Charts: a missing varyColors varies single-series bar colours by point (#143)

crates/pptx/src/read/chart.rs

@@ -150,9 +150,8 @@ pub(crate) fn chart_from(root: &El) -> Option<Chart> {
             "surfaceChart" | "surface3DChart" => ChartType::Surface,
             _ => continue,
         };
-        if let Some(v) = g.child_val("varyColors") {
-            c.vary_colors = v == "1" || v == "true";
-        }
+        // A missing <c:varyColors> means "vary by point" (the schema default is true), as PowerPoint draws it.
+        c.vary_colors = g.child_val("varyColors").is_none_or(|v| v == "1" || v == "true");
         if let Some(v) = g.child_val("gapWidth").and_then(|v| v.parse::<f64>().ok()) {
             c.gap_width = (v / 100.0).clamp(0.0, 5.0);
         }
@@ -225,3 +224,27 @@ pub(crate) fn chart_from(root: &El) -> Option<Chart> {
     }
     Some(c)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::read_chart_xml;
+
+    const NS: &str = "http://schemas.openxmlformats.org/drawingml/2006/chart";
+
+    fn xml(vary: &str) -> String {
+        let ser = r#"<c:ser><c:idx val="0"/><c:order val="0"/></c:ser>"#;
+        let bar = format!(r#"<c:barChart><c:barDir val="col"/><c:grouping val="clustered"/>{vary}{ser}</c:barChart>"#);
+        format!(r#"<c:chartSpace xmlns:c="{NS}"><c:chart><c:plotArea>{bar}</c:plotArea></c:chart></c:chartSpace>"#)
+    }
+
+    #[test]
+    fn missing_vary_colors_means_vary_by_point() {
+        assert!(read_chart_xml(xml("").as_bytes()).is_some_and(|c| c.vary_colors));
+    }
+
+    #[test]
+    fn explicit_vary_colors_is_respected() {
+        assert!(read_chart_xml(xml(r#"<c:varyColors val="0"/>"#).as_bytes()).is_some_and(|c| !c.vary_colors));
+        assert!(read_chart_xml(xml(r#"<c:varyColors val="1"/>"#).as_bytes()).is_some_and(|c| c.vary_colors));
+    }
+}

crates/render/src/chart.rs

@@ -36,6 +36,18 @@ fn series_fill(ctx: &Ctx, c: &Chart, i: usize, s: Option<&deckcraft_model::chart
     }
 }
 
+/// Fill of one bar: a `<c:dPt>` fill wins, and a single-series chart that varies colours by point uses one accent per point
+/// (not waterfalls, which are never read from a `<c:barChart>`).
+fn bar_fill(ctx: &Ctx, c: &Chart, si: usize, pi: usize, s: &deckcraft_model::chart::Series) -> Rgba {
+    if let Some((_, Fill::Solid { color: cc })) = s.point_fills.iter().find(|(k, _)| *k == pi) {
+        return ctx.color(cc, None);
+    }
+    if c.vary_colors && c.series.len() == 1 && s.fill.is_none() && c.kind != ChartType::Waterfall {
+        return series_color(ctx, c, pi);
+    }
+    series_fill(ctx, c, si, Some(s))
+}
+
 fn label(ctx: &mut RenderContext, rctx: &Ctx, m: Affine, text: &str, r: Rect, size: f64, align: Align, anchor: Anchor, col: Rgba, bold: bool) {
     let mut body = TextBody::from_text(text);
     body.body.inset_l = Some(0.0);
@@ -291,7 +303,7 @@ pub fn draw(ctx: &mut RenderContext, rctx: &Ctx, c: &Chart, m: Affine, w: f64, h
                     Rect::new(plot.x0 + start, to_v(b), plot.x0 + start + bar, to_v(a))
                 };
                 ctx.set_transform(m);
-                ctx.set_paint(color(series_fill(rctx, c, si, Some(s)), 1.0));
+                ctx.set_paint(color(bar_fill(rctx, c, si, i, s), 1.0));
                 ctx.fill_rect(&r.abs());
                 if c.data_labels {
                     let t = fmt_num(s.values.get(i).copied().flatten().unwrap_or(0.0));

crates/render/src/tests.rs

@@ -523,3 +523,20 @@ fn hyperlinks_draw_in_the_hyperlink_colour_underlined() {
     let own = px(&run_deck(RunProps { link, fill: red.clone(), ..Default::default() }));
     assert_eq!(diff(&own, &px(&run_deck(RunProps { fill: red, underline: Some("sng".into()), ..Default::default() }))), 0);
 }
+
+#[test]
+fn single_series_column_chart_varies_colours_by_point() {
+    let render = |vary: bool| {
+        let mut c = Chart::sample(ChartType::Column);
+        c.series.truncate(1);
+        c.vary_colors = vary;
+        let sh = Shape {
+            id: ShapeId(800),
+            xfrm: Some(Xfrm::new(50.0, 50.0, 400.0, 300.0)),
+            kind: ShapeKind::Chart(Box::new(c)),
+            ..Default::default()
+        };
+        render_slide(&deck_with(vec![sh]), 0, &RenderOpts { scale: 1.0, ..Default::default() }).pixels
+    };
+    assert_ne!(render(true), render(false));
+}