Preferences: reverse horizontal pan direction (#2007) (#2047)

Thanks @lasselian.

crates/ui-egui/src/navigation.rs

@@ -307,7 +307,8 @@ pub(crate) fn handle(app: &mut SolveApp, ui: &mut egui::Ui, rect: Rect, resp: &e
         // (its End was lost); a stuck flag would pan future mouse input.
         app.viewport.trackpad_gesture = false;
     }
-    let pan = if trackpad_pan { raw.pan } else { egui::Vec2::ZERO } + raw.mouse_pan;
+    let mut pan = if trackpad_pan { raw.pan } else { egui::Vec2::ZERO } + raw.mouse_pan;
+    pan.x *= crate::prefs::pan_sign_x(app);
     let scroll = if app.viewport.wheel_zoom_raw_until_idle || (trackpad_pan && app.viewport.trackpad_until_idle) {
         raw.zoom + if trackpad_pan { 0.0 } else { raw.point_zoom }
     } else {

crates/ui-egui/src/prefs.rs

@@ -321,6 +321,8 @@ pub struct Prefs {
     pub smooth_wheel_zoom: bool,
     /// Two-finger trackpad scroll pans (off: it zooms like the wheel); pinch always zooms.
     pub trackpad_pan: bool,
+    /// Horizontal trackpad and thumb-wheel scrolling pans the view the other way (#2007).
+    pub pan_reverse_x: bool,
     /// View changes (axis view, Look At, Home) animate; `look_at_speed` scales how fast.
     pub look_at_anim: bool,
     pub look_at_speed: f32,
@@ -432,6 +434,7 @@ impl Default for Prefs {
             zoom_to_cursor: true,
             smooth_wheel_zoom: true,
             trackpad_pan: true,
+            pan_reverse_x: false,
             look_at_anim: true,
             look_at_speed: 1.0,
             up_axis: "z".into(),
@@ -626,6 +629,7 @@ fn defaults(app: &mut SolveApp, page: usize) {
             p.zoom_to_cursor = d.zoom_to_cursor;
             p.smooth_wheel_zoom = d.smooth_wheel_zoom;
             p.trackpad_pan = d.trackpad_pan;
+            p.pan_reverse_x = d.pan_reverse_x;
             p.orbit_around = d.orbit_around;
             p.orbit_cursor = d.orbit_cursor;
             p.space_mouse_enabled = d.space_mouse_enabled;
@@ -729,6 +733,11 @@ pub fn nav_mode(app: &SolveApp, button: NavButton, mods: Modifiers) -> Option<Na
     nav_preset(&app.preferences.nav).mode(button, mods)
 }
 
+/// +1, or −1 when horizontal scrolling pans the other way (#2007).
+pub fn pan_sign_x(app: &SolveApp) -> f32 {
+    if app.preferences.pan_reverse_x { -1.0 } else { 1.0 }
+}
+
 /// +1, or −1 when the wheel zooms the other way.
 pub fn zoom_sign(app: &SolveApp) -> f64 {
     if app.preferences.zoom_reverse { -1.0 } else { 1.0 }
@@ -1158,6 +1167,10 @@ fn page(app: &mut SolveApp, ui: &mut egui::Ui, t: &Tokens) {
                 crate::i18n::tr_label("Trackpad gestures pan (off: they zoom like the wheel); mouse wheel zooms, thumb wheel pans sideways, pinch always zooms")
             });
             ui.end_row();
+            ui.label(crate::i18n::tr_label("Reverse horizontal pan direction"));
+            ui.checkbox(&mut app.preferences.pan_reverse_x, "")
+                .on_hover_text(crate::i18n::tr_label("Horizontal two-finger scrolling and the thumb wheel pan the other way"));
+            ui.end_row();
             ui.label(crate::i18n::tr_label("Orbit around"));
             // Wrapped: three choices, and German or Russian labels are long.
             ui.horizontal_wrapped(|ui| {
@@ -1838,6 +1851,18 @@ mod tests {
         assert_eq!(other.preferences.nav, OPENSCAD_NAV);
     }
 
+    #[test]
+    fn pan_reverse_x_defaults_off_persists_and_flips_the_sign() {
+        assert!(!serde_json::from_value::<Prefs>(json!({})).unwrap().pan_reverse_x);
+        let mut app = SolveApp::new(solidcraft_engine::Session::default(), Default::default());
+        assert_eq!(pan_sign_x(&app), 1.0);
+        set(&mut app, &json!({"pan_reverse_x": true})).unwrap();
+        assert_eq!(pan_sign_x(&app), -1.0);
+        let mut other = SolveApp::new(solidcraft_engine::Session::default(), Default::default());
+        other.load_prefs(&app.prefs());
+        assert!(other.preferences.pan_reverse_x);
+    }
+
     #[test]
     fn trackpad_pan_defaults_on_persists_and_follows_dialog_buttons() {
         assert!(serde_json::from_value::<Prefs>(json!({})).unwrap().trackpad_pan);