Merge PR #151 from MarekSpodBiedry: Charts: a missing varyColors varies single-series bar colours by point (#143)

# Conflicts:
#	crates/pptx/src/read/chart.rs
#	crates/render/src/chart.rs
#	crates/render/src/tests.rs

crates/pptx/src/read/chart.rs

@@ -195,9 +195,8 @@ fn chart_within(root: &El, mut budget: usize) -> 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");
         // A bar group without c:gapWidth / c:overlap takes the schema's defaults (150 %, 0 %),
         // not the 219 % / -27 % PowerPoint writes into its new charts.
         let bar_group = g.is("barChart") || g.is("bar3DChart");
@@ -618,4 +617,23 @@ mod tests {
         let t = "<c:title><c:tx><c:rich><a:p><a:r><a:t>Mine</a:t></a:r></a:p></c:rich></c:tx></c:title>";
         assert_eq!(chart(r#"<c:autoTitleDeleted val="0"/>"#, t, 1).title.as_deref(), Some("Mine"));
     }
+
+    const NS_CHART: &str = "http://schemas.openxmlformats.org/drawingml/2006/chart";
+
+    fn vary_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_CHART}"><c:chart><c:plotArea>{bar}</c:plotArea></c:chart></c:chartSpace>"#)
+    }
+
+    #[test]
+    fn missing_vary_colors_means_vary_by_point() {
+        assert!(read_chart_xml(vary_xml("").as_bytes()).is_some_and(|c| c.vary_colors));
+    }
+
+    #[test]
+    fn explicit_vary_colors_is_respected() {
+        assert!(read_chart_xml(vary_xml(r#"<c:varyColors val="0"/>"#).as_bytes()).is_some_and(|c| !c.vary_colors));
+        assert!(read_chart_xml(vary_xml(r#"<c:varyColors val="1"/>"#).as_bytes()).is_some_and(|c| c.vary_colors));
+    }
 }

crates/render/src/chart.rs

@@ -44,6 +44,18 @@ fn point_fill(ctx: &Ctx, c: &Chart, i: usize, s: &deckcraft_model::chart::Series
     }
 }
 
+/// 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 s.point_fills.iter().any(|(k, _)| *k == pi) {
+        return point_fill(ctx, c, si, s, pi);
+    }
+    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 polyline(pts: &[Point]) -> BezPath {
     let mut p = BezPath::new();
     for (k, q) in pts.iter().enumerate() {
@@ -619,7 +631,7 @@ fn draw_inner(ctx: &mut RenderContext, rctx: &Ctx, c: &Chart, m: Affine, w: f64,
                     };
                     series_color(rctx, c, slot)
                 } else {
-                    point_fill(rctx, c, *si, s, i)
+                    bar_fill(rctx, c, *si, i, s)
                 };
                 ctx.set_transform(m);
                 ctx.set_paint(color(fill, 1.0));

crates/render/src/tests.rs

@@ -2400,3 +2400,20 @@ fn render_an_emf_file_to_look_at() {
     let img = render_slide(&p, 0, &RenderOpts { scale: 1.0, ..Default::default() });
     let _ = std::fs::write(out, img.to_png());
 }
+
+#[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));
+}