fix(ui): restore free Shift-middle orbit

crates/ui-egui/src/viewport.rs

@@ -1534,7 +1534,11 @@ pub fn show(app: &mut SolveApp, ui: &mut egui::Ui) {
     if mode == Some(NavMode::Orbit) {
         let press = ui.input(|i| i.pointer.press_origin());
         app.cancel_view_animation();
-        orbit_drag(app, rect, f64::from(delta.x), f64::from(delta.y), press, mods.shift, true);
+        // Shift can be required to enter orbit (Fusion/Inventor middle drag), rather
+        // than an additional request for snapping. Only an extra modifier snaps.
+        let without_shift = egui::Modifiers { shift: false, ..mods };
+        let snap = mods.shift && (!middle || crate::prefs::nav_mode(app, middle, secondary_down, without_shift) == Some(NavMode::Orbit));
+        orbit_drag(app, rect, f64::from(delta.x), f64::from(delta.y), press, snap, true);
     } else {
         if matches!(mode, Some(NavMode::Pan | NavMode::Zoom)) {
             app.viewport.orbit_snap = None;
@@ -3408,7 +3412,8 @@ mod tests {
         h.call("ui.view", json!({"view":"front"}));
         let before = h.app.cam;
         h.call("ui.drag", json!({"x0":800,"y0":500,"x1":1020,"y1":500,"button":"middle","shift":true,"steps":40}));
-        assert!((h.app.cam.yaw - std::f64::consts::FRAC_PI_2).abs() < 1e-6, "before={before:?}, after={:?}", h.app.cam);
+        assert!((h.app.cam.yaw - 1.76).abs() < 1e-6, "before={before:?}, after={:?}", h.app.cam);
+        assert!(h.app.viewport.orbit_snap.is_none());
         h.call("ui.view", json!({"view":"front"}));
         h.call("ui.drag", json!({"x0":800,"y0":500,"x1":850,"y1":520,"button":"middle"}));
         assert_eq!(h.app.cam.yaw, before.yaw);
@@ -3416,6 +3421,27 @@ mod tests {
         assert_ne!(h.app.cam.target, before.target);
     }
 
+    #[test]
+    fn preset_shift_middle_orbit_is_free_but_shift_right_orbit_snaps() {
+        for preset in ["fusion", "inventor"] {
+            let mut h = crate::scenario::Harness::new();
+            h.app.preferences.nav = preset.into();
+            h.call("ui.view", json!({"view":"front"}));
+            let before = h.app.cam;
+            h.call("ui.drag", json!({"x0":800,"y0":500,"x1":850,"y1":520,"button":"middle","shift":true,"steps":20}));
+            let mut expected = before;
+            expected.orbit(50.0, 20.0);
+            assert!((h.app.cam.yaw - expected.yaw).abs() < 1e-6, "{preset}: {:?}", h.app.cam);
+            assert!((h.app.cam.pitch - expected.pitch).abs() < 1e-6, "{preset}: {:?}", h.app.cam);
+            assert_eq!(h.app.cam.target, before.target);
+            assert_eq!(h.app.cam.distance, before.distance);
+            assert!(h.app.viewport.orbit_snap.is_none());
+            h.call("ui.view", json!({"view":"front"}));
+            h.call("ui.drag", json!({"x0":800,"y0":500,"x1":1020,"y1":500,"button":"right","shift":true,"steps":40}));
+            assert!((h.app.cam.yaw - std::f64::consts::FRAC_PI_2).abs() < 1e-6, "{preset}: {:?}", h.app.cam);
+        }
+    }
+
     #[test]
     fn axis_view_click_again_flips_and_drag_snaps() {
         let mut h = crate::scenario::Harness::new();

docs/book/src/guide/ui-tour.md

@@ -14,8 +14,9 @@
   row gives that item's menu. Rows drag into groups and other components.
 - **Viewport.** Click to select, Shift or Ctrl to add, drag for a window or crossing box. The
   wheel zooms at the cursor, the middle button pans and right-drag orbits freely (the mouse
-  preset in Preferences switches to SolidWorks or Inventor style). Hold Shift during an orbit
+  preset in Preferences switches to SolidWorks or Inventor style). Shift+middle orbits freely
-  to snap to the nearest standard or diagonal view; the default Shift+middle gesture also snaps.
+  in the default and Inventor presets. Shift+right-drag snaps to the nearest standard or
+  diagonal view; Shift does not request snapping when the preset already requires it to orbit.
   The axis view shows the world's X/Y/Z directions in SolidCraft's colors. Click a signed
   axis tip to look along that axis; click the aligned tip again to look from the opposite side.
   Drag the axis view to orbit around the view centre, with Shift for snapping. Top and bottom