CSS Color Level 4, New Color Spaces: Draft 1.2 (sass#3426)

proposal/color-4-new-spaces.changes.md

@@ -1,3 +1,80 @@
+## Draft 1.2
+
+* Clamp `hsl` saturation & lightness when generating `hsl` colors, and gamut-map
+  when converting colors into either `hsl` or `hwb`, since those spaces cannot
+  properly maintain out-of-gamut color values.
+
+* Ensure that color space names are unquoted strings, and compared insensitive
+  to case.
+
+* Remove support for custom or unknown color spaces. There are too many open
+  questions in the CSS spec, as browsers have not started to implement this
+  feature yet.
+
+* Remove channel indexing, and syntax to access channels by index, since all
+  known color channels have names.
+
+* Allow channel adjustment values to be out-of-gamut, and then normalize the
+  resulting channel values. This allows more flexibility, while ensuring that
+  `hsl` or `hwb` clamp out-of-gamut results.
+
+* Channel clamping and scaling for `hsl` and `hwb` colors is handled in the
+  normalization process, rather than the individual functions. This also allows
+  it to happen when normalizing the results of color manipulation.
+
+* Throw an error in the color component parsing procedure if a known color space
+  is one of the components, and has a function of it's own (e.g. `rgb` or
+  `oklch`). Only custom color spaces and predefined spaces can be defined using
+  the `color(<space> <channels>)` syntax.
+
+* Add missing `$weight` to the `color.invert()` signature, and return early
+  when the specified weight is `0%` or `100%`.
+
+* Update the color interpolation procedure handling of `weight` values to error
+  when `weight` is outside the `[0,1]` range, and return early when `weight` is
+  equal to 0 or 1.
+
+* For backwards compatibility, the `color.change()`, `color.scale()`, and
+  `color.adjust()` functions allow manipulating legacy colors in any legacy
+  space, if the `$space` argument is not explicitly set.
+
+* Remove `in` prefix from the color interpolation method syntax, since the Sass
+  function syntax is already explicit about which parameter is where.
+
+* `color.invert()` throws an error when `$weight` would require mixing in an
+  invalid `color.mix()` _interpolation color space_.
+
+* Allow scaling channels with a non-0 minimum value, such as the `a` and `b`
+  channels in `lab()`/`oklab()`.
+
+* Ensure that percentage and percentage-mapped number values are normalized
+  before they are added together in `color.adjust()`.
+
+* Clarify that channel values are stored as raw doubles, and add/remove units
+  as necessary for normalization/serialization.
+
+* Legacy colors with missing channels are serialized using the non-legacy
+  serialization logic. When converting colors into legacy spaces with
+  `color.to-space()`, all missing components are replaced with `0` for better
+  legacy output.
+
+* `color.channel()` returns `0` when the channel value is missing, rather than
+  throwing an error.
+
+* Added `color.is-missing($color, $channel)` to inspect if a channel is set to
+  'none' (e.g. missing).
+
+* Legacy colors using a space-separated syntax with special number values that
+  are not adjacent to a `/` symbol are emitted using the legacy
+  (comma-separated) CSS syntax. For example:
+
+  * `hsl(20deg 5% var(--foo))` emits `hsl(20deg, 5%, var(--foo))`.
+
+  * `hsl(20deg var(--foo) 5% / 0.5)` emits `hsl(20deg, var(--foo), 5%, 0.5)`.
+
+  * `hsl(20deg 5% var(--foo) / 0.5)` emits `hsl(20deg 5% var(--foo)/0.5)`
+    since the special value is adjacent to the slash.
+
 ## Draft 1.1
 
 * Expand the summary section to describe more of the proposal.