#1786: the live pen stroke is drawn as the ink it commits

While dragging with a pen, the stroke under the pointer was always
painted blue at 2 pt, whatever pen or highlighter was chosen, so the
preview and the committed ink disagreed (a highlighter previewed as a
thin blue line). The preview now uses the colour and width draw.stroke
stores (pen blue and 2 pt by default, 0.5-40 pt, whole points) and the
translucency Ink shapes are painted with above 8 pt.

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

crates/ui-egui/src/grid/interact.rs

@@ -225,10 +225,10 @@ fn handle_draw_tool(app: &mut SheetApp, input: &InteractionInput<'_>) -> bool {
                         ))
                     })
                     .collect();
-                input
-                    .ui
-                    .painter()
-                    .add(egui::epaint::PathShape::line(pts, egui::epaint::PathStroke::new(2.0 * geo.z, Color32::from_rgb(0x1F, 0x5F, 0xC9))));
+                // The line under the pointer is the ink the stroke will commit (#1786).
+                let theme = app.session.active().map(|d| d.wb.theme.clone()).unwrap_or_default();
+                let (color, width) = pen_ink(&app.session.draw_color, app.session.draw_width, &theme);
+                input.ui.painter().add(egui::epaint::PathShape::line(pts, egui::epaint::PathStroke::new(width * geo.z, color)));
             }
             if resp.drag_stopped() && app.grid.ink.len() >= 2 {
                 let pts: Vec<[f32; 2]> = std::mem::take(&mut app.grid.ink);
@@ -249,6 +249,17 @@ fn handle_draw_tool(app: &mut SheetApp, input: &InteractionInput<'_>) -> bool {
     false
 }
 
+/// The colour and width (points) of the ink a pen stroke commits, as `draw.stroke` stores it (the
+/// pen's colour, pen blue by default; its width, 2 pt by default, kept to 0.5–40 pt and stored
+/// whole) and as Ink shapes paint it (a highlighter, over 8 pt, is translucent).
+pub(crate) fn pen_ink(color: &str, width: f32, theme: &gridcraft_engine::model::Theme) -> (Color32, f32) {
+    let pen_blue = gridcraft_engine::model::Color::rgb(0x1F, 0x5F, 0xC9);
+    let line = gridcraft_engine::model::Color::from_hex(color).unwrap_or(pen_blue);
+    let width = if width <= 0.0 { 2.0 } else { width }.clamp(0.5, 40.0).round().max(1.0);
+    let color = line.resolve(theme).map(crate::theme::color32).unwrap_or(Color32::from_rgb(0x1F, 0x5F, 0xC9));
+    (if width > 8.0 { color.gamma_multiply(0.45) } else { color }, width)
+}
+
 fn handle_header_autofit(app: &mut SheetApp, input: &InteractionInput<'_>) -> bool {
     let (geo, sh, sel, pos) = (input.geo, input.sheet, &input.selection, input.position);
     let (in_col_header, in_row_header) = (input.in_column_header, input.in_row_header);
@@ -1044,3 +1055,20 @@ pub fn point_move(app: &mut SheetApp, ed: &mut EditState, dr: i64, dc: i64, exte
     ed.point_anchor = Some((sheet, anchor));
     app.grid.ensure_visible = true;
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn the_pen_preview_is_the_ink_the_stroke_commits() {
+        // #1786: the preview was always blue at 2 pt, whatever the pen.
+        let theme = gridcraft_engine::model::Theme::default();
+        assert_eq!(pen_ink("#C00000", 3.0, &theme), (Color32::from_rgb(0xC0, 0, 0), 3.0));
+        assert_eq!(pen_ink("", 0.0, &theme), (Color32::from_rgb(0x1F, 0x5F, 0xC9), 2.0), "no pen chosen yet: pen blue, 2 pt");
+        assert_eq!(pen_ink("not a colour", 0.2, &theme), (Color32::from_rgb(0x1F, 0x5F, 0xC9), 1.0));
+        // A highlighter is wide and translucent, as the committed ink is painted.
+        let (c, w) = pen_ink("#FFFF00", 12.0, &theme);
+        assert_eq!((c, w), (Color32::from_rgb(0xFF, 0xFF, 0).gamma_multiply(0.45), 12.0));
+    }
+}

docs/ui-parity.md

@@ -1,6 +1,6 @@
 # UI parity
 
-> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-11-02 · **Change:** minor (RefEdit reference boxes in dialogs: Goal Seek, Solver and Data Analysis use them, the arrow keys select while a dialog is collapsed and F4 cycles a reference's anchors; earlier: Python cells: Python mode in the formula bar; earlier: Insert › Equation and the equation editor; earlier: every floating object selects, resizes from eight handles and deletes with the keyboard; earlier: Formulas › Error Checking › Trace Error; trace arrows stay through a zoom (#3097); earlier: Page Setup sets the page order, Down, then over or Over, then down, which printing, the print preview, Page Break Preview and Page Layout view follow; earlier: Formulas › Function Library as labelled buttons with category menus; Recently Used and the Insert Function categories; Esc leaves a File-page text field before closing the view; earlier: checkbox cells print as boxes; Ctrl+arrow and Ctrl+Shift+arrow while pointing a formula reference; editing a hyperlink loads its existing fields; AutoSum over a selected row puts its total to the right; ribbon catalog count 276 / 292) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-10 · **Last updated:** 2026-11-03 · **Change:** minor (the Draw tab's live stroke preview uses the pen's colour and thickness; earlier: RefEdit reference boxes in dialogs: Goal Seek, Solver and Data Analysis use them, the arrow keys select while a dialog is collapsed and F4 cycles a reference's anchors; earlier: Python cells: Python mode in the formula bar; earlier: Insert › Equation and the equation editor; earlier: every floating object selects, resizes from eight handles and deletes with the keyboard; earlier: Formulas › Error Checking › Trace Error; trace arrows stay through a zoom (#3097); earlier: Page Setup sets the page order, Down, then over or Over, then down, which printing, the print preview, Page Break Preview and Page Layout view follow; earlier: Formulas › Function Library as labelled buttons with category menus; Recently Used and the Insert Function categories; Esc leaves a File-page text field before closing the view; earlier: checkbox cells print as boxes; Ctrl+arrow and Ctrl+Shift+arrow while pointing a formula reference; editing a hyperlink loads its existing fields; AutoSum over a selected row puts its total to the right; ribbon catalog count 276 / 292) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Interaction, controls and feel, against Excel. Part of [target-app-parity.md](target-app-parity.md).
 **UI/UX fidelity: ~55% ready, 50–80 h** (estimated). Ribbon command coverage is measured
@@ -237,6 +237,7 @@ scrollbar bugs 2–4 · pixel/feel pass against observed Excel 7–12.
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-11-03 | minor | Draw tab: the stroke drawn under the pointer while dragging a pen is the ink that will be committed, in the pen's colour and thickness (translucent for a highlighter), instead of always blue at 2 pt (#1786) |
 | 2026-11-02 | minor | RefEdit reference boxes in dialogs: pick a range on the grid, collapse the dialog while selecting; Goal Seek, Solver (with the Model Range of Load/Save) and Data Analysis use them; while collapsed the arrow keys move the selection and Shift+arrow extends it, F4 cycles a reference's anchors, a click elsewhere keeps the box picking, a dialog opened over a picking one puts the selection back, OK stays on the sheet its command showed, and scripted cancel and confirm end a pick like the buttons; the dialog's sheet is followed through the recorded undo steps, so a sheet deleted and recreated under its name is not taken for it and an undo of the deletion brings it back; a box the dialog stops showing is no longer picked into |
 | 2026-11-02 | minor | Python mode edits a cell's code in the formula bar's code editor (Ctrl+Alt+Shift+P, `=PY` then Tab, editing a Python cell), with the PY badge beside fx; its keys apply in input order, also several in one frame, and Ctrl+Enter commits through `python.set` (empty code clears the cell), keeping the code and showing the command's message when the code is refused |
 | 2026-11-02 | minor | Insert › Symbols: Equation split button (access keys N E), a gallery of examples, and an equation editor with quick-insert buttons, the error underlined at its position and a live preview; double-clicking an equation edits it |