Brush: CMYK foreground paints the picked inks into a CMYK document (#4344) (#4347)

* Color Picker: CMYK foreground fills a CMYK document with the picked inks (#4196)

The tool colours are stored as sRGB, so a colour picked as CMYK 100/0/0/0
(outside sRGB) came back as 100/28/0/17 when a CMYK document was filled.
tools.setColors now takes foregroundCmyk/backgroundCmyk, the picker sends
the entered inks, and Edit > Fill (and the fill keys) write them as they
are into a CMYK target. Fill also enters the document's CMYK profile.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Brush and Pencil paint a CMYK foreground with the picked inks in a CMYK document (#4344)

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>

crates/engine/src/brush_cmds.rs

@@ -204,6 +204,7 @@ pub fn resolve_brush(s: &Session, p: &Value, cmd: &str) -> Result<BrushSettings>
         b.smoothing.amount = v.clamp(0.0, 1.0);
     }
     b.color = color(p.get("color"), s.tools.foreground);
+    b.color_cmyk = s.tools.picked_cmyk([b.color[0], b.color[1], b.color[2]]).map(|k| ([b.color[0], b.color[1], b.color[2]], k));
     b.background = s.tools.background;
     b.erase = flag(p, "erase", false);
     b.seed = match p.get("seed").and_then(Value::as_u64) {
@@ -367,6 +368,7 @@ fn block_brush(b: BrushSettings, p: &Value) -> Result<BrushSettings> {
         pressure_opacity: false,
         spacing: 0.25,
         color: b.color,
+        color_cmyk: b.color_cmyk,
         background: b.background,
         erase: b.erase,
         smoothing: b.smoothing,

crates/engine/src/brush_cmds/tests.rs

@@ -883,3 +883,21 @@ fn clear_mode_erases_with_the_brush_or_pencil() {
         assert_eq!(s.active().unwrap().history.undo_label(), Some(label), "{cmd}");
     }
 }
+
+/// #4344: a foreground picked as CMYK 100/0/0/0 is painted into a CMYK document as those inks by
+/// the Brush and the Pencil, not as whatever its sRGB stand-in converts back to (100/28/0/17).
+#[test]
+fn brush_and_pencil_paint_a_cmyk_pick_with_the_picked_inks() {
+    let cyan = [1.0f32, 0.0, 0.0, 0.0];
+    for cmd in ["paint.stroke", "paint.pencil"] {
+        let mut s = session(16, 16);
+        s.execute("image.mode.cmyk", json!({})).unwrap();
+        let rgb = photocraft_color::convert::cmyk_to_rgb(cyan).map(|c| c.clamp(0.0, 1.0));
+        s.execute("tools.setColors", json!({"foreground": rgb, "foregroundCmyk": cyan})).unwrap();
+        s.execute(cmd, json!({"points": [[8.0, 8.0]], "size": 6.0, "hardness": 1.0})).unwrap();
+        let st = s.active().unwrap();
+        let surf = st.doc.layer(st.active_layer.unwrap()).unwrap().surface().unwrap();
+        let got: Vec<f32> = surf.read_region(Rect::new(8, 8, 9, 9)).into_iter().take(4).collect();
+        assert!(got.iter().zip(cyan).all(|(a, b)| (a - b).abs() < 0.02), "{cmd}: {got:?}");
+    }
+}

crates/paint/src/brush.rs

@@ -486,6 +486,11 @@ pub struct BrushSettings {
     pub pressure_opacity: bool,
     /// Straight RGBA colour (display RGB). Commands fill it from the foreground colour.
     pub color: [f32; 4],
+    /// The inks `color` was picked as (its sRGB colour, the CMYK values), for a CMYK target: the
+    /// stroke paints exactly these, since an sRGB round trip does not give them back (#4344).
+    /// Only valid while `color` is that sRGB colour; ignored with Color Dynamics.
+    #[serde(skip)]
+    pub color_cmyk: Option<([f32; 3], [f32; 4])>,
     /// Background colour for Color Dynamics' foreground/background jitter.
     pub background: [f32; 4],
     /// Erase instead of paint.
@@ -545,6 +550,7 @@ impl Default for BrushSettings {
             pressure_size: true,
             pressure_opacity: false,
             color: [0.0, 0.0, 0.0, 1.0],
+            color_cmyk: None,
             background: [1.0, 1.0, 1.0, 1.0],
             erase: false,
             mode: BlendMode::Normal,

crates/paint/src/render.rs

@@ -10,7 +10,7 @@
 use std::collections::{HashMap, HashSet};
 use std::sync::Arc;
 
-use photocraft_color::{BlendMode, PixelFormat, SampleType};
+use photocraft_color::{BlendMode, ColorMode, PixelFormat, SampleType};
 use photocraft_geom::Rect;
 use photocraft_raster::{Surface, from_rgba_into, to_rgba};
 
@@ -966,6 +966,12 @@ impl StrokeRenderer {
         let opacity = b.opacity.clamp(0.0, 1.0);
         let mut src = [0.0f32; 8];
         from_rgba_into(&fmt, b.color, &mut src);
+        // A colour picked as CMYK paints its inks as they are in a CMYK target (#4344).
+        if let (ColorMode::Cmyk, Some((rgb, inks))) = (fmt.mode, b.color_cmyk)
+            && rgb == [b.color[0], b.color[1], b.color[2]]
+        {
+            src[..4].copy_from_slice(&inks);
+        }
         if let Some(a) = a_idx {
             src[a] = b.color[3];
         }