Print color: Knockout Group and Isolate Blending as group attributes

Groups are pushed with Surface::push_group, so Knockout Group writes
/K true and Isolate Blending /I true, each on its own. File > Export PDF
no longer rasterizes knockout groups.

ROADMAP.md

@@ -127,7 +127,7 @@ DesignCraft aims at full Adobe InDesign parity — and to be better: faster, ope
 - Object Layer Options for placed PDFs (`object.pdfLayers`, `object.layerOptions`, Object ▸ Object Layer Options…): the file's optional-content layers listed and shown or hidden per frame on screen; in exported PDFs such graphics go out as 300 ppi images of their visible layers.
 - Effects: Inner Glow (edge or centre), Bevel and Emboss (inner bevel lit from the light angle), Satin (`object.innerGlow`, `object.bevel`, `object.satin`); PDF export now keeps soft effects: objects with shadows, glows, feathers, bevels or satin go out as 300 ppi transparent images of their appearance (threaded text frames excepted).
 - Directional Feather (`object.directionalFeather {widths: [top, left, bottom, right]}`): each side fades over its own width.
-- View ▸ Flattener Preview (`view.flattenerPreview`): objects involving transparency highlighted in red; knockout groups export as images (PDF output has no knockout groups).
+- View ▸ Flattener Preview (`view.flattenerPreview`): objects involving transparency highlighted in red; PDF export writes Knockout Group as a knockout transparency group (`/K true`) and Isolate Blending as `/I true`.
 - Live captions (`object.caption {live: true}`, Object ▸ Captions ▸ Generate Live Caption): the caption text is re-filled from the source object's metadata after every edit (same undo step).
 - Style Export Tagging (`style.exportTag`, Paragraph Style Options ▸ Export Tagging): paragraph and character styles choose their HTML element and class in EPUB/HTML.
 - Tagged Text: export (`file.exportText {format: "tagged"}`) and place (detected by its header; ASCII, UTF-8 or UTF-16) with paragraph and character styles, font, typeface and size, and `<0x…>` characters.

crates/engine/src/cmd/export.rs

@@ -513,9 +513,7 @@ fn threaded(d: &designcraft_doc::Document, it: &designcraft_doc::Item) -> bool {
 /// Soft effects other than the gradient feather (which PDF export draws itself).
 fn raster_effects(it: &designcraft_doc::Item) -> bool {
     let e = &it.effects;
-    // Knockout groups too: PDF output here has no knockout transparency groups.
-    it.knockout
-        || e.drop_shadow.on
+    e.drop_shadow.on
         || e.feather > 0.0
         || e.inner_shadow.on
         || e.outer_glow.on
@@ -795,7 +793,7 @@ fn export_pdf(s: &mut Session, p: &Value) -> Result<Value> {
         }
     }
     if fx_count > 0 {
-        r.warnings.push(format!("{fx_count} object(s) with soft effects (shadows, glows, feathers, bevels) or knockout groups exported as images"));
+        r.warnings.push(format!("{fx_count} object(s) with soft effects (shadows, glows, feathers, bevels) exported as images"));
     }
     if layer_count > 0 {
         r.warnings.push(format!("{layer_count} placed PDF(s) with hidden layers exported as images"));

crates/engine/src/cmd/object.rs

@@ -4195,13 +4195,14 @@ mod fitting_tests {
         let df = shot(&s);
         assert!(df.pixel(102, 200)[0] > 200, "left edge faded to paper: {:?}", df.pixel(102, 200));
         assert_eq!(df.pixel(298, 200), plain.pixel(298, 200), "right edge untouched");
-        // A knockout group exports as an image too.
+        // A knockout group stays vector, as a knockout transparency group.
         let other = s.execute("frame.create", &json!({"rect": [400, 100, 450, 150]})).unwrap()["id"].clone();
         let other2 = s.execute("frame.create", &json!({"rect": [420, 120, 470, 170]})).unwrap()["id"].clone();
         let g = s.execute("object.group", &json!({"ids": [other, other2]})).unwrap()["id"].clone();
         s.execute("object.transparencyGroup", &json!({"ids": [g], "knockout": true})).unwrap();
         let r = s.execute("file.exportPdf", &json!({})).unwrap();
-        assert!(r["warnings"].as_array().unwrap().iter().any(|w| w.as_str().unwrap().contains("2 object(s)")), "{r}");
+        assert!(r["warnings"].as_array().unwrap().iter().any(|w| w.as_str().unwrap().contains("1 object(s)")), "{r}");
+        assert!(String::from_utf8_lossy(&super::super::file::base64_decode(r["base64"].as_str().unwrap())).contains("/K true"));
         // PDF export carries effects (as an image of the object).
         let r = s.execute("file.exportPdf", &json!({})).unwrap();
         assert!(r["warnings"].as_array().unwrap().iter().any(|w| w.as_str().unwrap().contains("soft effects")), "{r}");

crates/pdf/src/export.rs

@@ -749,11 +749,10 @@ impl Exporter<'_> {
         n
     }
 
-    /// Isolate Blending / Knockout groups: an isolated transparency group (knockout is drawn
-    /// isolated too).
+    /// Isolate Blending / Knockout Group: a transparency group with `/I` and `/K` as set.
     fn push_isolation(s: &mut Surface, it: &Item) -> usize {
         if it.isolate || it.knockout {
-            s.push_isolated();
+            s.push_group(krilla::blend::GroupOptions { isolated: it.isolate, knockout: it.knockout });
             1
         } else {
             0

crates/pdf/src/print_tests.rs

@@ -240,3 +240,38 @@ fn ruby_overprint_fill_is_written() {
     assert_eq!(overprint_states(&r.bytes), [(true, false, 1)]);
     assert!(!r.warnings.iter().any(|w| w.contains("overprint")), "{:?}", r.warnings);
 }
+
+/// Knockout Group writes `/K true` and Isolate Blending `/I true`, each on its own.
+#[test]
+fn knockout_and_isolation_are_group_attributes() {
+    let grouped = |knockout: bool, isolate: bool| {
+        let mut d = Document::new(&NewDocument::default());
+        let lid = d.default_layer();
+        let child = |d: &mut Document, r: Rect, swatch: &str| {
+            let mut b = Item::new(ItemId(d.alloc()), lid, designcraft_doc::Shape::Rectangle, designcraft_geom::shapes::rectangle(r));
+            b.fill = Fill::swatch(swatch);
+            std::sync::Arc::new(b)
+        };
+        let items = vec![
+            child(&mut d, Rect::new(36.0, 36.0, 136.0, 136.0), "C=100 M=0 Y=0 K=0"),
+            child(&mut d, Rect::new(86.0, 86.0, 186.0, 186.0), "C=0 M=100 Y=0 K=0"),
+        ];
+        let mut g = Item::new(
+            ItemId(d.alloc()),
+            lid,
+            designcraft_doc::Shape::Group,
+            designcraft_geom::shapes::rectangle(Rect::new(36.0, 36.0, 186.0, 186.0)),
+        );
+        g.content = designcraft_doc::Content::Group { items };
+        g.knockout = knockout;
+        g.isolate = isolate;
+        d.insert_item(SpreadRef::Doc(0), g, None).unwrap();
+        form_groups(&exported(&d))
+    };
+    let attributes =
+        |groups: Vec<(Option<String>, bool, bool)>| groups.into_iter().map(|(_, i, k)| (i, k)).filter(|ik| *ik != (false, false)).collect::<Vec<_>>();
+    assert_eq!(attributes(grouped(true, false)), [(false, true)]);
+    assert_eq!(attributes(grouped(false, true)), [(true, false)]);
+    assert_eq!(attributes(grouped(true, true)), [(true, true)]);
+    assert_eq!(attributes(grouped(false, false)), []);
+}

docs/target-app-parity.md

@@ -389,7 +389,7 @@ It is evidence of breadth: each item exists. It is not a claim of InDesign-level
 - Object Layer Options for placed PDFs (`object.pdfLayers`, `object.layerOptions`, Object ▸ Object Layer Options…): the file's optional-content layers listed and shown or hidden per frame on screen; in exported PDFs such graphics go out as 300 ppi images of their visible layers.
 - Effects: Inner Glow (edge or centre), Bevel and Emboss (inner bevel lit from the light angle), Satin (`object.innerGlow`, `object.bevel`, `object.satin`); PDF export now keeps soft effects: objects with shadows, glows, feathers, bevels or satin go out as 300 ppi transparent images of their appearance (threaded text frames excepted).
 - Directional Feather (`object.directionalFeather {widths: [top, left, bottom, right]}`): each side fades over its own width.
-- View ▸ Flattener Preview (`view.flattenerPreview`): objects involving transparency highlighted in red; knockout groups export as images (PDF output has no knockout groups).
+- View ▸ Flattener Preview (`view.flattenerPreview`): objects involving transparency highlighted in red; PDF export writes Knockout Group as a knockout transparency group (`/K true`) and Isolate Blending as `/I true`.
 - Live captions (`object.caption {live: true}`, Object ▸ Captions ▸ Generate Live Caption): the caption text is re-filled from the source object's metadata after every edit (same undo step).
 - Style Export Tagging (`style.exportTag`, Paragraph Style Options ▸ Export Tagging): paragraph and character styles choose their HTML element and class in EPUB/HTML.
 - Tagged Text: export (`file.exportText {format: "tagged"}`) and place (detected by its header; ASCII, UTF-8 or UTF-16) with paragraph and character styles, font, typeface and size, and `<0x…>` characters.