feat: per-viewport grid/snap, adopted from the active viewport

Make grid-snap a per-drawing view setting like grid visibility: drop it
from the persisted OSNAP set (settings.txt) and round-trip it through each
viewport's VPort SNAPMODE instead.

Grid display and grid-snap are now stored per model tile (like render
mode), written to and read from each tile's *Active VPort entry. The live
toggles mirror the active tile, and grid/snap are adopted from the active
viewport whenever it changes — on file load, tab switch, model-tile
activation, and new drawing — so they follow the active viewport rather
than a global preference.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/settings.rs

@@ -27,7 +27,9 @@ const SNAP_ORDER: &[SnapType] = &[
     SnapType::Nearest,
     SnapType::ApparentIntersection,
     SnapType::Parallel,
-    SnapType::Grid,
+    // Grid snap (SNAPMODE) is a per-drawing view setting stored on the VPort,
+    // not a global OSNAP preference, so it is deliberately excluded from the
+    // persisted set. (#121)
 ];
 
 fn snap_id(s: SnapType) -> &'static str {

src/app/update.rs

@@ -340,17 +340,26 @@ impl OpenCADStudio {
         self.persist_settings_if_changed();
     }
 
-    /// Mirror the current grid/snap toggles onto tab `i`'s `*Active` VPort
-    /// entries so a save writes the real display state rather than VPort
-    /// defaults (#121). Cheap; safe to call every frame.
+    /// Mirror the live grid display + grid-snap toggles onto tab `i`'s active
+    /// model tile so a save writes them to that viewport's VPort entry (#121).
     fn sync_vport_display(&mut self, i: usize) {
         let grid_on = self.show_grid;
-        let snap_on =
-            self.snapper.snap_enabled && self.snapper.is_on(crate::snap::SnapType::Grid);
-        let grid_spacing = self.snapper.grid_spacing as f64;
-        self.tabs[i]
-            .scene
-            .set_active_vport_display(grid_on, snap_on, grid_spacing);
+        let snap_on = self.snapper.is_on(crate::snap::SnapType::Grid);
+        self.tabs[i].scene.set_active_tile_grid_snap(grid_on, snap_on);
+    }
+
+    /// Adopt the active viewport's grid display + grid-snap into the live
+    /// toggles. Called on load and whenever the active tab or viewport changes,
+    /// so grid/snap follow the active viewport rather than a global setting.
+    fn adopt_view_display(&mut self, i: usize) {
+        if let Some((grid_on, snap_on)) = self.tabs[i].scene.active_tile_grid_snap() {
+            self.show_grid = grid_on;
+            if snap_on {
+                self.snapper.enabled.insert(crate::snap::SnapType::Grid);
+            } else {
+                self.snapper.enabled.remove(&crate::snap::SnapType::Grid);
+            }
+        }
     }
 
     fn update_inner(&mut self, msg: Message) -> Task<Message> {
@@ -598,11 +607,9 @@ impl OpenCADStudio {
                 // selected — see #21.
                 self.sync_ribbon_from_selection();
                 self.tabs[i].scene.restore_saved_camera();
-                // Grid visibility is a per-drawing view setting — adopt the
-                // opened file's saved state rather than a global preference.
-                if let Some(grid_on) = self.tabs[i].scene.active_vport_grid_on() {
-                    self.show_grid = grid_on;
-                }
+                // Grid/snap are per-drawing view settings — adopt the opened
+                // file's active viewport state rather than a global preference.
+                self.adopt_view_display(i);
                 self.sync_render_mode_to_active_tile(i);
                 self.tabs[i].last_synced_camera_gen = self.tabs[i].scene.camera_generation;
                 self.tabs[i].dirty = false;
@@ -1263,6 +1270,8 @@ impl OpenCADStudio {
                 // fresh tab's defaults (ByLayer) instead of inheriting the
                 // previous tab's last selection.
                 self.sync_ribbon_from_selection();
+                // A fresh drawing starts with grid/snap off (its tile defaults).
+                self.adopt_view_display(self.active_tab);
                 Task::none()
             }
 
@@ -1276,6 +1285,8 @@ impl OpenCADStudio {
                     // CECOLOR / CELTYPE / CELWEIGHT (or its current selection
                     // if there is one), not the prior tab's choice.
                     self.sync_ribbon_from_selection();
+                    // Grid/snap follow the newly active drawing's viewport.
+                    self.adopt_view_display(idx);
                 }
                 Task::none()
             }
@@ -2471,6 +2482,8 @@ impl OpenCADStudio {
                     {
                         self.tabs[i].scene.camera_generation += 1;
                         self.sync_render_mode_to_active_tile(i);
+                        // Grid/snap follow the newly active viewport.
+                        self.adopt_view_display(i);
                     }
                 }
 
@@ -3092,6 +3105,8 @@ impl OpenCADStudio {
                     {
                         self.tabs[i].scene.camera_generation += 1;
                         self.sync_render_mode_to_active_tile(i);
+                        // Grid/snap follow the newly active viewport.
+                        self.adopt_view_display(i);
                         return Task::none();
                     }
                 }

src/scene/mod.rs

@@ -475,6 +475,11 @@ pub(crate) struct ModelTile {
     /// Visual style for this tile alone — each pane carries its own so
     /// changing one tile's render mode never touches the others.
     pub(crate) render_mode: acadrust::entities::ViewportRenderMode,
+    /// Grid display + grid-snap for this viewport alone, round-tripped through
+    /// its VPort entry. The app mirrors the *active* tile's pair into the live
+    /// grid/snap toggles. (#121)
+    pub(crate) grid_on: bool,
+    pub(crate) snap_on: bool,
 }
 
 /// Tolerance for matching two normalized tile coordinates as "the same"
@@ -792,6 +797,8 @@ impl Scene {
                 },
                 camera: Camera::default(),
                 render_mode: acadrust::entities::ViewportRenderMode::Wireframe2D,
+                grid_on: false,
+                snap_on: false,
             }]),
             active_model_tile: std::cell::Cell::new(0),
             selection: Rc::new(RefCell::new(SelectionState::default())),
@@ -5383,14 +5390,17 @@ impl Scene {
     /// Set the model-space camera from the VPORT table's *Active entry.
     /// Returns true if the entry was found and the camera was set.
     fn apply_active_vport_camera(&mut self) -> bool {
-        // Restore the single tile's visual style from the *Active entry,
-        // independent of where the camera itself comes from below.
+        // Restore the single tile's visual style + grid/snap from the *Active
+        // entry, independent of where the camera itself comes from below.
         if let Some(vp) = self.document.vports.iter().find(|v| v.name == "*Active") {
             let mode = vp.render_mode;
+            let (grid_on, snap_on) = (vp.grid_on, vp.snap_on);
             let mut tiles = self.model_tiles.borrow_mut();
             let active = self.active_model_tile.get().min(tiles.len().saturating_sub(1));
             if let Some(t) = tiles.get_mut(active) {
                 t.render_mode = mode;
+                t.grid_on = grid_on;
+                t.snap_on = snap_on;
             }
         }
         // Prefer our named View entry — survives DWG save without being overridden.
@@ -5542,6 +5552,8 @@ impl Scene {
                     rect: Self::vport_to_tile_rect(vp.lower_left, vp.upper_right),
                     camera: cam,
                     render_mode: vp.render_mode,
+                    grid_on: vp.grid_on,
+                    snap_on: vp.snap_on,
                 })
             })
             .collect();
@@ -5573,15 +5585,6 @@ impl Scene {
         }
 
         let table_handle = self.document.vports.handle();
-        // Carry the grid/snap display state from the existing `*Active` entry
-        // across the rebuild — these flags track the in-app toggles and must
-        // not reset to VPort defaults each camera sync. (#121)
-        let display = self
-            .document
-            .vports
-            .iter()
-            .find(|v| v.name == "*Active")
-            .map(|v| (v.grid_on, v.snap_on, v.grid_spacing, v.snap_spacing, v.snap_base));
         let preserved_vps: Vec<acadrust::tables::VPort> = self
             .document
             .vports
@@ -5613,41 +5616,32 @@ impl Scene {
             let (ll, ur) = Self::tile_rect_to_vport(tile.rect);
             let mut entry = self.vport_from_camera("*Active", &tile.camera, ll, ur);
             entry.render_mode = tile.render_mode;
-            if let Some((grid_on, snap_on, grid_spacing, snap_spacing, snap_base)) = display {
-                entry.grid_on = grid_on;
-                entry.snap_on = snap_on;
-                entry.grid_spacing = grid_spacing;
-                entry.snap_spacing = snap_spacing;
-                entry.snap_base = snap_base;
-            }
+            // Each viewport persists its own grid display + grid-snap (#121).
+            entry.grid_on = tile.grid_on;
+            entry.snap_on = tile.snap_on;
             entry.handle = self.document.allocate_handle();
             self.document.vports.add_allow_duplicate(entry);
         }
     }
 
-    /// Stamp the grid/snap display state onto every `*Active` VPort entry so a
-    /// saved file reflects the in-app grid/snap toggles (otherwise other CAD
-    /// apps read VPort defaults). `grid_spacing` is applied to both axes and
-    /// mirrored to the snap spacing. (#121)
-    pub fn set_active_vport_display(&mut self, grid_on: bool, snap_on: bool, grid_spacing: f64) {
-        let spacing = acadrust::types::Vector2 { x: grid_spacing, y: grid_spacing };
-        for vp in self.document.vports.iter_mut().filter(|v| v.name == "*Active") {
-            vp.grid_on = grid_on;
-            vp.snap_on = snap_on;
-            vp.grid_spacing = spacing;
-            vp.snap_spacing = spacing;
+    /// Mirror the live grid/snap toggles onto the *active* model tile so the
+    /// save writes them to that viewport's VPort entry. (#121)
+    pub fn set_active_tile_grid_snap(&self, grid_on: bool, snap_on: bool) {
+        let mut tiles = self.model_tiles.borrow_mut();
+        let active = self.active_model_tile.get().min(tiles.len().saturating_sub(1));
+        if let Some(t) = tiles.get_mut(active) {
+            t.grid_on = grid_on;
+            t.snap_on = snap_on;
         }
     }
 
-    /// Grid visibility stored on the `*Active` VPort entry, applied to the app's
-    /// grid toggle when a file loads (grid is a per-drawing view setting, not a
-    /// global preference). `None` when there is no active entry. (#121)
-    pub fn active_vport_grid_on(&self) -> Option<bool> {
-        self.document
-            .vports
-            .iter()
-            .find(|v| v.name == "*Active")
-            .map(|v| v.grid_on)
+    /// The active model tile's grid display + grid-snap, adopted into the live
+    /// toggles on load and whenever the active viewport / tab changes. `None`
+    /// when there are no tiles. (#121)
+    pub fn active_tile_grid_snap(&self) -> Option<(bool, bool)> {
+        let tiles = self.model_tiles.borrow();
+        let active = self.active_model_tile.get().min(tiles.len().saturating_sub(1));
+        tiles.get(active).map(|t| (t.grid_on, t.snap_on))
     }
 
     /// Set the paper-space camera from the sheet viewport's stored view.
@@ -6344,10 +6338,13 @@ impl Scene {
             )
         };
         let mode = tiles[active].render_mode;
+        let (grid_on, snap_on) = (tiles[active].grid_on, tiles[active].snap_on);
         tiles[active] = ModelTile {
             rect: a,
             camera: cam_now.clone(),
             render_mode: mode,
+            grid_on,
+            snap_on,
         };
         tiles.insert(
             active + 1,
@@ -6355,6 +6352,8 @@ impl Scene {
                 rect: b,
                 camera: cam_now,
                 render_mode: mode,
+                grid_on,
+                snap_on,
             },
         );
     }
@@ -6402,13 +6401,17 @@ impl Scene {
     pub fn set_model_tile_layout(&self, rects: Vec<iced::Rectangle>) {
         let cam_now = self.camera.borrow().clone();
         // Every new pane inherits the active tile's current visual style.
-        let mode = {
+        let (mode, grid_on, snap_on) = {
             let tiles = self.model_tiles.borrow();
             let active = self.active_model_tile.get().min(tiles.len().saturating_sub(1));
             tiles
                 .get(active)
-                .map(|t| t.render_mode)
-                .unwrap_or(acadrust::entities::ViewportRenderMode::Wireframe2D)
+                .map(|t| (t.render_mode, t.grid_on, t.snap_on))
+                .unwrap_or((
+                    acadrust::entities::ViewportRenderMode::Wireframe2D,
+                    false,
+                    false,
+                ))
         };
         let tiles: Vec<ModelTile> = rects
             .into_iter()
@@ -6416,6 +6419,8 @@ impl Scene {
                 rect,
                 camera: cam_now.clone(),
                 render_mode: mode,
+                grid_on,
+                snap_on,
             })
             .collect();
         *self.model_tiles.borrow_mut() = if tiles.is_empty() {
@@ -6428,6 +6433,8 @@ impl Scene {
                 },
                 camera: cam_now,
                 render_mode: mode,
+                grid_on,
+                snap_on,
             }]
         } else {
             tiles