Keep overflow text visible when its source cell scrolls out of view

Fixes #1613

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/grid.rs

@@ -1035,7 +1035,9 @@ pub(crate) fn paint_quadrant(
     let (r0, r1) = rows;
     let (c0, c1) = cols;
     let range = RangeRef::new(CellRef::new(r0, c0), CellRef::new(r1, c1));
-    let merges: Vec<RangeRef> = sh.merges.iter().filter(|m| m.intersects(&range)).copied().collect();
+    // Merges are looked up 20 columns beyond the quadrant too: text overflowing in from off-screen cells stops at them.
+    let near = RangeRef::new(CellRef::new(r0, c0.saturating_sub(20)), CellRef::new(r1, c1.saturating_add(20).min(MAX_COLS - 1)));
+    let merges: Vec<RangeRef> = sh.merges.iter().filter(|m| m.intersects(&near)).copied().collect();
     let in_merge = |c: CellRef| merges.iter().find(|m| m.contains(c)).copied();
     // Gridlines.
     if sh.show_gridlines {
@@ -1089,8 +1091,25 @@ pub(crate) fn paint_quadrant(
         }
         looks.push((anchor, rect, lk, cfl));
     }
+    // Text cells just outside the quadrant whose text may overflow into it: the nearest non-empty
+    // cell left of `c0` and right of `c1` in each row (within the same frozen / scrolled pane).
+    let mut outside: Vec<(CellRef, Rect, Look, Option<CfLook>)> = Vec::new();
+    let same_pane = |col: u32| (col < geo.fc) == (c0 < geo.fc);
+    for r in r0..=r1 {
+        if sh.row_height(r) == 0.0 {
+            continue;
+        }
+        let left = (c0.saturating_sub(20)..c0).rev().map(|col| CellRef::new(r, col)).find(|&n| !empty_ok(n));
+        let right = (c1.saturating_add(1)..=c1.saturating_add(20).min(MAX_COLS - 1)).map(|col| CellRef::new(r, col)).find(|&n| !empty_ok(n));
+        for n in [left, right].into_iter().flatten() {
+            if same_pane(n.col) && sh.col_width(n.col) > 0.0 && in_merge(n).is_none() {
+                let (lk, cfl) = look(wb, si, sh, n, cf);
+                outside.push((n, geo.cell_rect(sh, n), lk, cfl));
+            }
+        }
+    }
     // Text and per-cell decorations.
-    for (c, rect, lk, cfl) in &looks {
+    for (c, rect, lk, cfl) in looks.iter().chain(&outside) {
         let c = *c;
         if let Some(picture) = sh.cell_pictures.get(&c) {
             crate::cell_pictures::paint(p, *rect, picture);

crates/ui-egui/tests/text_overflow_scroll.rs

@@ -0,0 +1,110 @@
+//! Overflowing text stays visible in its empty neighbours when its own cell is scrolled out (#1613).
+
+use egui::{Rect, Shape};
+use gridcraft_engine::Session;
+use gridcraft_engine::core::CellRef;
+use gridcraft_ui_egui::{SheetApp, grid::Geo};
+use serde_json::json;
+
+type Harness = egui_kittest::Harness<'static, SheetApp>;
+
+const LEFT: &str = "This is a very long left-aligned text that overflows into many empty neighbouring cells";
+const RIGHT: &str = "This is a very long right-aligned text that overflows into many empty neighbouring cells";
+
+fn harness(setup: impl FnOnce(&mut Session)) -> Harness {
+    let mut s = Session::new();
+    s.new_workbook();
+    setup(&mut s);
+    s.execute("selection.set", json!({"range": "A20"})).unwrap();
+    let mut h = egui_kittest::Harness::builder().with_size(egui::vec2(1200.0, 800.0)).build_ui_state(
+        |ui, app: &mut SheetApp| {
+            app.logic(ui.ctx());
+            app.ui(ui);
+        },
+        SheetApp::new(s, Default::default()),
+    );
+    h.run_steps(4);
+    h
+}
+
+/// Scroll so that `col` is the first column of the scrolled area.
+fn scroll_to_col(h: &mut Harness, col: u32) {
+    let app = h.state_mut();
+    let sheet = app.session.active().unwrap().wb.active().unwrap();
+    let fc = sheet.freeze.map(|f| f.1).unwrap_or(0);
+    let x = (sheet.col_left(col) - sheet.col_left(fc)) as f32;
+    app.view_mut().unwrap().scroll.x = x;
+    h.run_steps(4);
+}
+
+/// Clip rects of the painted text shapes whose text is `text`.
+fn text_clips(h: &Harness, text: &str) -> Vec<Rect> {
+    h.output()
+        .shapes
+        .iter()
+        .filter_map(|s| match &s.shape {
+            Shape::Text(t) if t.galley.job.text == text => Some(s.clip_rect),
+            _ => None,
+        })
+        .collect()
+}
+
+fn cell_rect(h: &Harness, cell: &str) -> Rect {
+    let app = h.state();
+    let sheet = app.session.active().unwrap().wb.active().unwrap();
+    let geo = Geo::new(sheet, app.grid.rect.unwrap(), app.view().scroll);
+    geo.cell_rect(sheet, CellRef::parse(cell).unwrap())
+}
+
+#[test]
+fn overflow_text_stays_visible_when_source_cell_scrolls_out_left() {
+    let mut h = harness(|s| {
+        s.execute("cell.set", json!({"cell": "B1", "input": LEFT})).unwrap();
+    });
+    assert!(!text_clips(&h, LEFT).is_empty(), "B1 is drawn before scrolling");
+    scroll_to_col(&mut h, 2);
+    let c1 = cell_rect(&h, "C1");
+    let clips = text_clips(&h, LEFT);
+    assert!(clips.iter().any(|r| r.intersects(c1.shrink(1.0))), "B1's overflow is still drawn into C1 after scrolling: {clips:?}");
+}
+
+#[test]
+fn right_aligned_overflow_stays_visible_when_source_cell_is_right_of_view() {
+    let mut h = harness(|s| {
+        s.execute("cell.set", json!({"cell": "Z1", "input": RIGHT})).unwrap();
+        s.execute("home.formatCells", json!({"range": "Z1", "style": {"align": {"h": "Right"}}})).unwrap();
+    });
+    // Scroll so that Z1 starts just past the right edge of the cell area.
+    {
+        let app = h.state_mut();
+        let sheet = app.session.active().unwrap().wb.active().unwrap();
+        let geo = Geo::new(sheet, app.grid.rect.unwrap(), app.view().scroll);
+        let x = sheet.col_left(25) as f32 - (geo.cells.width() - geo.frozen_w) / geo.z - 2.0;
+        app.view_mut().unwrap().scroll.x = x;
+    }
+    h.run_steps(4);
+    let (y1, z1, cells) = {
+        let app = h.state();
+        let sheet = app.session.active().unwrap().wb.active().unwrap();
+        let geo = Geo::new(sheet, app.grid.rect.unwrap(), app.view().scroll);
+        (geo.cell_rect(sheet, CellRef::parse("Y1").unwrap()), geo.cell_rect(sheet, CellRef::parse("Z1").unwrap()), geo.cells)
+    };
+    assert!(z1.left() >= cells.right(), "Z1 is out of view on the right ({z1:?} vs {cells:?})");
+    let visible = y1.intersect(cells).shrink(1.0);
+    let clips = text_clips(&h, RIGHT);
+    assert!(clips.iter().any(|r| r.intersects(visible)), "Z1's overflow is drawn into Y1: {clips:?} vs {visible:?}");
+}
+
+#[test]
+fn scrolled_overflow_does_not_draw_over_frozen_columns() {
+    let mut h = harness(|s| {
+        s.execute("cell.set", json!({"cell": "C1", "input": LEFT})).unwrap();
+        s.execute("view.freezePanes", json!({"cell": "B2"})).unwrap();
+    });
+    scroll_to_col(&mut h, 4);
+    let a1 = cell_rect(&h, "A1");
+    let e1 = cell_rect(&h, "E1");
+    let clips = text_clips(&h, LEFT);
+    assert!(clips.iter().any(|r| r.intersects(e1.shrink(1.0))), "C1's overflow reaches E1: {clips:?}");
+    assert!(clips.iter().all(|r| !r.intersects(a1.shrink(1.0))), "C1's overflow stays out of frozen column A: {clips:?}");
+}