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[PR #15283] Use Oklab for text and cursor contrast adjustments #30572

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opened 2026-01-31 09:41:37 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:41:37 +00:00
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Original Pull Request: https://github.com/microsoft/terminal/pull/15283

State: closed
Merged: Yes

Oklab by Björn Ottosson is a color space that has less irregularities
than the CIELAB color space used for ΔE2000. The distance metric for
Oklab (ΔEOK) is defined by CSS4 as the simple euclidian distance.
This allows us to drastically simplify the code needed to determine
a color that has enough contrast. The new implementation still lacks
proper gamut mapping, but that's another and less important issue.
I also made it so that text with the dim attribute gets adjusted just
like regular text, since this is an accessibility feature after all.

The new code is so much faster than the old code (12-125x) that I
dropped any caching code we had. While this increases the CPU overhead
when printing lots of indexed colors, the code is way less complex now.
"Increases" in this case however means something in the order of 15-60ns
per color change (as measured on my CPU). It's possible to further
improve the performance using explicit SIMD instructions, but I've
left that as a future improvement, since that will make the code quite
a bit more verbose and I didn't want to hinder the initial review.

Finally, these new routines are also used for ensuring that the
AtlasEngine cursors remains visible at all times.

Closes #9610

Validation Steps Performed

  • When adjustIndistinguishableColors is enabled
    colors are distinguishable ✅
  • An inverted cursor on top of a #7f7f7f foreground & background
    is still visible ✅
  • A colored cursor on top of a background with identical color
    is still visible ✅
  • Cursors on a transparent background are visible ✅
**Original Pull Request:** https://github.com/microsoft/terminal/pull/15283 **State:** closed **Merged:** Yes --- Oklab by Björn Ottosson is a color space that has less irregularities than the CIELAB color space used for ΔE2000. The distance metric for Oklab (ΔEOK) is defined by CSS4 as the simple euclidian distance. This allows us to drastically simplify the code needed to determine a color that has enough contrast. The new implementation still lacks proper gamut mapping, but that's another and less important issue. I also made it so that text with the dim attribute gets adjusted just like regular text, since this is an accessibility feature after all. The new code is so much faster than the old code (12-125x) that I dropped any caching code we had. While this increases the CPU overhead when printing lots of indexed colors, the code is way less complex now. "Increases" in this case however means something in the order of 15-60ns per color change (as measured on my CPU). It's possible to further improve the performance using explicit SIMD instructions, but I've left that as a future improvement, since that will make the code quite a bit more verbose and I didn't want to hinder the initial review. Finally, these new routines are also used for ensuring that the AtlasEngine cursors remains visible at all times. Closes #9610 ## Validation Steps Performed * When `adjustIndistinguishableColors` is enabled colors are distinguishable ✅ * An inverted cursor on top of a `#7f7f7f` foreground & background is still visible ✅ * A colored cursor on top of a background with identical color is still visible ✅ * Cursors on a transparent background are visible ✅
claunia added the pull-request label 2026-01-31 09:41:37 +00:00
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