Render: table borders draw their dashes, compound bands and diagonals

Explicit cell borders were stroked as plain solid lines (no dash, compound
or cap), and diagonal borders (lnTlToBr, lnBlToTr) were read but never
drawn. Both now go through the shape line stroker; diagonals are drawn
under the cell edges.

Wild synthetic set: border styles slide 5.67 -> 2.26, thick merged-cell
borders 1.20 -> 0.69.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/render/src/lib.rs

@@ -1376,7 +1376,7 @@ fn blur(sigma: f64) -> Filter {
 /// Stroke `path` with `line`. A gradient line is laid out over `extent` (the untrimmed outline the
 /// line belongs to; `path` itself when `None`).
 #[allow(clippy::too_many_arguments)]
-fn stroke(
+pub(crate) fn stroke(
     ctx: &mut RenderContext,
     rctx: &Ctx,
     line: &Line,

crates/render/src/table.rs

@@ -348,6 +348,17 @@ pub fn draw(
             },
         }
     }
+    // Diagonal borders, under the edges: drawn like any line (dashes, compound, caps).
+    for (r, c, rect) in &rects {
+        let Some(cell) = t.cell(*r, *c) else { continue };
+        for (line, a, b) in [(&cell.diag_down, (rect.x0, rect.y0), (rect.x1, rect.y1)), (&cell.diag_up, (rect.x0, rect.y1), (rect.x1, rect.y0))] {
+            let Some(l) = line.as_ref().filter(|l| l.fill.as_ref().is_some_and(|f| !f.is_none())) else { continue };
+            let mut p = BezPath::new();
+            p.move_to(a);
+            p.line_to(b);
+            crate::stroke(ctx, rctx, l, None, &p, None, m, l.width.unwrap_or(1.0).max(0.0), 1.0);
+        }
+    }
     // Borders: explicit cell borders, else the style's grid.
     for (r, c, rect) in &rects {
         let Some(cell) = t.cell(*r, *c) else { continue };
@@ -361,11 +372,16 @@ pub fn draw(
         for (i, e) in edges.iter().enumerate() {
             let line = cell.borders.get(i).and_then(|b| b.as_ref());
             let (col, wd) = match line {
-                Some(l) => match &l.fill {
-                    Some(Fill::Solid { color: cc }) => (rctx.color(cc, None), l.width.unwrap_or(1.0)),
-                    Some(Fill::None) => continue,
-                    _ => continue,
-                },
+                // An explicit border is drawn like any line: dashed, compound, gradient.
+                Some(l) => {
+                    if l.fill.as_ref().is_some_and(|f| !f.is_none()) {
+                        let mut p = BezPath::new();
+                        p.move_to((e.0, e.1));
+                        p.line_to((e.2, e.3));
+                        crate::stroke(ctx, rctx, l, None, &p, None, m, l.width.unwrap_or(1.0).max(0.25), 1.0);
+                    }
+                    continue;
+                }
                 None => match lk.sides.get(i).copied().flatten().or(lk.border) {
                     Some(b) if b.0.a > 0 && b.1 > 0.0 => b,
                     _ => continue,

crates/render/src/tests_wild.rs

@@ -580,3 +580,21 @@ fn a_bevelled_shape_is_lit_from_the_upper_left() {
     let img = render(vec![bevelled(r#"<a:sp3d><a:bevelT w="152400" h="76200"/></a:sp3d>"#)]);
     assert!(close(img.pixel(165, 104), base, 2) && close(img.pixel(165, 165), base, 2));
 }
+
+#[test]
+fn table_borders_take_their_dashes_and_diagonals_are_drawn() {
+    let mut t = deckcraft_model::Table::new(1, 1, 200.0, 100.0);
+    t.style = "none".into();
+    let mut dashed = Line::solid(ColorRef::rgb(RED), 4.0);
+    dashed.dash = Some(deckcraft_model::style::Dash::Preset { name: "dash".into() });
+    if let Some(c) = t.rows.first_mut().and_then(|r| r.cells.first_mut()) {
+        c.borders[2] = Some(dashed);
+        c.diag_down = Some(Line::solid(ColorRef::rgb(Rgba::rgb(0, 0, 255)), 4.0));
+    }
+    let sh = Shape { id: ShapeId(27), xfrm: Some(Xfrm::new(100.0, 100.0, 200.0, 100.0)), kind: ShapeKind::Table(t), ..Default::default() };
+    let img = render(vec![sh]);
+    // Dashes of 4 widths (16 pt) on, 3 (12 pt) off along the top edge, from its start.
+    assert!(close(img.pixel(108, 100), RED, 40) && close(img.pixel(122, 100), WHITE, 30) && close(img.pixel(135, 100), RED, 40));
+    // The diagonal from top-left to bottom-right passes through the middle.
+    assert!(close(img.pixel(200, 150), Rgba::rgb(0, 0, 255), 40), "{:?}", img.pixel(200, 150));
+}