feat(spreadsheet-ui): Big Data virtual tab — 1B cells, procedural, timed sort

Close the UI half of the virtualization gap. A new VirtualGrid widget
renders one billion virtual cells (1,000,000 rows × 1,000 columns) from
the engine's VirtualSheet: only the visible range is drawn, values derive
from a hashed (row, col), and a column-header click sorts the full million
rows by permuting an index — with the elapsed time reported in a status
strip, as the reference does.

- virtual_grid.rs (DSL widget, excluded from coverage like grid.rs):
  zebra-striped cells, row/column headers with the sort glyph, gridlines,
  drag-to-pan and wheel scroll, and a 3-state header sort (asc → desc →
  off) delegated to VirtualSheet::sort_rows/reset_sort. All placement and
  hit-testing reuses the measured GridMetrics; text widths reuse
  TextMeasureCache.
- workspace.rs: a "BigData" toolbar button overlays the virtual grid over
  the spreadsheet grid via two child Views toggled with View::set_visible,
  so the existing spreadsheet path is untouched.

Engine: 479 lib tests + integration (grid data-provider commit included).
UI controllers: 119 tests. Coverage: engine 96.67% (data_source.rs 100%),
ui-controllers 99.35% (floors 96).

crates/apps/spreadsheet/spreadsheet-engine/src/data_source.rs

@@ -0,0 +1,414 @@
+//! A grid data-source abstraction: what a grid pulls visible cells from.
+//!
+//! The Makepad datagrid reference can render **one billion virtual cells**
+//! (1,000,000 rows × 1,000 columns) by deriving each value procedurally
+//! from `(row, col)` — nothing is stored, and a header click sorts all a
+//! million rows by permuting an index rather than moving data.
+//!
+//! This module provides the same seam for our engine: [`GridDataSource`]
+//! is the trait a grid renders from, [`SpreadsheetData`] implements it for
+//! the real store, and [`VirtualSheet`] implements it procedurally. The
+//! sort scales because it permutes a `Vec<u32>` of row indices.
+
+use crate::data::{SpreadsheetData, NUM_COLS, NUM_ROWS};
+use crate::util::write_col_letters;
+
+/// The rows/columns a virtual source presents by default: the reference's
+/// headline "one billion cells".
+pub const VIRTUAL_ROWS: u32 = 1_000_000;
+pub const VIRTUAL_COLS: u32 = 1_000;
+
+/// What a grid renders from: a real store or a procedural source.
+pub trait GridDataSource {
+    fn row_count(&self) -> u32;
+    fn col_count(&self) -> u32;
+    /// Display text for a cell at a *view* position (after any sort).
+    fn cell_display(&self, row: u32, col: u32) -> String;
+    /// Sort every row by `key_col`, ascending or descending.
+    fn sort_rows(&mut self, ascending: bool, key_col: u32);
+    /// The column header label (A1 letters by default).
+    fn col_label(&self, col: u32) -> String {
+        let mut buf = String::new();
+        write_col_letters(col, &mut buf);
+        buf
+    }
+}
+
+impl GridDataSource for SpreadsheetData {
+    fn row_count(&self) -> u32 {
+        NUM_ROWS
+    }
+
+    fn col_count(&self) -> u32 {
+        NUM_COLS
+    }
+
+    fn cell_display(&self, row: u32, col: u32) -> String {
+        self.get_display_value(row, col)
+    }
+
+    fn sort_rows(&mut self, ascending: bool, key_col: u32) {
+        SpreadsheetData::sort_rows(self, ascending, key_col);
+    }
+}
+
+/// A procedural, storage-free data source: values are hashed from
+/// `(row, col)`, so a billion cells cost one struct. Sorting permutes a row
+/// index; the cell text and the numeric sort key derive from the same hash,
+/// so sorting by the key sorts what the user sees.
+pub struct VirtualSheet {
+    rows: u32,
+    cols: u32,
+    /// View row → data row. `None` until the first sort (identity order).
+    perm: Option<Vec<u32>>,
+    /// The active sort: `(key column, ascending)`.
+    sort: Option<(u32, bool)>,
+}
+
+/// The reference's 64-bit mix for `(row, col)`.
+fn hash2(row: u64, col: u64) -> u64 {
+    let mut x = row
+        .wrapping_mul(0x9e37_79b9_7f4a_7c15)
+        .wrapping_add(col.wrapping_mul(0xbf58_476d_1ce4_e5b9))
+        .wrapping_add(0x94d0_49bb_1331_11eb);
+    x ^= x >> 30;
+    x = x.wrapping_mul(0xbf58_476d_1ce4_e5b9);
+    x ^= x >> 27;
+    x = x.wrapping_mul(0x94d0_49bb_1331_11eb);
+    x ^ (x >> 31)
+}
+
+const FIRST: [&str; 12] = [
+    "Ada", "Linus", "Grace", "Alan", "Edsger", "Barbara", "Donald", "Margaret", "Ken", "Dennis",
+    "Radia", "Vint",
+];
+const LAST: [&str; 12] = [
+    "Hopper", "Kay", "Lovelace", "Turing", "Dijkstra", "Liskov", "Knuth", "Hamilton", "Thompson",
+    "Ritchie", "Perlman", "Cerf",
+];
+const CITIES: [&str; 10] = [
+    "Amsterdam",
+    "Tokyo",
+    "Berlin",
+    "Lisbon",
+    "Oslo",
+    "Seoul",
+    "Toronto",
+    "Austin",
+    "Zurich",
+    "Kyoto",
+];
+
+impl VirtualSheet {
+    pub fn new(rows: u32, cols: u32) -> Self {
+        Self {
+            rows,
+            cols,
+            perm: None,
+            sort: None,
+        }
+    }
+
+    /// The data row behind a view row (the identity until sorted).
+    pub fn data_row(&self, view_row: u32) -> u32 {
+        match &self.perm {
+            Some(perm) => perm[view_row as usize],
+            None => view_row,
+        }
+    }
+
+    /// Whether the sheet has been sorted (i.e. `perm` is non-trivial).
+    pub fn is_sorted(&self) -> bool {
+        self.perm.is_some()
+    }
+
+    /// The active sort, if any: `(key column, ascending)`.
+    pub fn sort_state(&self) -> Option<(u32, bool)> {
+        self.sort
+    }
+
+    /// Clear the active sort, restoring the identity row order (the "off"
+    /// state of a header sort toggle).
+    pub fn reset_sort(&mut self) {
+        self.perm = None;
+        self.sort = None;
+    }
+
+    /// The numeric sort key for a *data* cell, derived from the same hash
+    /// that renders the text.
+    pub fn value_num(&self, row: u32, col: u32) -> f64 {
+        let h = hash2(row as u64, col as u64);
+        match col % 6 {
+            0 => row as f64,
+            1 => (h % (FIRST.len() * LAST.len()) as u64) as f64,
+            2 => (h % CITIES.len() as u64) as f64,
+            3 => ((h % 2_000_000) as f64 / 100.0) - 10000.0,
+            4 => (h % 1000) as f64 / 10.0,
+            _ => (h % 2) as f64,
+        }
+    }
+
+    /// The rendered text for a *data* cell.
+    pub fn value_text(&self, row: u32, col: u32) -> String {
+        let h = hash2(row as u64, col as u64);
+        match col % 6 {
+            0 => format!("{}", row),
+            1 => {
+                let i = (h % (FIRST.len() * LAST.len()) as u64) as usize;
+                format!("{} {}", FIRST[i % FIRST.len()], LAST[i / FIRST.len()])
+            }
+            2 => CITIES[(h % CITIES.len() as u64) as usize].to_string(),
+            3 => {
+                let v = ((h % 2_000_000) as f64 / 100.0) - 10000.0;
+                format!("{:.2}", v)
+            }
+            4 => format!("{:.1}%", (h % 1000) as f64 / 10.0),
+            _ => {
+                if h.is_multiple_of(2) {
+                    "yes".to_string()
+                } else {
+                    "no".to_string()
+                }
+            }
+        }
+    }
+
+    /// The header label for a column: named for the first six, then
+    /// `Name·1`, `City·1`, … as the reference does.
+    pub fn col_label(&self, col: u32) -> String {
+        let base = ["#", "Name", "City", "Balance", "Score", "Active"];
+        if col < 6 {
+            base[col as usize].to_string()
+        } else {
+            format!("{}·{}", base[(col % 6) as usize], col / 6)
+        }
+    }
+}
+
+impl GridDataSource for VirtualSheet {
+    fn row_count(&self) -> u32 {
+        self.rows
+    }
+
+    fn col_count(&self) -> u32 {
+        self.cols
+    }
+
+    fn cell_display(&self, row: u32, col: u32) -> String {
+        self.value_text(self.data_row(row), col)
+    }
+
+    /// Sort every row by `key_col`, permuting the row index. The keys are
+    /// computed in the comparator like the reference; the elapsed time is
+    /// reported by the caller (the grid's status bar), not here.
+    fn sort_rows(&mut self, ascending: bool, key_col: u32) {
+        let mut perm: Vec<u32> = (0..self.rows).collect();
+        perm.sort_unstable_by(|&a, &b| {
+            let ka = self.value_num(a, key_col);
+            let kb = self.value_num(b, key_col);
+            let ord = ka.partial_cmp(&kb).unwrap_or(std::cmp::Ordering::Equal);
+            let ord = if ascending { ord } else { ord.reverse() };
+            // Deterministic tie-break by data row, independent of direction.
+            ord.then(a.cmp(&b))
+        });
+        self.perm = Some(perm);
+        self.sort = Some((key_col, ascending));
+    }
+
+    fn col_label(&self, col: u32) -> String {
+        VirtualSheet::col_label(self, col)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The hash is deterministic: the same `(row, col)` always yields the
+    /// same value, so cells and sort keys never change between frames.
+    #[test]
+    fn values_are_deterministic() {
+        let a = VirtualSheet::new(1000, 6);
+        let b = VirtualSheet::new(1000, 6);
+        for row in [0u32, 1, 42, 999] {
+            for col in 0..6u32 {
+                assert_eq!(a.value_text(row, col), b.value_text(row, col));
+                assert_eq!(a.value_num(row, col), b.value_num(row, col));
+            }
+        }
+    }
+
+    /// Column 0 is the row index: `#` renders the row number and sorts by
+    /// it.
+    #[test]
+    fn column_zero_is_the_row_index() {
+        let s = VirtualSheet::new(10, 6);
+        assert_eq!(s.value_text(7, 0), "7");
+        assert_eq!(s.value_num(7, 0), 7.0);
+    }
+
+    /// The sort key for a column orders the rendered text: sorting by the
+    /// key sorts what the user sees.
+    #[test]
+    fn sort_key_matches_the_rendered_balance_text() {
+        let s = VirtualSheet::new(1000, 6);
+        for row in 0..100u32 {
+            let text = s.value_text(row, 3);
+            let num = s.value_num(row, 3);
+            // Balance text is the numeric value with two decimals.
+            assert_eq!(text, format!("{:.2}", num), "row {row} balance");
+        }
+    }
+
+    /// After an ascending sort, the key column is non-decreasing along the
+    /// permutation, and the permutation visits every row exactly once.
+    #[test]
+    fn ascending_sort_orders_the_key_column() {
+        let mut s = VirtualSheet::new(10_000, 6);
+        s.sort_rows(true, 3);
+        let perm = s.perm.as_ref().unwrap();
+        assert_eq!(perm.len(), 10_000);
+
+        let mut seen = vec![false; 10_000];
+        let mut prev = f64::NEG_INFINITY;
+        for &data_row in perm.iter() {
+            seen[data_row as usize] = true;
+            let v = s.value_num(data_row, 3);
+            assert!(v >= prev, "balance {v} below previous {prev}");
+            prev = v;
+        }
+        assert!(seen.iter().all(|&b| b), "permutation must be complete");
+    }
+
+    /// Descending sorts the same column the other way.
+    #[test]
+    fn descending_sort_reverses_the_order() {
+        let mut s = VirtualSheet::new(10_000, 6);
+        s.sort_rows(false, 3);
+        let perm = s.perm.as_ref().unwrap();
+        let mut prev = f64::INFINITY;
+        for &data_row in perm.iter() {
+            let v = s.value_num(data_row, 3);
+            assert!(v <= prev);
+            prev = v;
+        }
+    }
+
+    /// Sorting by column 0 is sorting by the row index (ascending is the
+    /// identity order).
+    #[test]
+    fn sorting_by_column_zero_is_by_row_index() {
+        let mut s = VirtualSheet::new(1_000, 6);
+        s.sort_rows(true, 0);
+        let perm = s.perm.as_ref().unwrap();
+        assert_eq!(perm[0], 0);
+        assert_eq!(perm[1], 1);
+        assert_eq!(perm[999], 999);
+
+        s.sort_rows(false, 0);
+        let perm = s.perm.as_ref().unwrap();
+        assert_eq!(perm[0], 999);
+        assert_eq!(perm[999], 0);
+    }
+
+    /// Before any sort, view rows map to themselves; after one, `is_sorted`
+    /// and `sort_state` report it.
+    #[test]
+    fn sort_state_and_identity_before_sorting() {
+        let s = VirtualSheet::new(10, 6);
+        assert!(!s.is_sorted());
+        assert_eq!(s.sort_state(), None);
+        assert_eq!(s.data_row(7), 7);
+
+        let mut s = VirtualSheet::new(10, 6);
+        s.sort_rows(true, 4);
+        assert!(s.is_sorted());
+        assert_eq!(s.sort_state(), Some((4, true)));
+        // `cell_display` now routes through the permutation.
+        let perm = s.perm.clone().unwrap();
+        assert_eq!(s.data_row(0), perm[0]);
+
+        // The "off" state of a header toggle restores identity order.
+        s.reset_sort();
+        assert!(!s.is_sorted());
+        assert_eq!(s.sort_state(), None);
+        assert_eq!(s.data_row(7), 7);
+    }
+
+    /// Column labels: the six base names, then suffixed repeats.
+    #[test]
+    fn column_labels_cycle_the_base_names() {
+        let s = VirtualSheet::new(10, 100);
+        assert_eq!(s.col_label(0), "#");
+        assert_eq!(s.col_label(1), "Name");
+        assert_eq!(s.col_label(5), "Active");
+        assert_eq!(s.col_label(6), "#·1");
+        assert_eq!(s.col_label(7), "Name·1");
+        assert_eq!(s.col_label(13), "Name·2");
+    }
+
+    /// The `SpreadsheetData` implementor delegates to the real store: cell
+    /// display is the formatted value and sorting is the physical sort.
+    #[test]
+    fn spreadsheet_data_implements_the_trait() {
+        let mut sheet = SpreadsheetData::default();
+        sheet.set_cell(0, 0, "3");
+        sheet.set_cell(1, 0, "1");
+        sheet.set_cell(2, 0, "2");
+
+        assert_eq!(sheet.row_count(), NUM_ROWS);
+        assert_eq!(sheet.col_count(), NUM_COLS);
+        assert_eq!(sheet.cell_display(0, 0), "3");
+
+        GridDataSource::sort_rows(&mut sheet, true, 0);
+        assert_eq!(sheet.get_raw(0, 0), "1");
+        assert_eq!(sheet.get_raw(2, 0), "3");
+
+        // The default column label is A1 letters.
+        assert_eq!(sheet.col_label(0), "A");
+        assert_eq!(sheet.col_label(25), "Z");
+        assert_eq!(sheet.col_label(26), "AA");
+    }
+
+    /// A virtual sheet with the default "billion cells" extent reports it.
+    #[test]
+    fn default_extent_is_one_billion_cells() {
+        let s = VirtualSheet::new(VIRTUAL_ROWS, VIRTUAL_COLS);
+        assert_eq!(s.row_count(), 1_000_000);
+        assert_eq!(s.col_count(), 1_000);
+        // A billion cells render from zero stored data.
+        assert!(!s.value_text(999_999, 999).is_empty());
+    }
+
+    /// `VirtualSheet` implements the trait too, so a grid can pull cells
+    /// through the same `GridDataSource` seam for a real or a virtual
+    /// source.
+    #[test]
+    fn virtual_sheet_implements_the_trait() {
+        let mut s = VirtualSheet::new(1_000, 6);
+        assert_eq!(s.row_count(), 1_000);
+        assert_eq!(s.col_count(), 6);
+        assert_eq!(GridDataSource::cell_display(&s, 0, 0), "0");
+        assert_eq!(GridDataSource::col_label(&s, 7), "Name·1");
+
+        GridDataSource::sort_rows(&mut s, false, 3);
+        assert!(s.is_sorted());
+    }
+
+    /// Value text for the Balance column is negative for exactly the rows
+    /// whose numeric key is negative (sign consistency for the red/green
+    /// tint the grid applies).
+    #[test]
+    fn balance_sign_matches_the_text_prefix() {
+        let s = VirtualSheet::new(10_000, 6);
+        for row in 0..1_000u32 {
+            let num = s.value_num(row, 3);
+            let text = s.value_text(row, 3);
+            assert_eq!(
+                text.starts_with('-'),
+                num < 0.0,
+                "row {row}: text {text} vs key {num}"
+            );
+        }
+    }
+}

crates/apps/spreadsheet/spreadsheet-engine/src/lib.rs

@@ -16,6 +16,7 @@
 
 pub mod autofill;
 pub mod data;
+pub mod data_source;
 pub mod dates;
 pub mod formula2;
 pub mod persistence;

crates/apps/spreadsheet/spreadsheet-ui/src/lib.rs

@@ -26,6 +26,7 @@ pub mod sort_state;
 pub mod sparkline;
 pub mod text_measure;
 pub mod trend_chart;
+pub mod virtual_grid;
 pub mod workspace;
 pub mod zoom;
 
@@ -43,5 +44,6 @@ use makepad_widgets::ScriptVm;
 pub fn script_mod(vm: &mut ScriptVm) {
     grid::script_mod(vm);
     trend_chart::script_mod(vm);
+    virtual_grid::script_mod(vm);
     workspace::script_mod(vm);
 }

crates/apps/spreadsheet/spreadsheet-ui/src/virtual_grid.rs

@@ -0,0 +1,411 @@
+//! `VirtualGrid` widget: a virtualized grid over a procedural source.
+//!
+//! Renders one billion virtual cells (1,000,000 rows × 1,000 columns) with
+//! nothing stored: only the visible cells are drawn, values derive from a
+//! hashed `(row, col)`, and a column-header click sorts the full million
+//! rows by permuting an index. This is the reference datagrid's "Big Data"
+//! tab, built on `VirtualSheet` (engine) + `GridMetrics`/`TextMeasureCache`
+//! (measured UI modules).
+//!
+//! The file carries the `script_mod!` DSL and is excluded from coverage
+//! (like `grid.rs` and `trend_chart.rs`); the logic it delegates to lives
+//! in the engine's `data_source.rs` and the measured geometry modules.
+
+use makepad_widgets::*;
+
+use crate::geometry::GridMetrics;
+use crate::text_measure::TextMeasureCache;
+use spreadsheet_engine::data_source::{GridDataSource, VirtualSheet, VIRTUAL_COLS, VIRTUAL_ROWS};
+
+/// Status strip height, in pixels.
+const STATUS_H: f64 = 22.0;
+
+/// In-progress drag state.
+enum VDrag {
+    None,
+    Panning { last: DVec2 },
+    HeaderPending { col: u32, down: DVec2 },
+}
+
+#[derive(Script, ScriptHook, Widget)]
+pub struct VirtualGrid {
+    #[uid]
+    uid: WidgetUid,
+    #[source]
+    source: ScriptObjectRef,
+    #[walk]
+    walk: Walk,
+    #[layout]
+    layout: Layout,
+    #[redraw]
+    #[live]
+    draw_bg: DrawColor,
+    #[live]
+    draw_header_bg: DrawColor,
+    #[live]
+    draw_cell_bg: DrawColor,
+    #[live]
+    draw_grid_line: DrawColor,
+    #[live]
+    draw_text: DrawText,
+    #[live]
+    draw_header_text: DrawText,
+    #[live]
+    pub header_bg_color: Vec4f,
+    #[live]
+    pub header_text_color: Vec4f,
+    #[live]
+    pub cell_bg_color: Vec4f,
+    #[live]
+    pub cell_alt_bg_color: Vec4f,
+    #[live]
+    pub grid_line_color: Vec4f,
+    #[live]
+    pub text_color: Vec4f,
+    #[live]
+    pub pos_text_color: Vec4f,
+    #[live]
+    pub neg_text_color: Vec4f,
+    #[live(110.0)]
+    pub col_width: f32,
+    #[live(24.0)]
+    pub row_height: f32,
+    #[live(76.0)]
+    pub row_header_width: f32,
+    #[live(28.0)]
+    pub col_header_height: f32,
+    #[rust(VirtualSheet::new(VIRTUAL_ROWS, VIRTUAL_COLS))]
+    sheet: VirtualSheet,
+    #[rust]
+    rect: Rect,
+    #[rust]
+    scroll_row: f64,
+    #[rust]
+    scroll_col: f64,
+    #[rust(VDrag::None)]
+    drag: VDrag,
+    /// `(key column, ascending)`, mirroring `sheet.sort_state()`.
+    #[rust]
+    sort_state: Option<(u32, bool)>,
+    /// "sorted 1,000,000 rows by \"X\" ascending in N ms".
+    #[rust]
+    sort_report: String,
+    #[rust]
+    measure: TextMeasureCache,
+    #[rust]
+    last_touch: Option<DVec2>,
+}
+
+impl VirtualGrid {
+    fn metrics(&self) -> GridMetrics {
+        GridMetrics {
+            origin: (self.rect.pos.x, self.rect.pos.y),
+            row_header_width: self.row_header_width as f64,
+            col_header_height: self.col_header_height as f64,
+            default_col_width: self.col_width as f64,
+            default_row_height: self.row_height as f64,
+            col_widths: Vec::new(),
+            row_heights: Vec::new(),
+            frozen_cols: 0,
+            frozen_rows: 0,
+            scroll_col: self.scroll_col,
+            scroll_row: self.scroll_row,
+            num_cols: self.sheet.col_count(),
+            num_rows: self.sheet.row_count(),
+        }
+    }
+
+    fn toggle_sort(&mut self, col: u32) {
+        let t0 = std::time::Instant::now();
+        self.sort_state = match self.sort_state {
+            Some((c, true)) if c == col => {
+                self.sheet.sort_rows(false, col);
+                Some((col, false))
+            }
+            Some((c, false)) if c == col => {
+                self.sheet.reset_sort();
+                None
+            }
+            _ => {
+                self.sheet.sort_rows(true, col);
+                Some((col, true))
+            }
+        };
+        let ms = t0.elapsed().as_millis();
+        self.sort_report = match self.sort_state {
+            Some((c, asc)) => format!(
+                "sorted {} rows by \"{}\" {} in {} ms",
+                self.sheet.row_count(),
+                self.sheet.col_label(c),
+                if asc { "ascending" } else { "descending" },
+                ms
+            ),
+            None => "sort cleared — identity order".to_string(),
+        };
+    }
+
+    fn scroll_by(&mut self, cx: &mut Cx, delta: DVec2) {
+        let cell_w = self.col_width as f64;
+        let cell_h = self.row_height as f64;
+        let body_w = (self.rect.size.x - self.row_header_width as f64).max(1.0);
+        let body_h = (self.rect.size.y - self.col_header_height as f64 - STATUS_H).max(1.0);
+        let vis_cols = (body_w / cell_w).max(1.0);
+        let vis_rows = (body_h / cell_h).max(1.0);
+        let max_scroll_col = (self.sheet.col_count() as f64 - vis_cols).max(0.0);
+        let max_scroll_row = (self.sheet.row_count() as f64 - vis_rows).max(0.0);
+        self.scroll_row = (self.scroll_row + delta.y / cell_h).clamp(0.0, max_scroll_row);
+        self.scroll_col = (self.scroll_col + delta.x / cell_w).clamp(0.0, max_scroll_col);
+        self.redraw(cx);
+    }
+}
+
+impl Widget for VirtualGrid {
+    fn handle_event(&mut self, cx: &mut Cx, event: &Event, _scope: &mut Scope) {
+        match event.hits_with_capture_overload(cx, self.draw_bg.area(), true) {
+            Hit::FingerDown(fe) if fe.is_primary_hit() => {
+                self.last_touch = Some(fe.abs);
+                cx.set_key_focus(self.draw_bg.area());
+                if fe.abs.y < self.rect.pos.y + self.col_header_height as f64 {
+                    if let Some((col, _)) = self.metrics().col_at_x(fe.abs.x) {
+                        self.drag = VDrag::HeaderPending { col, down: fe.abs };
+                    }
+                } else {
+                    self.drag = VDrag::Panning { last: fe.abs };
+                }
+            }
+            Hit::FingerHoverIn(fe) | Hit::FingerHoverOver(fe) => {
+                if fe.abs.y < self.rect.pos.y + self.col_header_height as f64
+                    && fe.abs.x >= self.rect.pos.x + self.row_header_width as f64
+                {
+                    cx.set_cursor(MouseCursor::Grab);
+                } else {
+                    cx.set_cursor(MouseCursor::Default);
+                }
+            }
+            Hit::FingerMove(fe) => match self.drag {
+                VDrag::Panning { last } => {
+                    let delta = last - fe.abs;
+                    self.scroll_by(cx, delta);
+                    self.drag = VDrag::Panning { last: fe.abs };
+                }
+                VDrag::HeaderPending { col, down } => {
+                    if (fe.abs - down).length() > 8.0 {
+                        // Became a pan rather than a click.
+                        self.drag = VDrag::Panning { last: fe.abs };
+                    } else {
+                        self.drag = VDrag::HeaderPending { col, down };
+                    }
+                }
+                VDrag::None => {
+                    if let Some(start) = self.last_touch {
+                        if (fe.abs - start).length() > 8.0 {
+                            self.drag = VDrag::Panning { last: fe.abs };
+                        }
+                    }
+                }
+            },
+            Hit::FingerUp(_) => {
+                if let VDrag::HeaderPending { col, .. } = self.drag {
+                    self.toggle_sort(col);
+                    self.redraw(cx);
+                }
+                self.drag = VDrag::None;
+                self.last_touch = None;
+            }
+            Hit::FingerScroll(fs) => {
+                // A wheel tick scrolls rows vertically or columns
+                // horizontally, matching the grid's own wheel handling.
+                if fs.scroll.y.abs() > f64::EPSILON {
+                    self.scroll_by(cx, dvec2(0.0, fs.scroll.y));
+                } else {
+                    self.scroll_by(cx, dvec2(fs.scroll.x, 0.0));
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn draw_walk(&mut self, cx: &mut Cx2d, _scope: &mut Scope, walk: Walk) -> DrawStep {
+        self.rect = cx.walk_turtle(walk);
+        self.draw_bg.draw_abs(cx, self.rect);
+
+        let m = self.metrics();
+        let cell_w = self.col_width as f64;
+        let cell_h = self.row_height as f64;
+        let header_h = self.col_header_height as f64;
+        let row_hdr_w = self.row_header_width as f64;
+
+        let body_top = self.rect.pos.y + header_h;
+        let body_left = self.rect.pos.x + row_hdr_w;
+        let body_w = (self.rect.size.x - row_hdr_w).max(1.0);
+        let body_h = (self.rect.size.y - header_h - STATUS_H).max(1.0);
+
+        let first_col = m.first_visible_col();
+        let first_row = m.first_visible_row();
+        let vis_cols = (body_w / cell_w).ceil() as u32 + 1;
+        let vis_rows = (body_h / cell_h).ceil() as u32 + 1;
+        let last_col = (first_col + vis_cols).min(m.num_cols);
+        let last_row = (first_row + vis_rows).min(m.num_rows);
+        let sub_col_px = m.scroll_col.fract() * cell_w;
+        let sub_row_px = m.scroll_row.fract() * cell_h;
+
+        // Cells, zebra-striped, only the visible range.
+        for row in first_row..last_row {
+            let y = body_top + (row - first_row) as f64 * cell_h - sub_row_px;
+            for col in first_col..last_col {
+                let x = body_left + (col - first_col) as f64 * cell_w - sub_col_px;
+                let cell_rect = Rect {
+                    pos: dvec2(x, y),
+                    size: dvec2(cell_w, cell_h),
+                };
+                self.draw_cell_bg.color = if row % 2 == 1 {
+                    self.cell_alt_bg_color
+                } else {
+                    self.cell_bg_color
+                };
+                self.draw_cell_bg.draw_abs(cx, cell_rect);
+
+                let text = self.sheet.cell_display(row, col);
+                if !text.is_empty() {
+                    let kind = col % 6;
+                    self.draw_text.color = if kind == 3 {
+                        if text.starts_with('-') {
+                            self.neg_text_color
+                        } else {
+                            self.pos_text_color
+                        }
+                    } else if kind == 0 {
+                        self.header_text_color
+                    } else {
+                        self.text_color
+                    };
+                    let w = self.measure.measure(&text, false);
+                    let tx = match kind {
+                        0 | 3 | 4 => x + cell_w - 8.0 - w,
+                        _ => x + 6.0,
+                    };
+                    let ty = y + (cell_h - 14.0) * 0.5;
+                    self.draw_text.draw_abs(cx, dvec2(tx, ty), &text);
+                }
+            }
+        }
+
+        // Gridlines: a right edge per column and a bottom edge per row in
+        // the visible range.
+        self.draw_grid_line.color = self.grid_line_color;
+        for col in first_col..=last_col {
+            let x = body_left + (col - first_col) as f64 * cell_w - sub_col_px;
+            self.draw_grid_line.draw_abs(
+                cx,
+                Rect {
+                    pos: dvec2(x + cell_w - 1.0, body_top),
+                    size: dvec2(1.0, body_h),
+                },
+            );
+        }
+        for row in first_row..=last_row {
+            let y = body_top + (row - first_row) as f64 * cell_h - sub_row_px;
+            self.draw_grid_line.draw_abs(
+                cx,
+                Rect {
+                    pos: dvec2(body_left, y + cell_h - 1.0),
+                    size: dvec2(body_w, 1.0),
+                },
+            );
+        }
+
+        // Column headers, with the sort glyph on the active column.
+        self.draw_header_bg.color = self.header_bg_color;
+        self.draw_header_bg.draw_abs(
+            cx,
+            Rect {
+                pos: self.rect.pos,
+                size: dvec2(self.rect.size.x, header_h),
+            },
+        );
+        self.draw_header_text.color = self.header_text_color;
+        for col in first_col..last_col {
+            let x = body_left + (col - first_col) as f64 * cell_w - sub_col_px;
+            let mut label = self.sheet.col_label(col);
+            if let Some((sc, asc)) = self.sort_state {
+                if sc == col {
+                    label.push_str(if asc { " ▲" } else { " ▼" });
+                }
+            }
+            self.draw_header_text.draw_abs(
+                cx,
+                dvec2(x + 6.0, self.rect.pos.y + (header_h - 14.0) * 0.5),
+                &label,
+            );
+        }
+
+        // Row headers show the data-row number (1-based), so the
+        // permutation is visible after a sort.
+        self.draw_header_bg.draw_abs(
+            cx,
+            Rect {
+                pos: dvec2(self.rect.pos.x, body_top),
+                size: dvec2(row_hdr_w, body_h),
+            },
+        );
+        for row in first_row..last_row {
+            let y = body_top + (row - first_row) as f64 * cell_h - sub_row_px;
+            let data = self.sheet.data_row(row);
+            let label = format!("{}", data + 1);
+            let tx = self.rect.pos.x + row_hdr_w - 8.0 - label.len() as f64 * 6.0;
+            self.draw_header_text
+                .draw_abs(cx, dvec2(tx, y + (cell_h - 14.0) * 0.5), &label);
+        }
+
+        // Status strip: extents, visible-cell count, and the sort report.
+        let drawn_cols = last_col - first_col;
+        let drawn_rows = last_row - first_row;
+        let status = format!(
+            "{} rows × {} columns = {} virtual cells · drawing {}×{} = {} cells{}",
+            self.sheet.row_count(),
+            self.sheet.col_count(),
+            self.sheet.row_count() as u64 * self.sheet.col_count() as u64,
+            drawn_rows,
+            drawn_cols,
+            drawn_rows * drawn_cols,
+            if self.sort_report.is_empty() {
+                String::new()
+            } else {
+                format!(" · {}", self.sort_report)
+            },
+        );
+        self.draw_header_text.color = self.header_text_color;
+        self.draw_header_text.draw_abs(
+            cx,
+            dvec2(
+                self.rect.pos.x + 10.0,
+                self.rect.pos.y + self.rect.size.y - STATUS_H + 4.0,
+            ),
+            &status,
+        );
+
+        DrawStep::done()
+    }
+}
+
+// The script_mod! macro generates a `script_mod` function.
+// We wrap it in `pub fn` so `lib.rs` can call it.
+script_mod! {
+    use mod.prelude.widgets.*
+
+    mod.widgets.VirtualGrid = #(VirtualGrid::register_widget(vm)) {
+        width: Fill, height: Fill
+        col_width: 110.0, row_height: 24.0, row_header_width: 76.0, col_header_height: 28.0
+        header_bg_color: #x242438, header_text_color: #x8a8aa5
+        cell_bg_color: #x1a1a2e, cell_alt_bg_color: #x1e1e30
+        grid_line_color: #x2a2a3e
+        text_color: #xd8d8e8, pos_text_color: #x81c995, neg_text_color: #xef6a6a
+
+        draw_bg +: { draw_depth: 0.0 color: #x1a1a2e }
+        draw_header_bg +: { draw_depth: 0.1 }
+        draw_cell_bg +: { draw_depth: 0.15 }
+        draw_grid_line +: { draw_depth: 0.2 }
+        draw_text +: { draw_depth: 0.3 color: #xd8d8e8 text_style: theme.font_regular }
+        draw_header_text +: { draw_depth: 0.3 color: #x8a8aa5 text_style: theme.font_bold }
+    }
+}

crates/apps/spreadsheet/spreadsheet-ui/src/workspace.rs

@@ -81,6 +81,10 @@ pub struct SpreadsheetWorkspace {
     /// 0.25s ticker driving the market.
     #[rust]
     timer: Option<Timer>,
+    /// Whether the "Big Data" virtual grid is shown instead of the
+    /// spreadsheet grid.
+    #[rust]
+    big_mode: bool,
 }
 
 impl Widget for SpreadsheetWorkspace {
@@ -751,6 +755,19 @@ impl WidgetMatchEvent for SpreadsheetWorkspace {
             }
         }
 
+        // Big Data view: swap the spreadsheet grid for the virtual grid.
+        if self.button(cx, ids!(bigdata_btn)).clicked(actions) {
+            self.commit_formula_bar_if_dirty(cx);
+            self.big_mode = !self.big_mode;
+            if let Some(mut v) = self.widget(cx, ids!(grid_view)).borrow_mut::<View>() {
+                v.set_visible(cx, !self.big_mode);
+            }
+            if let Some(mut v) = self.widget(cx, ids!(big_view)).borrow_mut::<View>() {
+                v.set_visible(cx, self.big_mode);
+            }
+            self.view.redraw(cx);
+        }
+
         if self.button(cx, ids!(undo_btn)).clicked(actions) {
             self.commit_formula_bar_if_dirty(cx);
             if self.model.borrow_mut().workbook_mut().undo() {
@@ -889,6 +906,8 @@ script_mod! {
             zoom_out_btn := Button { text: "-", width: 28.0, draw_bg +: { color: #x313244 }, draw_text +: { color: #xd8d8e8, text_style +: { font_size: 12.0 } } }
             zoom_reset_btn := Button { text: "100%", width: 44.0, draw_bg +: { color: #x313244 }, draw_text +: { color: #xd8d8e8, text_style +: { font_size: 11.0 } } }
             zoom_in_btn := Button { text: "+", width: 28.0, draw_bg +: { color: #x313244 }, draw_text +: { color: #xd8d8e8, text_style +: { font_size: 12.0 } } }
+            separator6 := View { width: 1.0, height: 26.0, draw_bg +: { color: #x3a3a4e } }
+            bigdata_btn := Button { text: "BigData", width: 60.0, draw_bg +: { color: #x313244 }, draw_text +: { color: #x4fc3f7, text_style +: { font_size: 11.0 } } }
 
             spacer := View { width: Fill }
             status_label := Label { text: "Ready | Workbook Save & Undo Stack Active", draw_text +: { color: #8a8aa5, text_style +: { font_size: 10.5 } } }
@@ -913,8 +932,16 @@ script_mod! {
         }
 
         grid_container := View {
-            width: Fill, height: Fill
-            grid := mod.widgets.SpreadsheetGrid { width: Fill, height: Fill }
+            width: Fill, height: Fill, flow: Overlay
+
+            grid_view := View {
+                width: Fill, height: Fill
+                grid := mod.widgets.SpreadsheetGrid { width: Fill, height: Fill }
+            }
+            big_view := View {
+                width: Fill, height: Fill, visible: false
+                big_grid := mod.widgets.VirtualGrid { width: Fill, height: Fill }
+            }
         }
 
         // Live chart panel: line + candlesticks for the selected row.

tools/test-spreadsheet-coverage.sh

@@ -126,7 +126,7 @@ IGNORE_COMMON='(/cargo/registry|/cargo/git|/rustc/)'
 # grid.rs, ui.rs and workspace.rs are the three files carrying `script_mod!`.
 # Their *testable* logic belongs in a measured module — see geometry.rs —
 # rather than behind this exclusion.
-IGNORE_UI="$IGNORE_COMMON"'|spreadsheet-ui/src/(grid|ui|workspace|trend_chart)\.rs|spreadsheet-ui/src/bin/'
+IGNORE_UI="$IGNORE_COMMON"'|spreadsheet-ui/src/(grid|ui|workspace|trend_chart|virtual_grid)\.rs|spreadsheet-ui/src/bin/'
 
 # Collect every instrumented test binary as `-object` arguments.
 #