navigation: selectable mouse navigation style

Options → User Preferences → Navigation style picks which mouse
gestures pan and orbit the model view (#1480):

- CAD (default): middle button pans, Shift + middle button orbits.
- Blender: middle button orbits, Shift + middle button pans.
- CATIA: middle button pans; pressing the left button during it orbits,
  so 3D navigation needs only the mouse.

An armed orbit tool always orbits. The choice is saved with the user
settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/update/file.rs

@@ -778,6 +778,7 @@ impl OpenCADStudio {
             polar: self.polar_mode,
             polar_increment_deg: self.polar_increment_deg,
             zoom_wheel_reversed: self.zoom_wheel_reversed,
+            navigation_style: self.navigation_style,
             touchpad_pan: self.touchpad_pan,
             ui_scale_percent: self.ui_scale_percent,
             zoom_factor: self.zoom_factor,
@@ -913,6 +914,7 @@ impl OpenCADStudio {
         self.polar_mode = s.polar;
         self.polar_increment_deg = s.polar_increment_deg;
         self.zoom_wheel_reversed = s.zoom_wheel_reversed;
+        self.navigation_style = s.navigation_style;
         self.touchpad_pan = s.touchpad_pan;
         self.ui_scale_percent = crate::app::settings::clamp_ui_scale(s.ui_scale_percent);
         self.zoom_factor = crate::app::settings::clamp_zoom_factor(s.zoom_factor);

src/app/update/mod.rs

@@ -4482,6 +4482,25 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            // CATIA navigation: the left button pressed during a middle drag
+            // turns the drag into an orbit instead of starting a pick.
+            Message::ViewportLeftPressAt(_) | Message::ViewportLeftPress | Message::PanePress(_)
+                if self.navigation_style == crate::app::settings::NavigationStyle::Catia
+                    && self.tabs[self.active_tab]
+                        .scene
+                        .selection
+                        .borrow()
+                        .input
+                        .middle_down =>
+            {
+                self.nav_left_with_middle = true;
+                Task::none()
+            }
+            Message::ViewportLeftRelease | Message::PaneRelease(_) if self.nav_left_with_middle => {
+                self.nav_left_with_middle = false;
+                Task::none()
+            }
+
             Message::ViewportMove(p) => self.on_viewport_move(p),
 
             Message::ViewportExit => self.on_viewport_exit(),
@@ -4686,6 +4705,7 @@ impl OpenCADStudio {
             }
 
             Message::ViewportMiddleRelease => {
+                self.nav_left_with_middle = false;
                 let i = self.active_tab;
                 let mut sel = self.tabs[i].scene.selection.borrow_mut();
                 sel.input.middle_down = false;
@@ -9225,6 +9245,12 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::NavigationStyleChanged(style) => {
+                self.navigation_style = style;
+                self.persist_settings_if_changed();
+                Task::none()
+            }
+
             Message::MenuBarChanged(shown) => {
                 self.show_menu_bar = shown;
                 self.persist_settings_if_changed();

src/app/update/viewport.rs

@@ -1416,7 +1416,7 @@ impl OpenCADStudio {
                 // — the requested Zoom=wheel / Pan=MMB / Rotate=Shift+MMB
                 // scheme (#229). Floating viewports and paper keep the
                 // plain MMB pan.
-                if self.shift_down || self.tabs[i].orbit_mode {
+                if self.middle_drag_orbits(i) {
                     if self.tabs[i].scene.active_viewport.is_some() {
                         // Orbit the floating viewport's own model view.
                         drop(sel);
@@ -3165,6 +3165,18 @@ impl OpenCADStudio {
         Task::none()
     }
 
+    /// Whether a middle-button drag orbits rather than pans, by the
+    /// navigation style (an armed orbit tool always orbits).
+    fn middle_drag_orbits(&self, i: usize) -> bool {
+        use crate::app::settings::NavigationStyle;
+        self.tabs[i].orbit_mode
+            || match self.navigation_style {
+                NavigationStyle::Cad => self.shift_down,
+                NavigationStyle::Blender => !self.shift_down,
+                NavigationStyle::Catia => self.nav_left_with_middle,
+            }
+    }
+
     pub(crate) fn on_viewport_exit(&mut self) -> Task<Message> {
         let i = self.active_tab;
         self.tabs[i].measurement.live_visible = false;