Gradients: freeform points that share a color model mix in that model

The canvas, the gradient chips and the SVG, PDF, EPS and EMF writers mixed
freeform points in display RGB, while Object > Expand and Create Gradient
Mesh mixed them in the model the points share. Points that are all CMYK,
Gray, Lab or RGB now mix in that model in those places too. Points in
different models mix as before: in display RGB, and on ink planes as the
inks of each point.

This changes how existing art looks:

- CMYK and Lab points. With the default Generic CMYK working space and no
  ink planes, halfway between C100 and K100 the canvas drew (17, 106, 139)
  and now draws (54, 118, 143).
- RGB points in a working RGB space other than sRGB mix in that space.
- On ink planes (a CMYK document that shows transparency), RGB and Lab
  points mix first and then separate.

Gray mixes keep their values, and CMYK and Gray points on ink planes draw
as before. RGB points in an sRGB working space draw as before except on
ink planes.

- PDF and EPS write a gradient whose points are all CMYK, or all Gray in a
  CMYK file, as a CMYK image. PDF's Output settings convert it as they
  convert any CMYK image.
- Darkening applies to the points before they mix.
- With Appearance of Black set to Rich, the canvas mixes a gradient with a
  pure CMYK black point in display RGB, and the point fades from RGB black.

docs/mcp.md

@@ -803,7 +803,8 @@ A `security` password encrypts the file (RC4 40-bit at PDF 1.3, RC4 128-bit at 1
 1.7 and 2.0) with its permissions; either password opens it (`document.open {password}`), and a password with PDF/A or PDF/X is refused.
 Pattern fills and strokes are written as their tiles clipped to the area they paint (a stroke's outline, with its
 dashes, caps, profile, arrowheads and alignment), and freeform gradients as an image of their colour field at the
-document's raster effects resolution, clipped the same way.
+document's raster effects resolution, clipped the same way (a CMYK image when every point is CMYK or, in a CMYK
+document, every point is Gray; the Output settings convert it as they convert any CMYK image).
 `createLayers` writes each layer and sublayer (template layers are left out) as a PDF layer, an optional content group
 named as the layer and listed under its parent layer's: hidden layers are off (their art is written, for the reader to
 show), non-printing ones have `/PrintState /OFF` and locked ones are locked. It needs PDF 1.5 or later (at 1.4 it
@@ -1017,7 +1018,10 @@ line?}`, `setPoint {index?, …}`, `deletePoint {index?}`, `addLine {points}`, `
 `selectPoint {index|null}` edit them (`index` defaults to the selected point; each edit is one undo step). The color
 of a point colored along the stops, of a point `splitLine` adds and of a point `addPoint` adds without `color` is a mix
 of the colors around it (the two stops, the line's two points, or all the points) in the color model those colors
-share, so CMYK stops and points give CMYK points. With the
+share, so CMYK stops and points give CMYK points. Points that are all CMYK, Gray, Lab or RGB mix in that model on the
+canvas, in the swatch and Fill and Stroke chips, and in the SVG, PDF, EPS and EMF writers; points in different models
+mix in display RGB (on the canvas in a CMYK document that shows transparency, as the inks of each point). With
+Appearance of Black set to Rich, the canvas mixes points that include pure CMYK black in display RGB. With the
 Gradient tool on a freeform gradient a click on a point selects it (drag to move it), a click on a line adds a point
 on it, a click elsewhere on the art adds a point (in Lines mode joined to the selected one), and Delete removes the
 selected point:
@@ -5039,7 +5043,8 @@ without `useArtboards` (no central file when no art shows). `level: 3` (default)
 shadings and masks transparent image pixels out; `level: 2` writes gradients as bands of colour (as does
 `compatibleGradients`) and transparent pixels white. Type is always glyph outlines, so no fonts are needed (`embedFonts`
 is accepted); spot colours are Separation colour spaces, and overprinting fills and strokes overprint unless
-`overprints: "discard"`. RGB documents are written in CMYK unless `cmykPostScript: false`. When the file would hold an
+`overprints: "discard"`. RGB documents are written in CMYK unless `cmykPostScript: false`. A freeform gradient is
+written as an image, in CMYK when every point is CMYK or when every point is Gray in a file written in CMYK. When the file would hold an
 image that can't be decoded, the image is left out, and `warnings` carries "an image couldn't be decoded and is missing
 from the picture" once for all such images.
 Colorized grayscale and 1-bit images use their process or spot ink; the flattener leaves them alone unless they have opacity, a blending mode, an opacity mask or effects, or overlap other transparent art. Binary coverage leaves underlying art untouched. For a grayscale image, Level 3 leaves white (zero-coverage) pixels out, Level 2 writes them white, and gray midtones are written over white at both levels.

docs/target-app-parity.md

@@ -1192,7 +1192,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - The stop popover a double-click on a stop opens (the Gradient tool's annotator or the Gradient panel) has an eyedropper beside its Color and Swatches tabs: it closes the popover and samples the next colour clicked on the art into the stop, as the Gradient panel's eyedropper does (#4681).
     Cmd/Ctrl-click on the Gradient panel's Gradient Fill box or on the Tools panel's Gradient button resets the gradient of the active Fill or Stroke to the linear White, Black gradient, as one undo step ([Default keyboard shortcuts](https://web.archive.org/web/20260726060015/https://helpx.adobe.com/illustrator/using/default-keyboard-shortcuts.html)).
     With a gradient stop or a freeform gradient point selected, Alt-clicking a color swatch in the Swatches panel recolors it instead of the inactive Fill or Stroke.
-  - **Freeform gradient colors in their own model:** Object ▸ Expand and Object ▸ Create Gradient Mesh (`object.mesh.create`) mix a freeform gradient's points in the color model they share: points of C50 M20 Y0 K10 give mesh points of C50 M20 Y0 K10, and RGB points keep their values in a working RGB space other than sRGB. Points in different models mix in display RGB, and a CMYK document stores the result as CMYK through the color settings. Points colored along CMYK stops (`paint.editGradient {stops}`, or a CMYK gradient switched to freeform) are CMYK, and so are a point `paint.freeform.splitLine` adds between CMYK points and a point `paint.freeform.addPoint` adds without `color` to CMYK points. Public reference: [Gradients](https://web.archive.org/web/20250714042311/https://helpx.adobe.com/illustrator/using/gradients.html) and [Meshes](https://web.archive.org/web/20250812201019/https://helpx.adobe.com/illustrator/using/meshes.html), which do not state how colors in different models mix; the rule is VectorCraft's own.
+  - **Freeform gradient colors in their own model:** Object ▸ Expand and Object ▸ Create Gradient Mesh (`object.mesh.create`) mix a freeform gradient's points in the color model they share: points of C50 M20 Y0 K10 give mesh points of C50 M20 Y0 K10, and RGB points keep their values in a working RGB space other than sRGB. The canvas, the gradient chips and the SVG, PDF, EPS and EMF writers mix the points in that model too. PDF and EPS write a gradient whose points are all CMYK, or all Gray in a CMYK file, as a CMYK image, which PDF's Output settings convert as they convert any CMYK image. Points in different models mix in display RGB (on the canvas in a CMYK document that shows transparency, as the inks of each point), and a CMYK document stores the result of Expand as CMYK through the color settings. Points colored along CMYK stops (`paint.editGradient {stops}`, or a CMYK gradient switched to freeform) are CMYK, and so are a point `paint.freeform.splitLine` adds between CMYK points and a point `paint.freeform.addPoint` adds without `color` to CMYK points. Public reference: [Gradients](https://web.archive.org/web/20250714042311/https://helpx.adobe.com/illustrator/using/gradients.html) and [Meshes](https://web.archive.org/web/20250812201019/https://helpx.adobe.com/illustrator/using/meshes.html), which do not state how colors in different models mix; the rule is VectorCraft's own.
   - **Strokes:** one stroke-geometry module shared by the canvas, SVG, PDF and Outline Stroke; dotted lines (zero-length dashes draw dots or squares); arrowheads with hollow outlines, tip-on-end or extend-past-end alignment and one opacity for line and head. SVG and PDF export arrowheads, width profiles, brushes and aligned strokes exactly as the canvas draws them; Outline Stroke and the live Outline Stroke effect outline every stroke item as drawn (dashes, heads, profiles, alignment); dashes can be fitted to corners and path ends; width profiles carry through dashes, and their corners take the join. The Stroke panel edits type's character strokes, follows the stroke units (its weight presets are round values in that unit: `0.25 mm`, `0.0625 in`, `1 px`, #426; fields show four decimals in mm, cm and inches, three in points), shows mixed values blank and opens from the Control bar. A width profile library, thirty more arrowheads, and Width Point Edit with multi-select and discontinuous points. Visual bounds and clicks cover the whole painted stroke. Scale Strokes & Effects, Scale Corners and Use Preview Bounds work everywhere, and new art inherits stroke options, a graphic style or the whole last appearance.
   - **Brushes (part of #852):** double-clicking a brush in the Brushes panel (or the panel menu's Brush Options…) opens Calligraphic Brush Options (Name; Angle, Roundness and Size, each Fixed, Random, Pressure, Tilt, Bearing or Rotation with its Variation; live previews of the nib and of a light–heavy–light stroke) or Bristle Brush Options (Shape and the bristle sliders); OK edits the brush and every stroke painted with it. The Paintbrush records the pen pressure along each stroke (kept with the path, saved, and joined when a stroke continues a path); a Calligraphic value on Pressure goes from value − variation at the lightest pressure to value + variation at the heaviest, on the canvas and in SVG, PDF and the other exports. Brushes saved before keep their look. Scatter Brush Options (Size, Spacing, Scatter and Rotation, each Fixed, Random between two values, Pressure from the first at the lightest pressure to the second at the heaviest, Tilt, Bearing or Rotation; Rotation relative to Page or Path), Art Brush Options (Width, Scale Proportionately, Stretch to Fit Stroke Length or Stretch Between Guides with the guides' start and end, the four Directions, Flip Along and Across) and Pattern Brush Options (Scale, Spacing, the five tiles shown, Flip Along and Across, Stretch to fit, Add space to fit or Approximate path) each have Colorization (None, Tints, Tints and Shades, Hue Shift with its Key Color picked from the art's colours) and a live stroke preview; values from files and commands are clamped to their ranges. Still to come: the Art brush's Overlap, Stylus Wheel, and the pen's tilt, bearing and rotation on Windows, native Wayland and the web.
     Under Tints and Tints and Shades, art in black ink alone goes by its ink amount, and a process or gray stroke color's tints and shades stay in that color's model; these are VectorCraft's own rules.