ElyDoc: a page stays centred and zoom stays on the page; only a sheet grows past its size (R2.7)

crates/ely-lok/src/view/scroll.rs

@@ -49,9 +49,11 @@ impl LokView {
             self.geom.twips_of(self.viewport.0) - fx,
             self.geom.twips_of(self.viewport.1) - fy,
         );
-        // Room past the target, in print twips for later zooms.
-        let need = self.print_of((x + w + vw + fx, y + h + vh + fy));
-        self.reach = (self.reach.0.max(need.0), self.reach.1.max(need.1));
+        // Only a sheet grows where it jumps; pages keep their size.
+        if self.sheet.is_some() {
+            let need = self.print_of((x + w + vw + fx, y + h + vh + fy));
+            self.reach = (self.reach.0.max(need.0), self.reach.1.max(need.1));
+        }
         if x >= fx && (x < fx + self.scroll.0 || x + w > fx + self.scroll.0 + vw) {
             self.scroll.0 = x - fx - vw / 2;
         }

crates/ely-lok/src/view/tests.rs

@@ -359,6 +359,8 @@ fn a_moved_cursor_scrolls_into_view_and_a_still_one_does_not() {
             view.scroll_by(0.0, 1_000_000.0, cx);
             view.apply_batch(batch(), None, cx);
             assert_eq!(view.scroll.1, 0, "a still cursor leaves the scroll alone");
+            // Only a sheet grows past the kernel's size.
+            view.sheet = Some(crate::sheet::Geometry::default());
             let far = view.doc_size.1 + 20_000;
             let cell = crate::Cell {
                 cursor: Some((1418, far, 1280, 277)),

crates/ely-lok/src/view/tests/fit.rs

@@ -88,3 +88,30 @@ fn a_resized_slide_reaches_the_view_and_still_fits() {
         })
     });
 }
+
+#[test]
+fn a_page_stays_centred_when_the_cursor_moves() {
+    let Some(install) = crate::client::tests::install() else {
+        eprintln!("SKIP: no pinned LOK build");
+        return;
+    };
+    let cx = gpui::TestAppContext::single();
+    cx.update(|app| {
+        let (view, _) = live_view(app, &install);
+        view.update(app, |view, cx| {
+            let wide = Bounds { origin: point(px(0.0), px(0.0)), size: size(px(2400.0), px(900.0)) };
+            view.prepare(wide);
+            let centred = view.spare.0;
+            assert!(centred > 0.0, "a page narrower than the view sits centred");
+            view.show((1440, 1440, 20, 300), cx);
+            view.prepare(wide);
+            assert_eq!(view.spare.0, centred, "moving the cursor keeps it centred");
+            let narrow = Bounds { origin: point(px(0.0), px(0.0)), size: size(px(800.0), px(900.0)) };
+            view.prepare(narrow);
+            view.set_zoom(2.0, cx);
+            view.prepare(narrow);
+            let right = view.scroll.0 + view.geom.twips_of(view.viewport.0);
+            assert!(right <= view.doc_size.0, "no grey past the page: {right} > {}", view.doc_size.0);
+        })
+    });
+}