Navigation: choose the orbit centre: view centre, origin or point under the cursor (#1377)

Preferences ▸ Navigation ▸ Orbit around now offers View centre (the default, as before), Origin and Point under the cursor. A saved orbit_cursor preference migrates to the cursor option, and the control channel still accepts the old key.

Thanks to @kuraneko1 for this.

Co-authored-by: kuraneko1 <98832587+kuraneko1@users.noreply.github.com>

crates/ui-egui/src/viewport.rs

@@ -2304,16 +2304,22 @@ pub fn show(app: &mut SolveApp, ui: &mut egui::Ui) {
     if let Some((mode, delta)) = motion {
         if delta != egui::Vec2::ZERO {
             let mut params = json!({"motion":if mode == NavMode::Pan {"pan"} else {"orbit"},"delta":[delta.x,delta.y]});
-            if mode == NavMode::Orbit && app.preferences.orbit_cursor {
-                let pivot = match app.viewport.orbit_pivot {
-                    Some(pivot) => pivot,
-                    None => {
-                        let pivot = crate::prefs::pivot_under(app, &projection(app, rect), hover.unwrap_or(rect.center()) - delta);
-                        app.viewport.orbit_pivot = Some(pivot);
-                        pivot
-                    }
+            if mode == NavMode::Orbit {
+                let pivot = match app.preferences.orbit_around {
+                    crate::prefs::OrbitAround::ViewCentre => None,
+                    crate::prefs::OrbitAround::Origin => Some(Vec3::ZERO),
+                    crate::prefs::OrbitAround::Cursor => Some(match app.viewport.orbit_pivot {
+                        Some(pivot) => pivot,
+                        None => {
+                            let pivot = crate::prefs::pivot_under(app, &projection(app, rect), hover.unwrap_or(rect.center()) - delta);
+                            app.viewport.orbit_pivot = Some(pivot);
+                            pivot
+                        }
+                    }),
                 };
-                params["pivot"] = json!(pivot);
+                if let Some(pivot) = pivot {
+                    params["pivot"] = json!(pivot);
+                }
             }
             camera_motion(app, rect, params);
         }
@@ -3345,7 +3351,17 @@ fn orbit_drag(app: &mut SolveApp, rect: Rect, dx: f64, dy: f64, press: Option<Po
                 target.pitch = previous.target.pitch;
             }
         }
-        let pivot = app.viewport.orbit_pivot.filter(|_| around_cursor).and_then(|p| {
+        // The cursor and origin pivots stay still while a snap eases in; the axis gizmo has no
+        // pivot (it orbits about the view centre, see `axis_view`).
+        let pivot = if around_cursor {
+            match app.preferences.orbit_around {
+                crate::prefs::OrbitAround::Origin => Some(Vec3::ZERO),
+                _ => app.viewport.orbit_pivot,
+            }
+        } else {
+            None
+        }
+        .and_then(|p| {
             app.cam = displayed;
             projection(app, rect).to_screen(p).map(|at| (p, at))
         });
@@ -4429,7 +4445,7 @@ mod tests {
         let ctx = egui::Context::default();
         let mut app = hover_app(false);
         app.preferences.nav = "touchpad".into();
-        app.preferences.orbit_cursor = true;
+        app.preferences.orbit_around = crate::prefs::OrbitAround::Cursor;
         let p = pos2(350.0, 300.0);
         let alt = egui::Modifiers { alt: true, ..Default::default() };
         hover_frame(&mut app, &ctx, vec![egui::Event::PointerMoved(p)]);
@@ -5499,10 +5515,35 @@ mod tests {
         }
     }
 
+    /// The origin pivot holds through a Shift drag that snaps to an axis: the spring eases the
+    /// view round without letting the origin slide on screen.
+    #[test]
+    fn snapping_keeps_the_origin_still() {
+        let mut h = crate::scenario::Harness::new();
+        h.app.preferences.orbit_around = crate::prefs::OrbitAround::Origin;
+        h.app.run("solid.box", json!({"length":40,"width":40,"height":40})).unwrap();
+        h.app.fit_view();
+        let rect = h.app.viewport.rect.unwrap();
+        let at = rect.center() + vec2(50.0, -20.0);
+        orbit_drag(&mut h.app, rect, 0.0, 0.0, Some(at), true, true);
+        assert_eq!(
+            h.app.viewport.orbit_snap.as_ref().and_then(|s| s.pivot).map(|(p, _)| p),
+            Some(Vec3::ZERO),
+            "the origin is the pivot while snapping"
+        );
+        let before = projection(&h.app, rect).to_screen(Vec3::ZERO).unwrap();
+        for _ in 0..30 {
+            orbit_drag(&mut h.app, rect, 4.0, 2.0, Some(at), true, true);
+            step_orbit_snap(&mut h.app, rect, 1.0 / 60.0);
+            let after = projection(&h.app, rect).to_screen(Vec3::ZERO).unwrap();
+            assert!(after.distance(before) < 2.0, "{before:?} -> {after:?}");
+        }
+    }
+
     #[test]
     fn shift_orbit_keeps_cursor_pivot_and_default_middle_pan() {
         let mut h = crate::scenario::Harness::new();
-        h.app.preferences.orbit_cursor = true;
+        h.app.preferences.orbit_around = crate::prefs::OrbitAround::Cursor;
         h.app.run("solid.box", json!({"length":40,"width":40,"height":40})).unwrap();
         h.app.fit_view();
         let rect = h.app.viewport.rect.unwrap();