The `method` text of `paint.editGradient` and two passages of
docs/mcp.md said a CMYK document writes RGB and Lab gradient stops in
CMYK. An export that converts colors to an RGB destination profile
converts them to that profile first, so in a CMYK document they stay
RGB and a Perceptual spot gradient with such stops is written as an
image with the spot warning. The texts now say so, and the test of RGB
stops in a CMYK document also checks the RGB destination case.
The method help of paint.editGradient and docs/mcp.md said a Perceptual
gradient with spot stops becomes an image in PDF unless every other stop
is paper white, CMYK or gray. PDF export checks each stop's color as it is
written: a CMYK document, or an export that converts colors to a CMYK
destination profile, writes RGB and Lab stops in CMYK, so the gradient
becomes a DeviceN shading. Both texts now say so, and a test covers the
CMYK document and CMYK destination cases.
A freeform gradient whose field has no points of its own takes its
colors from the stops, so spot-linked stops in it are written in
process colors too. The export now warns in that case, as it does for
the other gradients drawn as images.
A gradient of one spot ink's tints and paper white is written as a
Separation shading in that ink, with each white stop at 0% of it. A
white stop linked to a swatch that is not a spot color (a global White
swatch, for example) did not count as paper white. In an RGB document
the spot ink was then dropped: a Classic gradient was written in the
stops' own colors, and a Perceptual one was exported as an image in
process colors.
Such a stop now counts as paper white in the Separation and DeviceN
paths and in the checks that pick them, as an unlinked white stop does.
A stop linked to a white spot color is still a stop of that ink.
A Perceptual linear or radial gradient that mixes spot colors with each
other or with CMYK or gray stops was written as an image in process
colors. It is now written as a DeviceN shading of its inks, with the
stops on its Perceptual curve: at each one, the inks of the two stops on
either side are mixed at the weight where the two colors mixed in
display RGB have the OKLab lightness of the color on the curve.
- Gradient::ink_mixes gives the curve's stops as weights between stops,
under the same 4,096-stop limit as ink_tints.
- Perceptual gradients that mix a spot color with RGB or Lab stops,
dithered fills and freeform gradients stay images, and the warning
now names those cases.
A Perceptual linear or radial gradient was always written as an image,
so a gradient of spot ink tints lost its plate, and no warning named the
spot ink.
PDF export now writes a Perceptual gradient whose stops are tints of one
spot color (and paper white) as a Separation shading in that ink. Its
tints follow the gradient's curve: at each stop the renderer places on
the curve, the tint with the OKLab lightness of the color there.
Dithered fills, freeform gradients and Perceptual gradients that mix a
spot color with other colors are still images, and the export now warns
when such a gradient has stops linked to a spot swatch that its spot
colors are written in process colors.
- A radial gradient from a spot swatch to a CMYK color is written as a
DeviceN shading (ShadingType 3) of Yellow and the spot ink.
- A Lab spot color used as a flat fill and in a mixed gradient is
written as one Separation space with the Lab alternate, which the
DeviceN space names under /Colorants.
- docs/roadmap.md lists the gradients that still export without the
spot ink: mixed spot/process gradients in SVG and PDF gradients with
RGB or Lab stops. docs/target-app-parity.md also notes that a
Perceptual gradient is written to PDF as an image.
A linear or radial gradient whose stops mix a spot color with process
colors, or two spot colors, was written in process colors with a
warning. It is now written as a DeviceN shading of the process inks
its stops use and its spot inks, so each spot ink separates onto its
own plate. An off-center midpoint becomes a stop with the inks halfway
between its two stops. A gradient that mixes a spot color with RGB or
Lab colors is still written without the spot ink, with a warning that
says so.
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