Fills: a gradient without stops takes them from its style, and keeps none when saved (#330)

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

crates/model/src/resolve.rs

@@ -134,11 +134,8 @@ pub fn xfrm(ctx: &Ctx, shape: &Shape) -> Xfrm {
 /// Effective fill and the style colour (`phClr`) to resolve it with.
 pub fn fill(ctx: &Ctx, shape: &Shape) -> (Option<Fill>, Option<Rgba>) {
     let (lp, mp) = parents(ctx, shape);
-    for s in [Some(shape), lp, mp].into_iter().flatten() {
-        if let Some(f) = &s.fill {
-            return (Some(f.clone()), None);
-        }
-        if let Some(st) = &s.style {
+    let style_fill = |s: &Shape| {
+        s.style.as_ref().map(|st| {
             let (idx, col) = &st.fill_ref;
             let ph = ctx.color(col, None);
             let f = match *idx {
@@ -146,7 +143,25 @@ pub fn fill(ctx: &Ctx, shape: &Shape) -> (Option<Fill>, Option<Rgba>) {
                 i if i >= 1001 => ctx.master.theme.format.bg_fills.get((i - 1001) as usize).cloned(),
                 i => ctx.master.theme.format.fills.get((i - 1) as usize).cloned(),
             };
-            return (f, Some(ph));
+            (f, Some(ph))
+        })
+    };
+    for s in [Some(shape), lp, mp].into_iter().flatten() {
+        if let Some(f) = &s.fill {
+            // A gradient without stops (`a:gradFill` with no `a:gsLst`) takes them from the
+            // gradient its style refers to, keeping its own direction, as PowerPoint draws it.
+            if let Fill::Gradient(g) = f
+                && g.stops.is_empty()
+                && let Some((Some(Fill::Gradient(sg)), ph)) = style_fill(s)
+            {
+                let mut g = g.clone();
+                g.stops = sg.stops;
+                return (Some(Fill::Gradient(g)), ph);
+            }
+            return (Some(f.clone()), None);
+        }
+        if let Some(r) = style_fill(s) {
+            return r;
         }
     }
     if shape.text_box {

crates/model/src/tests.rs

@@ -62,6 +62,29 @@ fn shape_style_fill_resolves_through_theme() {
     assert!(ph.is_some());
 }
 
+#[test]
+fn a_gradient_without_stops_takes_them_from_its_style() {
+    // `a:gradFill` with only a direction: PowerPoint fills it with the stops of the theme gradient
+    // the style's fillRef names, in the style's colour, along the shape's own direction.
+    let p = Presentation::default();
+    let s = &p.slides[0];
+    let ctx = Ctx::for_slide(&p, s).unwrap();
+    let own = style::Gradient { stops: vec![], shape: style::GradientShape::Linear { angle: 45.0, scaled: true }, rotate_with_shape: true };
+    let mut st = ShapeStyle::accent(SchemeSlot::Accent2);
+    st.fill_ref.0 = 3;
+    let sh = Shape { style: Some(st.clone()), fill: Some(Fill::Gradient(own.clone())), ..Default::default() };
+    let (f, ph) = resolve::fill(&ctx, &sh);
+    let Some(Fill::Gradient(g)) = f else { panic!("expected a gradient") };
+    let Some(Fill::Gradient(theme)) = p.masters[0].theme.format.fills.get(2).cloned() else { panic!("theme fill 3 is a gradient") };
+    assert_eq!(g.stops, theme.stops);
+    assert_eq!(g.shape, own.shape, "the shape's own direction");
+    assert_eq!(ph, Some(p.masters[0].theme.colors.get(SchemeSlot::Accent2)));
+    // A solid style fill has no stops to give: the gradient stays empty (draws nothing).
+    st.fill_ref.0 = 1;
+    let sh = Shape { style: Some(st), fill: Some(Fill::Gradient(own.clone())), ..Default::default() };
+    assert_eq!(resolve::fill(&ctx, &sh).0, Some(Fill::Gradient(own)));
+}
+
 #[test]
 fn serde_roundtrip() {
     let p = Presentation::default();

crates/pptx/src/write/dml.rs

@@ -78,22 +78,22 @@ pub fn fill(w: &mut W, x: &mut Exp, o: &mut Out, f: &Fill) {
         Fill::Solid { color: c } => solid(w, c),
         Fill::Gradient(g) => {
             w.open("a:gradFill", A::new().a("rotWithShape", if g.rotate_with_shape { "1" } else { "0" }));
-            w.open0("a:gsLst");
+            // No stops: no `a:gsLst`, so the gradient keeps taking them from its style's fill.
             let mut stops = g.stops.clone();
-            if stops.is_empty() {
-                stops.push(deckcraft_model::style::GradientStop { pos: 0.0, color: ColorRef::rgb(deckcraft_color::Rgba::WHITE) });
-            }
             if stops.len() == 1 {
                 let mut s = stops[0].clone();
                 s.pos = 1.0;
                 stops.push(s);
             }
-            for s in &stops {
-                w.open("a:gs", A::new().a("pos", pct(s.pos.clamp(0.0, 1.0))));
-                color(w, &s.color);
-                w.close("a:gs");
+            if !stops.is_empty() {
+                w.open0("a:gsLst");
+                for s in &stops {
+                    w.open("a:gs", A::new().a("pos", pct(s.pos.clamp(0.0, 1.0))));
+                    color(w, &s.color);
+                    w.close("a:gs");
+                }
+                w.close("a:gsLst");
             }
-            w.close("a:gsLst");
             match &g.shape {
                 GradientShape::Linear { angle, scaled } => {
                     w.empty("a:lin", A::new().a("ang", ang(*angle)).a("scaled", if *scaled { "1" } else { "0" }))

crates/pptx/tests/fills.rs

@@ -79,3 +79,26 @@ fn regex_free_strip(s: &str, open: &str, close: &str) -> String {
     let Some(j) = s[i..].find(close).map(|j| j + i + close.len()) else { return s.to_string() };
     format!("{}{}", &s[..i], &s[j..])
 }
+
+#[test]
+fn a_gradient_without_stops_is_saved_without_stops() {
+    // `a:gradFill` with no `a:gsLst` takes its stops from the style's fill in PowerPoint; saving
+    // must not turn it into a gradient of its own (it used to become solid white).
+    use deckcraft_model::style::{Gradient, GradientShape};
+    let mut p = defaults::new_presentation(None);
+    let id = ShapeId(p.alloc_id());
+    let first = p.slides[0].id;
+    let own = Gradient { stops: vec![], shape: GradientShape::Linear { angle: 45.0, scaled: true }, rotate_with_shape: true };
+    p.slide_mut(first).expect("slide").shapes.push(Shape {
+        id,
+        name: "Styled".into(),
+        xfrm: Some(Xfrm::new(10.0, 10.0, 200.0, 100.0)),
+        fill: Some(Fill::Gradient(own.clone())),
+        style: Some(deckcraft_model::ShapeStyle::accent(deckcraft_color::SchemeSlot::Accent1)),
+        ..Default::default()
+    });
+    let bytes = deckcraft_pptx::export(&p).expect("export");
+    let q = deckcraft_pptx::import(&bytes).expect("import");
+    let s = q.slides[0].shapes.iter().find(|s| s.name == "Styled").expect("shape");
+    assert_eq!(s.fill, Some(Fill::Gradient(own)));
+}