Integration: #1451 screened outer glows and blended shadows isolate the spread from the paper

crates/render/src/color.rs

@@ -202,7 +202,11 @@ pub(crate) fn overprints(f: &Frame, swatch: &str, tint: f32, flag: bool) -> bool
 pub(crate) fn spread_blends(doc: &Document, sp: &designcraft_doc::Spread) -> bool {
     let blends = |it: &Item| {
         let mut any = false;
-        it.walk(&mut |i| any |= i.blend != Default::default());
+        // A screened glow or a shadow with a blend mode blends with the objects below too, not the paper.
+        let fx_blends = |e: &designcraft_doc::Effects| {
+            (e.outer_glow.on && e.outer_glow.mode != Default::default()) || (e.drop_shadow.on && e.drop_shadow.mode != Default::default())
+        };
+        it.walk(&mut |i| any |= i.blend != Default::default() || fx_blends(&i.effects));
         any
     };
     sp.items.iter().any(|i| blends(i)) || doc.parents.iter().any(|p| p.items.iter().any(|i| blends(i)))

crates/render/tests/it/effects.rs

@@ -178,6 +178,23 @@ fn outer_glow_blends_with_its_mode() {
     assert!(s[2] > n[2] + 25, "screen keeps the backdrop's blue: {s:?} vs normal {n:?}");
 }
 
+/// A screened glow over blank paper shows in its colour: it blends with the objects below, and
+/// the paper is not one of them.
+#[test]
+fn screened_outer_glow_shows_on_blank_paper() {
+    let mut d = doc();
+    let id = rect_item(&mut d, Rect::new(50.0, 50.0, 110.0, 110.0), "[Black]");
+    let g = &mut d.item_mut(id).unwrap().effects.outer_glow;
+    g.on = true;
+    g.size = 12.0;
+    g.color = "C=0 M=0 Y=100 K=0".into();
+    g.opacity = 1.0;
+    g.mode = designcraft_color::BlendMode::Screen;
+    let img = render(&d);
+    let p = img.pixel(46, 80);
+    assert!(p[2] < 200 && p[0] > p[2] + 40, "yellow glow beside the item: {p:?}");
+}
+
 #[test]
 fn inner_shadow_darkens_inside_the_lit_edge() {
     let mut d = doc();