463,28 +2453,16 @@ mod tests {
     }
 
     #[test]
-    fn auto_scale_detects_4k_and_preserves_system_scale() {
+    fn auto_scale_preserves_system_scale() {
         use prefs::UiScale::Auto;
-        for size in [vec2(3840.0, 2160.0), vec2(4096.0, 2160.0), vec2(2160.0, 3840.0)] {
-            assert_eq!(display_scale(Auto, Some(1.0), Some(size)), 2.0);
-            // A fractional system scale is the user's choice and is kept as is (#1072).
-            for dpi in [1.25, 1.5, 1.75, 2.0, 2.5] {
-                assert_eq!(display_scale(Auto, Some(dpi), Some(size)), dpi);
-            }
+        // Whatever the monitor, 4K included: an unscaled desktop stays at 100% (#1278), and a
+        // fractional or below-100% system scale is the user's choice (#1072).
+        for dpi in [0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5, 3.0] {
+            assert_eq!(display_scale(Auto, Some(dpi)), dpi);
         }
-        // Below 100% is a system choice too, even on 4K.
-        assert_eq!(display_scale(Auto, Some(0.75), Some(vec2(3840.0, 2160.0))), 0.75);
-        for size in [vec2(1920.0, 1080.0), vec2(2560.0, 1440.0)] {
-            for dpi in [1.25, 1.5, 1.75] {
-                assert_eq!(display_scale(Auto, Some(dpi), Some(size)), dpi);
-            }
-        }
-        assert_eq!(display_scale(Auto, Some(3.0), Some(vec2(3840.0, 2160.0))), 3.0);
-        for size in [vec2(1920.0, 1080.0), vec2(2560.0, 1440.0), vec2(3840.0, 1080.0)] {
-            assert_eq!(display_scale(Auto, Some(1.0), Some(size)), 1.0);
-        }
-        assert_eq!(display_scale(Auto, None, None), 1.0);
-        assert_eq!(display_scale(Auto, Some(f32::NAN), Some(vec2(f32::INFINITY, 2160.0))), 1.0);
+        assert_eq!(display_scale(Auto, None), 1.0);
+        assert_eq!(display_scale(Auto, Some(f32::NAN)), 1.0);
+        assert_eq!(display_scale(Auto, Some(-2.0)), 1.0);
     }
 
     #[test]
@@ -2507,13 +2485,13 @@ mod tests {
                 assert!((ctx.pixels_per_point() - expected).abs() < 1e-4);
             };
             for _ in 0..4 {
-                step(vec2(3840.0, 2160.0), 1.0, 2.0);
+                step(vec2(3840.0, 2160.0), 1.0, 1.0);
             }
             step(vec2(1920.0, 1080.0), 1.0, 1.0);
             step(vec2(3840.0, 2160.0), 1.5, 1.5);
             step(vec2(3840.0, 2160.0), 1.25, 1.25);
             step(vec2(2560.0, 1440.0), 1.75, 1.75);
-            step(vec2(3840.0, 2160.0), 1.0, 2.0);
+            step(vec2(3840.0, 2160.0), 1.0, 1.0);
         }
         for (pref, expected) in [("200", 2.0), ("125", 1.25), ("150", 1.5), ("100", 1.0), ("95", 0.95), ("90", 0.9), ("85", 0.85), ("80", 0.8), ("auto", 1.5)] {
             app.run("prefs.set", json!({"values": {"interface.uiScale": pref}})).unwrap();

docs/scorecard.md

@@ -190,7 +190,7 @@ Unread: `general.color_picker`, `general.animated_zoom`, `general.zoom_resizes_w
 | UI-217-6 | Document tabs: overflow list, context menu (Close/Others/All/Reveal), drag to reorder | done | [#217](https://github.com/storytold/photocraft/issues/217) | canvas.rs: Close/Others/All menu with unsaved prompt; Reveal reuses file.revealInFinder (engine layer_menu_cmds::reveal); the » chevron (tab_strip) lists overflow; dragging a tab reorders via document.move |
 | UI-217-7 | Command palette shows recently run commands on an empty query | done | [#217](https://github.com/storytold/photocraft/issues/217) | palette.rs: note_recent from menus::invoke keeps the last 8 commands (dedup, newest first); an empty query lists them via recent_hits; the_palette_records_and_replays_recent_commands_on_an_empty_query covers record -> empty query -> replay |
 | UI-217-8 | Tool-specific canvas right-click menu; right-click spelling suggestions in text fields | partial | [#217](https://github.com/storytold/photocraft/issues/217) | paint_mouse.rs brush picker and canvas_tool_menu.rs selection actions; text_field_menu.rs gives every text field its right-click Undo/Cut/Copy/Paste/Delete/Select All menu (#2921); other tools missing; spelling suggestions (edit.checkSpelling suggest) not in the text-field menu yet |
-| UI-217-9 | UI scale presets 100/115/125/150/200 % through zoom_factor, remembered | done | [#217](https://github.com/storytold/photocraft/issues/217) | prefs::UiScale offers Auto plus 75 to 300 percent (13 presets, more than the five this row lists); prefs_ui.rs display_scale resolves it (Auto follows the system scale and only jumps to 200 percent on an unscaled 4K display, #1072/#225) and sync_display_scale applies it with ctx.set_zoom_factor. It is a preference, so it is remembered. The zoom_factor assert in input_tests.rs is about canvas zoom not scaling the interface, not about this setting |
+| UI-217-9 | UI scale presets 100/115/125/150/200 % through zoom_factor, remembered | done | [#217](https://github.com/storytold/photocraft/issues/217) | prefs::UiScale offers Auto plus 75 to 300 percent (13 presets, more than the five this row lists); prefs_ui.rs display_scale resolves it (Auto follows the system scale, fractional and unscaled 4K included, #1072/#1278) and sync_display_scale applies it with ctx.set_zoom_factor. It is a preference, so it is remembered. The zoom_factor assert in input_tests.rs is about canvas zoom not scaling the interface, not about this setting |
 | UI-217-10 | Appearance: animation toggle, canvas pattern toggle per theme, start-screen recents | missing | [#217](https://github.com/storytold/photocraft/issues/217) | No such prefs; start screen (canvas.rs:825) has no recents |
 | UI-217-11 | Soft dark and soft light themes with picker previews; outlined knobs in light themes | missing | [#217](https://github.com/storytold/photocraft/issues/217) | theme.rs ThemeKind has twelve themes (the four Pro brightness levels, Studio and Studio Light, Classic, Adwaita and Adwaita Dark, Solarized Dark, Breeze Light and Breeze Dark); no Soft dark or Soft light, and no outlined knobs in the light themes |
 | UI-217-12 | Save custom New Document presets; a real Recent category | partial | [#217](https://github.com/storytold/photocraft/issues/217) | document_preset_cmds.rs and new_doc_ui.rs: named presets save/select/delete through preferences; Recent remains a static list plus Clipboard |

docs/ui-design.md

@@ -164,11 +164,9 @@ change the current window's decorations; the next launch reads the saved choice.
 
 Edit → Preferences → Interface → UI Scale applies immediately. Auto follows the operating
 system's display scale, including fractional scales such as 125%, 150% and 175% (on Linux,
-Wayland's fractional scale or X11's `Xft.dpi`). Only when the system reports no scaling (100%) on
-a 4K or larger monitor does Auto use 200%, so text and controls remain readable. Detection uses the current monitor,
-including portrait displays, and updates when the window moves between monitors. If monitor
-size is unavailable, Auto follows system DPI. The fixed choices (75% to 300%) set an absolute UI
-scale, allowing large 4K displays to use smaller controls when desired. Canvas zoom shortcuts
+Wayland's fractional scale or X11's `Xft.dpi`), and updates when the window moves between
+monitors. A 4K display the system runs at 100% stays at 100% (#1278). The fixed choices (75% to
+300%) set an absolute UI scale, for example 200% on an unscaled 4K display. Canvas zoom shortcuts
 continue to control the document independently of UI scaling.
 
 Interface → UI Font Size changes interface text independently of UI Scale and canvas zoom.

scorecard/ui.toml

@@ -66,7 +66,7 @@ id = "UI-217-9"
 target = "UI scale presets 100/115/125/150/200 % through zoom_factor, remembered"
 status = "done"
 issue = 217
-note = "prefs::UiScale offers Auto plus 75 to 300 percent (13 presets, more than the five this row lists); prefs_ui.rs display_scale resolves it (Auto follows the system scale and only jumps to 200 percent on an unscaled 4K display, #1072/#225) and sync_display_scale applies it with ctx.set_zoom_factor. It is a preference, so it is remembered. The zoom_factor assert in input_tests.rs is about canvas zoom not scaling the interface, not about this setting"
+note = "prefs::UiScale offers Auto plus 75 to 300 percent (13 presets, more than the five this row lists); prefs_ui.rs display_scale resolves it (Auto follows the system scale, fractional and unscaled 4K included, #1072/#1278) and sync_display_scale applies it with ctx.set_zoom_factor. It is a preference, so it is remembered. The zoom_factor assert in input_tests.rs is about canvas zoom not scaling the interface, not about this setting"
 
 [[item]]
 id = "UI-217-10"