feat(nav): turntable orbit, selection/cursor pivot, Shift+MMB rotate (#229)

Rework 3D view navigation:

- Turntable / lock-horizon orbit: horizontal drag yaws about world +Z,
  vertical drag pitches about the horizontal camera-right axis, so the
  view never banks. Pitch is pole-clamped but the straight-down default
  view can still be tilted out of.
- Orbit centre: the selection's centre when something is selected,
  otherwise the point under the cursor — no longer only the file centre.
  The camera revolves rigidly about the pivot, so it stays put on screen
  and the view doesn't jump.
- Mouse scheme: Zoom = wheel, Pan = MMB, Rotate = Shift+MMB. Right-drag
  no longer orbits (right-click stays context menu / Enter). Floating
  viewports orbit with Shift+MMB too.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update/mod.rs

@@ -1215,6 +1215,7 @@ impl OpenCADStudio {
                 sel.right_press_time = None;
                 sel.right_last_pos = None;
                 sel.right_dragging = false;
+                sel.orbit_pivot = None;
                 if !was_click {
                     return Task::none();
                 }
@@ -1257,6 +1258,9 @@ impl OpenCADStudio {
                 let mut sel = self.tabs[i].scene.selection.borrow_mut();
                 sel.middle_down = false;
                 sel.middle_last_pos = None;
+                // End of a Shift+MMB orbit — drop the captured pivot so the next
+                // gesture recomputes it against the current selection. (#229)
+                sel.orbit_pivot = None;
                 Task::none()
             }
 

src/app/update/viewport.rs

@@ -20,10 +20,6 @@ use acadrust::{EntityType as AcadEntityType, Handle};
 use iced::time::Instant;
 use iced::{mouse, Point, Task};
 
-/// How long the right button must be held (ms) before a right-drag is treated
-/// as an orbit. A press + release inside this window stays a click (context
-/// menu / Enter), so quick right-clicks aren't lost to slight pointer jitter.
-const RIGHT_HOLD_MS: u128 = 150;
 /// Pixel radius for grabbing a UCS-icon grip (origin dot or an axis tip).
 const UCS_GRIP_HIT_PX: f32 = 9.0;
 /// Pixel reach for hovering/clicking the icon body (origin, tips, or an arm).
@@ -571,72 +567,44 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                     }
                 }
 
-                if sel.right_down {
-                    // Time-based click-vs-orbit split: a quick right-click
-                    // (press + release within RIGHT_HOLD_MS) is always a click —
-                    // it opens the context menu / fires Enter on release, even if
-                    // the pointer drifted a little. Orbit only engages once the
-                    // button has been *held* past the threshold and the pointer
-                    // is actually moving, so hand jitter during a click never
-                    // promotes it to an orbit drag.
-                    if !sel.right_dragging {
-                        let held = sel
-                            .right_press_time
-                            .map(|t| t.elapsed().as_millis() >= RIGHT_HOLD_MS)
-                            .unwrap_or(false);
-                        let moved = sel
-                            .right_press_pos
-                            .map(|press| {
-                                let (dx, dy) = (p.x - press.x, p.y - press.y);
-                                dx * dx + dy * dy > 4.0
-                            })
-                            .unwrap_or(false);
-                        if held && moved {
-                            sel.right_dragging = true;
-                            sel.context_menu = None;
-                            // An orbit restarts the right-click cycle.
-                            sel.right_click_entered = false;
-                            // Start the orbit from the current position so the
-                            // view doesn't jump by the pre-threshold movement.
-                            sel.right_last_pos = Some(p);
-                        }
-                    }
-                    if sel.right_dragging {
-                        if let Some(last) = sel.right_last_pos {
-                            let (dx, dy) = (p.x - last.x, p.y - last.y);
-                            if self.tabs[i].scene.active_viewport.is_some() {
-                                // Update position before dropping the borrow.
-                                sel.right_last_pos = Some(p);
-                                drop(sel);
-                                self.tabs[i].scene.orbit_active_viewport(dx, dy);
-                                // Bump so the GPU re-uploads the viewport's
-                                // re-culled wire set after the view rotates.
-                                self.tabs[i].scene.camera_generation += 1;
-                                return Task::none();
-                            } else if self.tabs[i].scene.current_layout == "Model" {
-                                sel.right_last_pos = Some(p);
-                                drop(sel);
-                                self.tabs[i].scene.camera.borrow_mut().orbit(dx, dy);
-                                self.tabs[i].scene.camera_generation += 1;
-                                return Task::none();
-                            } else {
-                                // Paper sheet is top-locked: right-drag never
-                                // orbits it (orbiting would corrupt the camera
-                                // frame and skew subsequent pans).
-                                sel.right_last_pos = Some(p);
-                                return Task::none();
-                            }
-                        } else {
-                            sel.right_last_pos = Some(p);
-                        }
-                    }
-                }
-
                 let (mid_down, mid_last, vp_size) =
                     (sel.middle_down, sel.middle_last_pos, sel.vp_size);
                 if mid_down {
                     if let Some(last) = mid_last {
                         let (dx, dy) = (p.x - last.x, p.y - last.y);
+                        // Shift+MMB drag orbits the model view instead of panning
+                        // — the requested Zoom=wheel / Pan=MMB / Rotate=Shift+MMB
+                        // scheme (#229). Floating viewports and paper keep the
+                        // plain MMB pan.
+                        if self.shift_down {
+                            if self.tabs[i].scene.active_viewport.is_some() {
+                                // Orbit the floating viewport's own model view.
+                                drop(sel);
+                                self.tabs[i].scene.orbit_active_viewport(dx, dy);
+                                self.tabs[i].scene.camera_generation += 1;
+                                self.tabs[i].scene.selection.borrow_mut().middle_last_pos =
+                                    Some(p);
+                                return Task::none();
+                            } else if self.tabs[i].scene.current_layout == "Model" {
+                                if sel.orbit_pivot.is_none() {
+                                    // Selection centre when something is selected,
+                                    // otherwise the point under the cursor. (#229)
+                                    sel.orbit_pivot = self.tabs[i]
+                                        .scene
+                                        .orbit_pivot()
+                                        .or(Some(self.tabs[i].last_cursor_world.as_dvec3()));
+                                }
+                                let pivot = sel.orbit_pivot;
+                                drop(sel);
+                                self.tabs[i].scene.camera.borrow_mut().orbit(dx, dy, pivot);
+                                self.tabs[i].scene.camera_generation += 1;
+                                self.tabs[i].scene.selection.borrow_mut().middle_last_pos =
+                                    Some(p);
+                                return Task::none();
+                            }
+                            // Paper sheet is top-locked: Shift+MMB falls through
+                            // to the plain pan below.
+                        }
                         // Pan scale uses the active tile's size (ortho size
                         // is relative to viewport height), so a tiled pane
                         // pans at the correct rate.
@@ -1244,6 +1212,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                 sel.right_click_entered = false;
                 sel.middle_down = false;
                 sel.middle_last_pos = None;
+                sel.orbit_pivot = None;
                 sel.box_anchor = None;
                 sel.box_anchor_world = None;
                 sel.box_current = None;

src/scene/mod.rs

@@ -3370,6 +3370,42 @@ impl Scene {
         result
     }
 
+    /// The AABB centre of the current selection, in absolute world coordinates
+    /// (same space as `Camera::target`) — the point the 3D view orbits around
+    /// when something is selected. `None` when nothing is selected; the caller
+    /// then orbits about the point under the cursor. (#229)
+    pub fn orbit_pivot(&self) -> Option<glam::DVec3> {
+        if self.selected.is_empty() {
+            return None;
+        }
+        let block = self.current_layout_block_handle();
+        let wires = self.wires_for_block_culled(block, None, None, None, None);
+        let mut min = glam::DVec2::splat(f64::INFINITY);
+        let mut max = glam::DVec2::splat(f64::NEG_INFINITY);
+        let mut any = false;
+        for wire in &wires {
+            let Some(h) = Self::handle_from_wire_name(&wire.name) else {
+                continue;
+            };
+            if !self.selected.contains(&h) {
+                continue;
+            }
+            for &[x, y, _] in &wire.points {
+                if x.is_finite() && y.is_finite() {
+                    min = min.min(glam::DVec2::new(x as f64, y as f64));
+                    max = max.max(glam::DVec2::new(x as f64, y as f64));
+                    any = true;
+                }
+            }
+        }
+        if any {
+            let c = (min + max) * 0.5;
+            Some(glam::DVec3::new(c.x, c.y, 0.0))
+        } else {
+            None
+        }
+    }
+
     fn compute_model_space_extents(&self) -> Option<(glam::Vec3, glam::Vec3)> {
         let model_block = self.model_space_block_handle();
         if model_block.is_null() {

src/scene/mspace.rs

@@ -220,7 +220,8 @@ impl Scene {
             Some(c) => c,
             None => return,
         };
-        cam.orbit(delta_x, delta_y);
+        // Floating viewport orbits about its own target (no selection pivot).
+        cam.orbit(delta_x, delta_y, None);
         // yaw_pitch_to_quat(y,p)*Z = (cos(p)*sin(y), -cos(p)*cos(y), sin(p))
         // `camera_for_viewport` reconstructs the rotation so that
         // `rotation * Z == view_direction` exactly (its `yaw = atan2(x, -y)`

src/scene/pick/selection_state.rs

@@ -32,6 +32,10 @@ pub struct SelectionState {
     pub right_press_time: Option<Instant>,
     pub right_dragging: bool,
     pub right_last_pos: Option<Point>,
+    /// World point the current orbit drag revolves around (selection or model
+    /// centre), captured when the drag starts so it stays fixed for the whole
+    /// gesture. `None` when no orbit is in progress. (#229)
+    pub orbit_pivot: Option<glam::DVec3>,
     /// While a command is active, a right-click acts as Enter; the *next*
     /// consecutive right-click opens the context menu instead. This tracks
     /// whether the previous right-click already fired Enter. Reset by any

src/scene/view/camera.rs

@@ -11,7 +11,7 @@
 //
 // Coordinate convention: Z-up world space (same as the rest of OpenCADStudio).
 
-use glam::{vec3, DVec3, Mat4, Quat, Vec3};
+use glam::{DVec3, Mat4, Quat, Vec3};
 use iced::{Point, Rectangle};
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
@@ -246,29 +246,39 @@ impl Camera {
     // ── Navigation ────────────────────────────────────────────────────────
 
     /// Arcball orbit: drag delta (dx, dy) in screen pixels.
-    pub fn orbit(&mut self, delta_x: f32, delta_y: f32) {
+    /// Orbit the view by a screen drag, turntable-style: horizontal drag yaws
+    /// about world +Z, vertical drag pitches about the camera's (always
+    /// horizontal) right axis — so the horizon never banks. `pivot` is the world
+    /// point to revolve around (selection or model centre); `None` keeps the
+    /// current target as the centre. (#229)
+    pub fn orbit(&mut self, delta_x: f32, delta_y: f32, pivot: Option<DVec3>) {
         if delta_x.abs() < 1e-6 && delta_y.abs() < 1e-6 {
             return;
         }
-
+        let old_rot = self.rotation;
         let speed = 0.005_f32;
-        let angle = (delta_x * delta_x + delta_y * delta_y).sqrt() * speed;
-
-        // Screen drag → rotation axis: right drag = rotate around cam_up (Y),
-        // down drag = rotate around cam_right (X). Negate so drag direction
-        // matches intuitive "grab and spin" arcball behaviour.
-        let screen_axis = vec3(-delta_y, -delta_x, 0.0).normalize_or_zero();
 
+        let yaw = Quat::from_rotation_z(-delta_x * speed);
+        self.rotation = (yaw * self.rotation).normalize();
         let cam_right = self.rotation * Vec3::X;
-        let cam_up = self.rotation * Vec3::Y;
-        let world_axis = (cam_right * screen_axis.x + cam_up * screen_axis.y).normalize_or_zero();
-
-        if world_axis.length_squared() < 1e-12 {
-            return;
+        let cur_z = (self.rotation * Vec3::Z).z;
+        let pitched =
+            (Quat::from_axis_angle(cam_right, -delta_y * speed) * self.rotation).normalize();
+        let new_z = (pitched * Vec3::Z).z;
+        // Accept the pitch while the gaze stays clear of the poles, OR when it
+        // moves back AWAY from a pole — so the straight-down default view (z = 1)
+        // can still be tilted out of (a hard `< 0.9995` gate alone would freeze
+        // small drags there). Only a step deeper INTO a pole is rejected.
+        if new_z.abs() < 0.9995 || new_z.abs() < cur_z.abs() {
+            self.rotation = pitched;
         }
 
-        let delta_rot = Quat::from_axis_angle(world_axis, angle);
-        self.rotation = (delta_rot * self.rotation).normalize();
+        // Revolve the target around the pivot by the same rotation delta so the
+        // view orbits the chosen centre instead of the fixed file centre (#229).
+        if let Some(p) = pivot {
+            let delta = self.rotation * old_rot.conjugate();
+            self.target = p + (delta * (self.target - p).as_vec3()).as_dvec3();
+        }
 
         // Sync legacy yaw/pitch for hit-test functions.
         self.sync_yaw_pitch();