From 31037c11d5638f828e7dda670f59339d4801018d Mon Sep 17 00:00:00 2001 From: facelessuser Date: Thu, 29 Jan 2026 22:30:52 -0700 Subject: [PATCH 1/3] [css-color-4] Correction to ray trace to avoid throwing off our intersection calculation The suggested fix via https://github.com/w3c/csswg-drafts/issues/10579#issuecomment-3815362986 was not the ideal fix and artificially limited `tnear`. This is a numerical instability issue and should be addressed as such by using an epsilon compare to prevent rays that are too small. Related #10579 --- css-color-4/Overview.bs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs index b8757467da33..fa4f016b5a20 100644 --- a/css-color-4/Overview.bs +++ b/css-color-4/Overview.bs @@ -6135,7 +6135,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping

let |d| be |b| - |a|

let |direction|[i] be |d|

-

if (d != 0): +

if abs(|d|) < 1E-15

• let |inv_d| be 1 / |d|
• let |t1| be (|bmin|[i] - |a|) * |inv_d|
@@ -6165,7 +6165,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping

-

if (|tnear| > 10) +

if |tnear| is infinite (or matches the initial very large value)

• return INTERSECTION NOT FOUND

From db955e104b2aa2869f172dfadbe0d9647a4e1686 Mon Sep 17 00:00:00 2001 From: facelessuser Date: Sun, 1 Feb 2026 21:16:55 -0700 Subject: [PATCH 2/3] A little more buffer --- css-color-4/Overview.bs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs index fa4f016b5a20..513d42fe1a60 100644 --- a/css-color-4/Overview.bs +++ b/css-color-4/Overview.bs @@ -6135,7 +6135,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping

let |d| be |b| - |a|

let |direction|[i] be |d|

-

if abs(|d|) < 1E-15 +

if abs(|d|) < 1E-12

• let |inv_d| be 1 / |d|
• let |t1| be (|bmin|[i] - |a|) * |inv_d|
From b9863d39c02e67de9071ef03bce7e383d6e515e1 Mon Sep 17 00:00:00 2001 From: facelessuser Date: Mon, 2 Feb 2026 07:55:40 -0700 Subject: [PATCH 3/3] Match the flow CSS - Return unbounded colors - Return black/white if SDR lightness is exceeded. - Then if color is out of gamut continue chroma reduction --- css-color-4/Overview.bs | 74 ++++++++++++++++++++++------------------- 1 file changed, 39 insertions(+), 35 deletions(-) diff --git a/css-color-4/Overview.bs b/css-color-4/Overview.bs index 513d42fe1a60..34261b7de22d 100644 --- a/css-color-4/Overview.bs +++ b/css-color-4/Overview.bs @@ -6052,9 +6052,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping
-
1. if |origin| is in gamut for |destination|, - convert |origin| to |destination| and return it as the gamut mapped color -
+
2. if |destination| has no gamut limits (XYZ-D65, XYZ-D50, Lab, LCH, Oklab, OkLCh) convert |origin| to |destination| and return it as the gamut mapped color
3. let |origin_OkLCh| be |origin| converted from |origin color space| to the OkLCh color space
@@ -6071,45 +6069,51 @@ Sample Pseudocode for the Ray Trace Gamut Mapping
4. let |origin_rgb| be |origin_OkLCh| converted to the linear-light form of |destination|
-
5. let |low| be 1E-6 ¹
-
6. let |high| be 1.0 - |low| ²
-
7. let |last| be |origin_rgb|
-
8. for (i=0; i<4; i++) + +
9. if |origin_rgb| is not in gamut
   -
   • if (i > 0) + +
   • let |low| be 0.0 + 1E-6 ¹
   +
   • let |high| be 1.0 - 1E-6 ²
   +
   • let |last| be |origin_rgb|
   +
   • for (i=0; i<4; i++)
     -
     • let |current_OkLCh| be |origin_rgb| converted to OkLCh
     -
     • let the lightness of |current_OkLCh| be |l_origin|
     -
     • let the hue of |current_OkLCh| be |h_origin| - ³
     -
     • let |origin_rgb| be |current_OkLCh| - converted to the linear-light form of |destination| +
     • if (i > 0) +
       +
       • let |current_OkLCh| be |origin_rgb| converted to OkLCh
       +
       • let the lightness of |current_OkLCh| be |l_origin|
       +
       • let the hue of |current_OkLCh| be |h_origin| + ³
       +
       • let |origin_rgb| be |current_OkLCh| + converted to the linear-light form of |destination| +
       +
       +
     +
     • Cast a ray from |anchor| to |origin_rgb| + and let |intersection| be + the intersection of this ray + with the gamut boundary
     +
     • if an intersection was not found, + let |origin_rgb| be |last| and exit the loop + ⁵ +
     +
     • if (i >0) AND (each component of |origin_rgb| is between |low| and |high|) then + let |anchor| be |origin_rgb| + ⁴ +
     +
     • let |origin_rgb| be |intersection|
     +
     • let |last| be |intersection|
   -
   • Cast a ray from |anchor| to |origin_rgb| - and let |intersection| be - the intersection of this ray - with the gamut boundary -
   -
   • if an intersection was not found, - let |origin_rgb| be |last| and exit the loop - ⁵ -
   -
   • if (i >0) AND (each component of |origin_rgb| is between |low| and |high|) then - let |anchor| be |origin_rgb| - ⁴ -
   -
   • let |origin_rgb| be |intersection|
   -
   • let |last| be |intersection|
- -
10. let |clipped| be |origin_rgb| clipped to gamut (components in range 0 to 1), - thus trimming off any noise due to floating point inaccuracy -
-
11. return |clipped|, converted to |destination| as the gamut mapped color
- + +
12. let clip(|color|) be a function which converts |color| to |destination|, + clamps each component to the bounds of the reference range for that component + and returns the result
+
13. set |clipped| to clip(|current|)
+
14. return |clipped| as the gamut mapped color