M3.85: spot colours defined in Lab, with Spot Colors options for Lab values or CMYK equivalents

Colours gain a CIE Lab model (`Color::Lab {l,a,b}`, serde tag `lab`), handled through the
CMS (display, separation, conversions, gamut), tints (toward paper white), keep_model, harmonies,
recolouring, blends, Info and the Color panel. Swatch Options gets a Lab mode
(`swatch.edit {mode: "lab"}` / `{color: {l,a,b}}`), and colour params accept `{l,a,b}`.

Swatches panel → Spot Colors… (`ui.spotColors`, dialog `spotColors`) runs `swatch.spotOptions
{useLab}` (Document.spot_use_lab, default on): Lab spot colours show and separate from their Lab
values, or art linked to them takes their working-CMYK equivalents, as one undo step. PDF export
writes Lab spot inks as Separation spaces with a Lab alternate (tint function from paper white),
or a DeviceCMYK one with CMYK equivalents.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/colormgmt.rs

@@ -53,7 +53,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Convert Document Color Mode",
             ["File", "Document Color Mode"],
             None,
-            "{mode: \"cmyk\"|\"rgb\", intent?} set the document colour mode and convert every colour (art, symbols, swatches; swatch links kept) through the colour settings → {changed}",
+            "{mode: \"cmyk\"|\"rgb\", intent?} set the document colour mode and convert every colour (art, symbols, swatches; swatch links kept; Gray and Lab colours stay) through the colour settings → {changed}",
             has_doc,
             convert_mode
         ),
@@ -245,8 +245,9 @@ fn convert_mode(s: &mut Session, p: &Value) -> Result<Value> {
     let c = cms::active();
     let intent = intent_param(p, C)?.unwrap_or(c.settings().intent);
     let model = if mode == ColorMode::Cmyk { Model::Cmyk } else { Model::Rgb };
-    // Greys stay greys (they print on the black plate in either mode).
-    let conv = |col: &Color| if matches!(col, Color::Gray { .. }) { *col } else { c.convert(col, model, intent) };
+    // Greys stay greys (they print on the black plate in either mode); Lab colours (spot colour
+    // definitions) are device independent and fit either mode.
+    let conv = |col: &Color| if matches!(col, Color::Gray { .. } | Color::Lab { .. }) { *col } else { c.convert(col, model, intent) };
     let mut changed = 0usize;
     s.edit("Document Color Mode", |d, _| {
         d.color_mode = mode;
@@ -287,6 +288,7 @@ fn values(c: &Color) -> Vec<f32> {
         Color::Rgb { r, g, b } => vec![r, g, b],
         Color::Cmyk { c, m, y, k } => vec![c, m, y, k],
         Color::Gray { k } => vec![k],
+        Color::Lab { l, a, b } => vec![l, a, b],
     }
 }
 

crates/engine/src/cmd/mod.rs

@@ -253,7 +253,8 @@ pub fn matrix_param(p: &Value, key: &str) -> Option<Affine> {
     }
     Some(Affine::new(c))
 }
-/// A colour from `"#rrggbb"`, `[r,g,b]` (0..1), `{"c":..,"m":..,"y":..,"k":..}` or `{"gray":..}`.
+/// A colour from `"#rrggbb"`, `[r,g,b]` (0..1), `{"c":..,"m":..,"y":..,"k":..}`, `{"gray":..}` or
+/// `{"l":..,"a":..,"b":..}` (CIE Lab: L 0..100, a and b about −128..127).
 pub fn color_value(v: &Value) -> Option<Color> {
     match v {
         Value::String(s) => Color::from_hex(s),
@@ -267,6 +268,9 @@ pub fn color_value(v: &Value) -> Option<Color> {
                 let g = g.as_f64()?;
                 return Some(Color::gray(if g > 1.0 { g / 100.0 } else { g } as f32));
             }
+            if let (Some(l), Some(a), Some(b), None) = (o.get("l"), o.get("a"), o.get("b"), o.get("model")) {
+                return Some(Color::lab(l.as_f64()? as f32, a.as_f64()? as f32, b.as_f64()? as f32));
+            }
             serde_json::from_value(v.clone()).ok()
         }
         _ => None,

crates/engine/src/cmd/paint.rs

@@ -16,7 +16,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Fill",
             [],
             None,
-            "{color?: \"#rrggbb\"|[r,g,b]|{c,m,y,k}|{gray}, none?: true, swatch?: name (a global or spot colour stays linked, so swatch edits recolour it; a tint swatch links to its base at its tint; a gradient swatch is recorded as the gradient's swatch and fits each object, keeping its aspect; the built-in \"[Registration]\" prints on every plate), tint?: 0..100 (% of a global or spot `swatch`; default 100, or a tint swatch's own), gradient?: {kind?: linear|radial|freeform, stops?: [{offset 0..1, color, opacity? 0..1 (or 0..100), midpoint? 0.13..0.87, swatch?: global or spot colour (or tint) swatch the stop links to (its colour comes from the swatch), tint?: 0..100}] (at least 2; default white→black), angle?: deg, start?: [x,y], end?: [x,y] (the vector in document coordinates, both or neither; type objects keep it in text space), aspect?: % (radial; without start/end the gradient is placed on each object's bounds), swatch?: linked gradient swatch name}, item?: appearance item index|null (omitted: the Appearance panel's active item if it is a fill, else the top fill), ids?, focus?: true (false keeps the active proxy), keepModel?: false (in a CMYK document, RGB colours and gradient stops are stored as CMYK unless true; Gray stays Gray)} sets the selection's fill and the default (new art fits a gradient to itself)",
+            "{color?: \"#rrggbb\"|[r,g,b]|{c,m,y,k}|{gray}|{l,a,b} (CIE Lab), none?: true, swatch?: name (a global or spot colour stays linked, so swatch edits recolour it; a tint swatch links to its base at its tint; a gradient swatch is recorded as the gradient's swatch and fits each object, keeping its aspect; the built-in \"[Registration]\" prints on every plate), tint?: 0..100 (% of a global or spot `swatch`; default 100, or a tint swatch's own), gradient?: {kind?: linear|radial|freeform, stops?: [{offset 0..1, color, opacity? 0..1 (or 0..100), midpoint? 0.13..0.87, swatch?: global or spot colour (or tint) swatch the stop links to (its colour comes from the swatch), tint?: 0..100}] (at least 2; default white→black), angle?: deg, start?: [x,y], end?: [x,y] (the vector in document coordinates, both or neither; type objects keep it in text space), aspect?: % (radial; without start/end the gradient is placed on each object's bounds), swatch?: linked gradient swatch name}, item?: appearance item index|null (omitted: the Appearance panel's active item if it is a fill, else the top fill), ids?, focus?: true (false keeps the active proxy), keepModel?: false (in a CMYK document, RGB colours and gradient stops are stored as CMYK unless true; Gray stays Gray)} sets the selection's fill and the default (new art fits a gradient to itself)",
             has_doc,
             |s, p| set_paint(s, p, true)
         ),

crates/engine/src/cmd/swatch.rs

@@ -17,7 +17,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "New Swatch",
             ["Window", "Swatches"],
             None,
-            "{name?, color? | colors?: [colour] (one swatch each, in one undo step) | swatch? | gradient? | pattern?: name (default: the current fill), tint?: 0..100 (% of the global or spot `swatch`, or of the one the current fill links to), mode?: \"gray\"|\"rgb\"|\"hsb\"|\"cmyk\"|\"web\" (convert the colour), global?, spot? (a spot colour, always global), group?: colour group name (solid colours only; default: ungrouped)} save a colour, gradient or pattern as a swatch. A tint of a global or spot colour (below 100%, without mode, global or spot) becomes a tint swatch, \"Name 40%\", linked to its base: it follows edits to the base and applies as that tint of it. Names are unique (\"Sky 2\"); a colour's default name is its values (\"C=10 M=20 Y=30 K=0\", \"R=255 G=128 B=0\", \"Gray K=40\") → {name, names: [every new swatch]}",
+            "{name?, color? | colors?: [colour] (one swatch each, in one undo step) | swatch? | gradient? | pattern?: name (default: the current fill), tint?: 0..100 (% of the global or spot `swatch`, or of the one the current fill links to), mode?: \"gray\"|\"rgb\"|\"hsb\"|\"lab\"|\"cmyk\"|\"web\" (convert the colour; lab: CIE L*a*b*, how spot colours are usually defined), global?, spot? (a spot colour, always global), group?: colour group name (solid colours only; default: ungrouped)} save a colour, gradient or pattern as a swatch. A tint of a global or spot colour (below 100%, without mode, global or spot) becomes a tint swatch, \"Name 40%\", linked to its base: it follows edits to the base and applies as that tint of it. Names are unique (\"Sky 2\"); a colour's default name is its values (\"C=10 M=20 Y=30 K=0\", \"R=255 G=128 B=0\", \"Gray K=40\", \"L=55 a=60 b=40\") → {name, names: [every new swatch]}",
             has_doc,
             swatch_new
         ),
@@ -46,7 +46,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Swatch Options",
             ["Window", "Swatches"],
             None,
-            "{name, newName?, color?, mode?: \"gray\"|\"rgb\"|\"hsb\"|\"cmyk\"|\"web\" (convert the colour), global?, spot? (spot colours are always global), paint?: paint.setFill params ({color}, {gradient}, {swatch} or {pattern}) replacing the swatch's colour, gradient or pattern with one of the same kind} edit a swatch in any colour group, as one undo step. Fills, strokes, text, gradient stops and tint swatches linked to a global swatch take its new colour (at their own tint) and name; turning Global off unlinks them (they keep their colour). Colour, mode and spot apply to solid colours only; a tint swatch only takes a new name (edit its base) → {name, relinked: paints changed}",
+            "{name, newName?, color? (e.g. {l, a, b} for a Lab colour), mode?: \"gray\"|\"rgb\"|\"hsb\"|\"lab\"|\"cmyk\"|\"web\" (convert the colour), global?, spot? (spot colours are always global), paint?: paint.setFill params ({color}, {gradient}, {swatch} or {pattern}) replacing the swatch's colour, gradient or pattern with one of the same kind} edit a swatch in any colour group, as one undo step. Fills, strokes, text, gradient stops and tint swatches linked to a global swatch take its new colour (at their own tint) and name; turning Global off unlinks them (they keep their colour). Colour, mode and spot apply to solid colours only; a tint swatch only takes a new name (edit its base) → {name, relinked: paints changed}",
             has_doc,
             swatch_edit
         ),
@@ -113,6 +113,15 @@ pub fn specs() -> Vec<CommandSpec> {
             has_doc,
             swatch_sort_by_kind
         ),
+        cmd!(
+            "swatch.spotOptions",
+            "Spot Colors",
+            ["Window", "Swatches"],
+            None,
+            "{useLab?: bool (omitted: unchanged)} the document's Spot Colors options: spot colours defined in Lab show, print and export from their Lab values (true, the default: PDF Separation spaces get a Lab alternate) or from their working-CMYK equivalents (false: a DeviceCMYK alternate, matching older files). Art, gradient stops and tint swatches linked to Lab spot swatches take the chosen colour at their tint, as one undo step → {useLab, relinked: paints changed}",
+            has_doc,
+            swatch_spot_options
+        ),
     ]
 }
 
@@ -420,12 +429,13 @@ fn convert_to_mode(c: Color, mode: &str, cmd: &str) -> Result<Color> {
         "gray" | "grayscale" => to(Model::Gray),
         "rgb" | "hsb" => to(Model::Rgb),
         "cmyk" => to(Model::Cmyk),
+        "lab" => to(Model::Lab),
         "web" => {
             let snap = |v: f32| (v.clamp(0.0, 1.0) * 5.0).round() / 5.0;
             let [r, g, b] = to(Model::Rgb).to_rgb_uncalibrated();
             Color::rgb(snap(r), snap(g), snap(b))
         }
-        other => return Err(bad(cmd, format!("unknown mode `{other}` (gray, rgb, hsb, cmyk or web)"))),
+        other => return Err(bad(cmd, format!("unknown mode `{other}` (gray, rgb, hsb, lab, cmyk or web)"))),
     })
 }
 
@@ -434,7 +444,8 @@ struct Relink {
     from: String,
     /// The swatch's name after the edit.
     to: String,
-    /// The new colour of a global swatch (linked paints take it, at their tint).
+    /// The colour paints linked to the global swatch now show ([`Document::linked_color`]); they
+    /// take it at their tint.
     color: Option<Color>,
     /// false: drop the links (the swatch stopped being global); paints keep their colour.
     keep: bool,
@@ -518,7 +529,7 @@ fn swatch_edit(s: &mut Session, p: &Value) -> Result<Value> {
     let spot = bool_or(p, "spot", sw.spot);
     let global = spot || bool_or(p, "global", sw.global);
     let to = name_param(p, "newName").filter(|n| *n != name).map_or_else(|| name.clone(), |n| d.free_swatch_name(&n));
-    let relink = Relink { from: name.clone(), to: to.clone(), color: color.filter(|_| global), keep: global };
+    let relink = Relink { from: name.clone(), to: to.clone(), color: color.filter(|_| global).map(|c| d.linked_color(c, spot)), keep: global };
     let relinked = s.edit("Swatch Options", |d, _| {
         let w = d.swatch_mut(&name).ok_or_else(|| bad(C, format!("no swatch `{name}`")))?;
         w.name = to.clone();
@@ -673,7 +684,7 @@ fn swatch_merge(s: &mut Session, p: &Value) -> Result<Value> {
         return Err(bad(C, "give two or more swatches"));
     }
     let kept = d.swatch(keep).ok_or_else(|| bad(C, format!("no swatch `{keep}`")))?;
-    let (color, link) = (kept.paint.color().unwrap_or_default(), kept.global.then(|| keep.clone()));
+    let (color, link) = (d.linked_color(kept.paint.color().unwrap_or_default(), kept.spot), kept.global.then(|| keep.clone()));
     // Tints keep their tint (of the kept colour).
     let mut relink = |c: &mut Color, l: &mut Option<String>, t: &mut f32| {
         if !l.as_ref().is_some_and(|l| merged.contains(l)) {
@@ -724,3 +735,38 @@ fn swatch_sort_by_kind(s: &mut Session, _: &Value) -> Result<Value> {
     })?;
     ok()
 }
+
+fn swatch_spot_options(s: &mut Session, p: &Value) -> Result<Value> {
+    const C: &str = "swatch.spotOptions";
+    let was = s.doc()?.doc.spot_use_lab;
+    let use_lab = match p.get("useLab").filter(|v| !v.is_null()) {
+        Some(v) => v.as_bool().ok_or_else(|| bad(C, "`useLab` must be true or false"))?,
+        None => was,
+    };
+    if use_lab == was {
+        return Ok(json!({"useLab": use_lab, "relinked": 0}));
+    }
+    let (relinked, bases) = s.edit("Spot Colors", |d, _| {
+        d.spot_use_lab = use_lab;
+        // Each Lab spot swatch with the colour its linked paints now show.
+        let bases: Vec<(String, Color)> = d
+            .swatches_iter()
+            .filter(|w| w.spot && matches!(w.paint, Paint::Solid { color: Color::Lab { .. }, swatch: None, .. }))
+            .filter_map(|w| Some((w.name.clone(), d.global_color(&w.name)?)))
+            .collect();
+        let relinked = d.map_solid_paints(&mut follow_bases(&bases));
+        Ok((relinked, bases))
+    })?;
+    map_default_paints(s, &mut follow_bases(&bases));
+    Ok(json!({"useLab": use_lab, "relinked": relinked}))
+}
+
+/// Recolour the colours linked to the swatches of `bases` (name, colour) to that colour at their
+/// tint; true when a colour changed.
+fn follow_bases(bases: &[(String, Color)]) -> impl FnMut(&mut Color, &mut Option<String>, &mut f32) -> bool + '_ {
+    |c, link, tint| {
+        let Some((_, base)) = bases.iter().find(|(n, _)| link.as_ref() == Some(n)) else { return false };
+        let new = base.tinted(*tint);
+        std::mem::replace(c, new) != new
+    }
+}