refactor(selection): split 31-field SelectionState into five sub-structs

SelectionState now holds view, gesture, input, menu and orbit sub-structs; all 450 access sites updated mechanically with no behavior change. Deletes three write-only dead fields (box_last, box_last_crossing, poly_last_crossing). Hand-rolled clears in commands and dim_viewport route through the new clear methods; bench fixture updated. Full suite: 1976 passed / 0 failed / 25 ignored.

src/scene/camera_ops.rs

@@ -430,7 +430,7 @@ impl Scene {
     /// wrong whenever a tiled viewport is active.
     pub(super) fn active_camera_aspect(&self) -> f32 {
         if self.current_layout == "Model" {
-            let (canvas_w, canvas_h) = self.selection.borrow().vp_size;
+            let (canvas_w, canvas_h) = self.selection.borrow().view.vp_size;
             let tiles = self.model_tiles.borrow();
             let active = self.active_model_tile.get().min(tiles.len().saturating_sub(1));
             if let Some(tile) = tiles.get(active) {
@@ -803,7 +803,7 @@ impl Scene {
             z: view_dir.z as f64,
         };
         entry.view_height = view_height as f64;
-        let (canvas_width, canvas_height) = self.selection.borrow().vp_size;
+        let (canvas_width, canvas_height) = self.selection.borrow().view.vp_size;
         let viewport_width = (upper_right.x - lower_left.x).abs() * canvas_width as f64;
         let viewport_height = (upper_right.y - lower_left.y).abs() * canvas_height as f64;
         if viewport_width > 1e-9 && viewport_height > 1e-9 {
@@ -1556,7 +1556,7 @@ impl Scene {
             return;
         };
 
-        let (canvas_w, canvas_h) = self.selection.borrow().vp_size;
+        let (canvas_w, canvas_h) = self.selection.borrow().view.vp_size;
         let fallback = self.last_render_aspect.get().max(0.01);
         let aspects: Vec<f32> = self
             .model_tiles

src/scene/parametric_constraints.rs

@@ -3068,7 +3068,7 @@ impl super::Scene {
     /// `(id, anchor, outward_screen_direction, label, is_conflicting,
     /// hover_points)` for every enabled, visible constraint whose glyph
     /// projects on-screen.
-    /// `vp_size` is the full canvas size (as `SelectionState::vp_size`
+    /// `vp_size` is the full canvas size (as `SelectionView::vp_size`
     /// reports it), matching what `viewport_edit_frame`/
     /// `active_model_tile_bounds` expect. Mirrors the projection
     /// `crate::app::view` builds its own render list with. The memoised
@@ -3808,7 +3808,7 @@ mod tests {
                 Vector3::new(1.0, 0.0, 0.0),
             ),
         ));
-        scene.selection.borrow_mut().vp_size = (800.0, 600.0);
+        scene.selection.borrow_mut().view.vp_size = (800.0, 600.0);
         let id = scene.parametric_constraint_set_mut(scope).add(
             ConstraintKind::Horizontal,
             vec![ParametricRef::whole(line)],
@@ -3848,7 +3848,7 @@ mod tests {
                 Vector3::new(1.0, 0.0, 0.0),
             ),
         ));
-        scene.selection.borrow_mut().vp_size = (800.0, 600.0);
+        scene.selection.borrow_mut().view.vp_size = (800.0, 600.0);
         let id = scene.parametric_constraint_set_mut(scope).add(
             ConstraintKind::Horizontal,
             vec![ParametricRef::whole(line)],
@@ -3878,7 +3878,7 @@ mod tests {
                 Vector3::new(1.0, 0.0, 0.0),
             ),
         ));
-        scene.selection.borrow_mut().vp_size = (800.0, 600.0);
+        scene.selection.borrow_mut().view.vp_size = (800.0, 600.0);
         let id = scene.parametric_constraint_set_mut(scope).add(
             ConstraintKind::Horizontal,
             vec![ParametricRef::whole(line)],

src/scene/pick/selection_state.rs

@@ -2,9 +2,29 @@ use iced::time::Instant;
 use iced::Point;
 
 /// Mouse / selection interaction state for the viewport.
+///
+/// Split (#32) into five sub-structs by family so a per-frame clone can copy
+/// only the family it needs and gesture clears touch one family at a time.
+/// The `RefCell` around this struct (`Scene::selection`) is untouched.
 #[derive(Clone, Default)]
 pub struct SelectionState {
+    pub view: SelectionView,
+    pub gesture: SelectionGesture,
+    pub input: SelectionInput,
+    pub menu: SelectionMenu,
+    pub orbit: SelectionOrbit,
+}
+
+/// View-dependent snapshot: the canvas size selection geometry is expressed in.
+#[derive(Clone, Default)]
+pub struct SelectionView {
     pub vp_size: (f32, f32),
+}
+
+/// One box-or-lasso gesture: anchor/current corners, crossing sense, and the
+/// in-progress polygon. Cleared together by [`SelectionGesture::clear_left`].
+#[derive(Clone, Default)]
+pub struct SelectionGesture {
     pub box_anchor: Option<Point>,
     /// World point under the box-selection anchor, so the anchor can be
     /// re-projected to screen when the camera zooms/pans mid-drag instead of
@@ -12,14 +32,12 @@ pub struct SelectionState {
     /// (#234)
     pub box_anchor_world: Option<glam::DVec3>,
     pub box_current: Option<Point>,
-    pub box_last: Option<(Point, Point)>,
     pub box_crossing: bool,
     /// Set when a Window / Crossing selection keyword fixed the sense of the
     /// box being drawn. Dragging normally decides it from the direction the
     /// corner travels, which would immediately overwrite what the user just
     /// asked for, so that derivation stands down while this holds.
     pub box_crossing_locked: bool,
-    pub box_last_crossing: bool,
     /// A preview-only selection marquee `(anchor, current, crossing)` in canvas
     /// pixels, drawn identically to a real box-selection (green crossing fill /
     /// blue window fill) but with NO hit-test behaviour. Commands that pick a
@@ -29,14 +47,25 @@ pub struct SelectionState {
     pub poly_active: bool,
     pub poly_points: Vec<Point>,
     pub poly_crossing: bool,
-    pub poly_last_crossing: bool,
-    /// Canvas position the right-click context menu is anchored at while it
-    /// is open. `None` = closed. Its rows are rebuilt from app state every
-    /// frame (`ui::popup::context_menu::build_context_menu`).
-    pub context_menu: Option<Point>,
-    /// Transient UI state of the open context menu (expanded submenu,
-    /// keyboard highlight). Reset every time the menu opens.
-    pub context_menu_ui: ContextMenuUi,
+}
+
+impl SelectionGesture {
+    /// End the in-progress box/lasso gesture (left-button release path).
+    pub fn clear_left(&mut self) {
+        self.box_anchor = None;
+        self.box_anchor_world = None;
+        self.box_current = None;
+        self.box_crossing = false;
+        self.box_crossing_locked = false;
+        self.poly_active = false;
+        self.poly_points.clear();
+        self.poly_crossing = false;
+    }
+}
+
+/// Raw button/pointer state: press positions, drag flags, orbit pivot input.
+#[derive(Clone, Default)]
+pub struct SelectionInput {
     pub last_move_pos: Option<Point>,
     pub left_down: bool,
     pub left_press_pos: Option<Point>,
@@ -47,10 +76,6 @@ 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
@@ -66,6 +91,52 @@ pub struct SelectionState {
     pub zoom_dir_out: bool,
 }
 
+impl SelectionInput {
+    /// Release the left button (click-commit path).
+    pub fn clear_left_buttons(&mut self) {
+        self.left_down = false;
+        self.left_press_pos = None;
+        self.left_press_time = None;
+        self.left_dragging = false;
+    }
+}
+
+/// Right-click context-menu state.
+#[derive(Clone, Default)]
+pub struct SelectionMenu {
+    /// Canvas position the right-click context menu is anchored at while it
+    /// is open. `None` = closed. Its rows are rebuilt from app state every
+    /// frame (`ui::popup::context_menu::build_context_menu`).
+    pub open_at: Option<Point>,
+    /// Transient UI state of the open context menu (expanded submenu,
+    /// keyboard highlight). Reset every time the menu opens.
+    pub ui: ContextMenuUi,
+}
+
+impl SelectionMenu {
+    /// Open the context menu at `at`, discarding the previous menu's
+    /// expanded-submenu / highlight state.
+    pub fn open(&mut self, at: Point) {
+        self.open_at = Some(at);
+        self.ui = ContextMenuUi::default();
+    }
+
+    /// Close the context menu (no-op when it is not open).
+    pub fn close(&mut self) {
+        self.open_at = None;
+        self.ui = ContextMenuUi::default();
+    }
+}
+
+/// Orbit-drag state.
+#[derive(Clone, Default)]
+pub struct SelectionOrbit {
+    /// 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 pivot: Option<glam::DVec3>,
+}
+
 /// Transient state of the open right-click context menu.
 #[derive(Clone, Default)]
 pub struct ContextMenuUi {
@@ -78,36 +149,12 @@ pub struct ContextMenuUi {
 }
 
 impl SelectionState {
-    /// Open the context menu at `at`, discarding the previous menu's
-    /// expanded-submenu / highlight state.
-    pub fn open_context_menu(&mut self, at: Point) {
-        self.context_menu = Some(at);
-        self.context_menu_ui = ContextMenuUi::default();
-    }
-
-    /// Close the context menu (no-op when it is not open).
-    pub fn close_context_menu(&mut self) {
-        self.context_menu = None;
-        self.context_menu_ui = ContextMenuUi::default();
-    }
-
     /// End every left-button selection gesture without disturbing the previous
     /// completed-window record or command-owned preview marquee. Grip editing
     /// owns the left button while engaged and calls this before/after placement
     /// so a small pointer move cannot also arm a box or lasso selection.
     pub fn clear_left_selection_gesture(&mut self) {
-        self.left_down = false;
-        self.left_press_pos = None;
-        self.left_press_time = None;
-        self.left_dragging = false;
-        self.box_anchor = None;
-        self.box_anchor_world = None;
-        self.box_current = None;
-        self.box_crossing = false;
-        self.box_crossing_locked = false;
-        self.poly_active = false;
-        self.poly_points.clear();
-        self.poly_crossing = false;
+        self.input.clear_left_buttons();
+        self.gesture.clear_left();
     }
 }
-

src/scene/preview.rs

@@ -281,7 +281,7 @@ impl Scene {
         self.interim_wire = None;
         // Drop any point-picked window marquee (STRETCH) so it doesn't linger
         // after the command ends before the next mouse move. (#291)
-        self.selection.borrow_mut().preview_box = None;
+        self.selection.borrow_mut().gesture.preview_box = None;
     }
 
     pub fn wire_models_for(&self, handles: &[codec::Handle]) -> Vec<WireModel> {

src/scene/view/render.rs

@@ -4213,7 +4213,7 @@ impl Scene {
         // `CursorMoved` handler — the cube overlay sits above the shader
         // and would otherwise mask the move event from `Program::update`.
         let hover_region = show_interaction.then(|| self.viewcube_hover.get()).flatten();
-        self.selection.borrow_mut().vp_size = (bounds.width, bounds.height);
+        self.selection.borrow_mut().view.vp_size = (bounds.width, bounds.height);
         if bounds.height > 0.0 {
             self.set_render_aspect(bounds.width / bounds.height);
             self.set_render_pixel_scale(bounds.width, bounds.height);