Address CodeRabbit review: CMYK ink paths convert colours through the document profile (#3356)

Two places turned an RGB or Lab colour into ink with the built-in coated
CMYK instead of the document's embedded profile: the exact ink path's
tiles (render_tile runs on rayon workers, which never inherit a caller's
with_cmyk_space scope), e.g. a solid fill picked in RGB, and the split
path's stand-ins (fill and effect colours, converted on the calling thread
outside any scope). Both now enter cmyk_space(doc). A test with a synthetic
uncoated profile checks a solid fill and a Color Overlay get the profile's
inks; each half fails on its own without its fix.

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

Cargo.lock

@@ -4786,6 +4786,7 @@ name = "photocraft-compose"
 version = "0.13.0"
 dependencies = [
  "criterion",
+ "photocraft-cms",
  "photocraft-color",
  "photocraft-doc",
  "photocraft-geom",

crates/compose/Cargo.toml

@@ -21,6 +21,7 @@ rayon = { workspace = true }
 proptest = { workspace = true }
 criterion = { workspace = true }
 photocraft-paint = { workspace = true }
+photocraft-cms = { workspace = true }
 
 [[bench]]
 name = "compose"

crates/compose/src/cmyk.rs

@@ -18,7 +18,10 @@
 //!
 //! Buffers hold straight-alpha `[C, M, Y, K, A]` in 0..1 ink (0 = no ink).
 
+use std::sync::Arc;
+
 use photocraft_color::blend::BlendMode;
+use photocraft_color::convert::CmykSpace;
 use photocraft_color::{ColorMode, SampleType};
 use photocraft_doc::adjust::ToneSpace;
 use photocraft_doc::{Adjustment, Document, Knockout, Layer, LayerContent};
@@ -545,12 +548,15 @@ fn blend_into_fill(backdrop: &mut CmykBuffer, src: &CmykBuffer, l: &Layer, gamma
     }
 }
 
-fn render_tile(doc: &Document, rect: Rect, cx: &Ctx) -> CmykBuffer {
+/// One tile on ink values. `space` is the document's CMYK profile ([`super::cmyk_space`]): a
+/// colour given in RGB or Lab (a fill, say) becomes ink through it, and tiles run on worker
+/// threads, which don't inherit the caller's scope.
+fn render_tile(doc: &Document, rect: Rect, cx: &Ctx, space: Option<&Arc<CmykSpace>>) -> CmykBuffer {
     let mut b = CmykBuffer::transparent(rect);
     // Blends stay clipped to 0..1 whatever the depth: unclipped (HDR) blending would make
     // brightness above 1, i.e. negative ink. Set explicitly, since a tile can run on a thread
     // that is in the middle of an RGB composite of a 32-bit document.
-    super::in_blend_space(false, false, || composite_stack(&doc.layers, &mut b, cx));
+    photocraft_color::convert::with_cmyk_space(space, || super::in_blend_space(false, false, || composite_stack(&doc.layers, &mut b, cx)));
     b
 }
 
@@ -601,7 +607,8 @@ pub fn render_cmyk_tiled(doc: &Document, rect: Rect, tile: i32) -> Option<CmykBu
     if supports(doc) {
         let patterns = pattern::PreparedPatterns::new(&doc.patterns, pattern::PREPARED_PATTERN_BYTES).in_mode(doc.pixel_format().mode);
         let cx = Ctx::for_doc(doc, &patterns);
-        return Some(render_with(rect, tile, |t| render_tile(doc, t, &cx)));
+        let space = super::cmyk_space(doc);
+        return Some(render_with(rect, tile, |t| render_tile(doc, t, &cx, space.as_ref())));
     }
     if !split::supports(doc) {
         return None;
@@ -667,11 +674,12 @@ pub fn render_cmyk_bands<E>(doc: &Document, rect: Rect, band_rows: i32, mut sink
     }
     let patterns = pattern::PreparedPatterns::new(&doc.patterns, pattern::PREPARED_PATTERN_BYTES).in_mode(doc.pixel_format().mode);
     let cx = Ctx::for_doc(doc, &patterns);
+    let space = super::cmyk_space(doc);
     let rows = super::band_rows_for(rect.width(), band_rows);
     let mut y = rect.y0;
     while y < rect.y1 {
         let y1 = y.saturating_add(rows).min(rect.y1);
-        if let Err(e) = sink(render_with(Rect::new(rect.x0, y, rect.x1, y1), RENDER_TILE, |t| render_tile(doc, t, &cx))) {
+        if let Err(e) = sink(render_with(Rect::new(rect.x0, y, rect.x1, y1), RENDER_TILE, |t| render_tile(doc, t, &cx, space.as_ref()))) {
             return Some(Err(e));
         }
         y = y1;

crates/compose/src/cmyk_split.rs

@@ -262,11 +262,16 @@ fn stand_in_layer(l: &mut Layer, planes: Planes, depth: SampleType, canvas: Rect
 }
 
 /// `doc` as an RGB document carrying the `planes` inks' brightness.
+/// Colours given in RGB or Lab become ink through the document's own CMYK profile, as on the
+/// exact ink path.
 pub(super) fn stand_in(doc: &Document, planes: Planes) -> Document {
     let mut d = doc.clone();
     d.mode = ColorMode::Rgb;
     d.icc_profile = None;
-    d.layers.iter_mut().for_each(|l| stand_in_layer(l, planes, doc.depth, doc.bounds()));
+    let space = crate::cmyk_space(doc);
+    photocraft_color::convert::with_cmyk_space(space.as_ref(), || {
+        d.layers.iter_mut().for_each(|l| stand_in_layer(l, planes, doc.depth, doc.bounds()));
+    });
     d
 }
 

crates/compose/src/cmyk_tests.rs

@@ -1655,3 +1655,45 @@ fn flattening_keeps_exact_inks() {
     let stamp = crate::flatten_to_surface(&d, CMYKA8, None);
     assert_eq!(stamp.pixel(2, 0), vec![0.0, 0.0, 0.0, 1.0, q(0.4)]);
 }
+
+/// A colour given in RGB becomes ink through the document's own CMYK profile, not the built-in
+/// coated one, on both ink paths: a solid fill on the exact path (its tiles render on worker
+/// threads) and a Color Overlay on the split path (its stand-ins).
+#[test]
+fn rgb_colours_become_ink_through_the_document_profile() {
+    let profile = photocraft_cms::synth::cmyk_profile(&photocraft_cms::synth::CmykParams {
+        description: "Test Uncoated".into(),
+        tvi: [0.26, 0.26, 0.26, 0.3],
+        grid_a2b: 5,
+        grid_b2a: 9,
+        ..Default::default()
+    });
+    let bytes = profile.to_bytes();
+    let space = photocraft_color::convert::CmykSpace::for_profile(Some(&bytes));
+    assert!(space.is_some(), "a profile other than the built-in one");
+    let rgb = photocraft_color::Color { mode: ColorMode::Rgb, c: [0.2, 0.5, 0.8, 0.0], alpha: 1.0 };
+    let want = photocraft_color::convert::with_cmyk_space(space.as_ref(), || rgb.in_mode(ColorMode::Cmyk).c);
+    let builtin = rgb.in_mode(ColorMode::Cmyk).c;
+    assert!((0..4).any(|i| (want[i] - builtin[i]).abs() > 0.02), "the profiles differ: {want:?} {builtin:?}");
+    let check = |d: &Document, what: &str| {
+        let got = render_cmyk(d, d.bounds()).unwrap_or_else(|| panic!("supported"));
+        for p in &got.px {
+            assert!((0..4).all(|i| (p[i] - want[i]).abs() <= 1.0 / 255.0) && p[4] == 1.0, "{what}: {p:?}, want {want:?} (built-in {builtin:?})");
+        }
+    };
+
+    let mut exact = doc(8, 4);
+    exact.icc_profile = Some(bytes.clone());
+    exact.layers.push(Layer::new("fill", LayerContent::Fill(photocraft_doc::Fill::Solid(rgb))));
+    assert!(supports(&exact));
+    check(&exact, "solid fill");
+
+    let mut overlay = doc(8, 4);
+    overlay.icc_profile = Some(bytes);
+    let mut l = layer(&[(Rect::new(0, 0, 8, 4), [0.0, 0.0, 0.0, 1.0, 1.0])]);
+    l.effects.enabled = true;
+    l.effects.items.push(Effect::ColorOverlay { common: FxCommon::new(BlendMode::Normal, 1.0), color: rgb });
+    overlay.layers.push(l);
+    assert!(!supports(&overlay) && split::supports(&overlay));
+    check(&overlay, "colour overlay");
+}