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[css-color-4] Correction to ray trace to avoid throwing off our intersect calculation and match MINDE flow #10579 #13416

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Merged
svgeesus merged 3 commits into from
Feb 18, 2026
Merged

[css-color-4] Correction to ray trace to avoid throwing off our intersect calculation and match MINDE flow #10579 #13416

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31037c1
[css-color-4] Correction to ray trace to avoid throwing off our inter…
facelessuser Jan 30, 2026
db955e1
A little more buffer
facelessuser Feb 2, 2026
b9863d3
Match the flow CSS
facelessuser Feb 2, 2026
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78 changes: 41 additions & 37 deletions css-color-4/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -6052,9 +6052,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping</h4>

<ol>
<!-- check if we need gamut mapping at all -->
<li>if |origin| is in gamut for |destination|,
convert |origin| to |destination| and return it as the gamut mapped color
</li>
<li>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
<!-- we do, so convert to OkLCh -->
<li>let |origin_OkLCh| be |origin| converted from |origin color space|
to the OkLCh color space</li>
Expand All @@ -6071,45 +6069,51 @@ Sample Pseudocode for the Ray Trace Gamut Mapping</h4>
</li>
<li>let |origin_rgb| be |origin_OkLCh|
converted to the <em>linear-light</em> form of |destination|</li>
<li>let |low| be 1E-6 <a href="#raytrace-footnote-1"><sup>1</sup></a></li>
<li>let |high| be 1.0 - |low| <a href="#raytrace-footnote-2"><sup>2</sup></a></li>
<li>let |last| be |origin_rgb|</li>
<li>for (i=0; i&lt;4; i++)
<!-- check if we need gamut mapping at all -->
<li>if |origin_rgb| is not in gamut
<ul>
<li>if (i > 0)
<!-- we do, so perform chroma reduction -->
<li>let |low| be 0.0 + 1E-6 <a href="#raytrace-footnote-1"><sup>1</sup></a></li>
<li>let |high| be 1.0 - 1E-6 <a href="#raytrace-footnote-2"><sup>2</sup></a></li>
<li>let |last| be |origin_rgb|</li>
<li>for (i=0; i&lt;4; i++)
<ul>
<li>let |current_OkLCh| be |origin_rgb| converted to OkLCh</li>
<li>let the lightness of |current_OkLCh| be |l_origin|</li>
<li>let the hue of |current_OkLCh| be |h_origin|
<a href="#raytrace-footnote-3"><sup>3</sup></a></li>
<li>let |origin_rgb| be |current_OkLCh|
converted to the <em>linear-light</em> form of |destination|
<li>if (i > 0)
<ul>
<li>let |current_OkLCh| be |origin_rgb| converted to OkLCh</li>
<li>let the lightness of |current_OkLCh| be |l_origin|</li>
<li>let the hue of |current_OkLCh| be |h_origin|
<a href="#raytrace-footnote-3"><sup>3</sup></a></li>
<li>let |origin_rgb| be |current_OkLCh|
converted to the <em>linear-light</em> form of |destination|
</li>
</ul>
</li>
<li><b>Cast a ray</b> from |anchor| to |origin_rgb|
and let |intersection| be
the intersection of this ray
with the gamut boundary
</li>
<li>if an intersection was not found,
let |origin_rgb| be |last| and exit the loop
<a href="#raytrace-footnote-5"><sup>5</sup></a>
</li>
<li>if (i >0) AND (each component of |origin_rgb| is between |low| and |high|) then
let |anchor| be |origin_rgb|
<a href="#raytrace-footnote-4"><sup>4</sup></a>
</li>
<li>let |origin_rgb| be |intersection|</li>
<li>let |last| be |intersection|</li>
</ul>
</li>
<li><b>Cast a ray</b> from |anchor| to |origin_rgb|
and let |intersection| be
the intersection of this ray
with the gamut boundary
</li>
<li>if an intersection was not found,
let |origin_rgb| be |last| and exit the loop
<a href="#raytrace-footnote-5"><sup>5</sup></a>
</li>
<li>if (i >0) AND (each component of |origin_rgb| is between |low| and |high|) then
let |anchor| be |origin_rgb|
<a href="#raytrace-footnote-4"><sup>4</sup></a>
</li>
<li>let |origin_rgb| be |intersection|</li>
<li>let |last| be |intersection|</li>
</ul>
</li>
<!-- final tidying up -->
<li>let |clipped| be |origin_rgb| clipped to gamut (components in range 0 to 1),
thus trimming off any noise due to floating point inaccuracy
</li>
<li>return |clipped|, converted to |destination| as the gamut mapped color</li>
<!-- should those two be in the reverse order, convert to destination then clip? -->
<!-- we already excluded spaces with no gamut limits in the first step, so this is fine -->
<li>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</li>
<li>set |clipped| to clip(|current|)</li>
<li>return |clipped| as the gamut mapped color</li>
</ol>


Expand All @@ -6135,7 +6139,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping</h4>
<li>let |d| be |b| - |a|</li>
<li>let |direction|<i>[i]</i> be |d|</li>
<!-- Non parallel cases -->
<li>if (d != 0):
<li>if abs(|d|) < 1E-12
<ul>
<li>let |inv_d| be 1 / |d|</li>
<li>let |t1| be (|bmin|<i>[i]</i> - |a|) * |inv_d|</li>
Expand Down Expand Up @@ -6165,7 +6169,7 @@ Sample Pseudocode for the Ray Trace Gamut Mapping</h4>
</li>
</ul>
</li>
<li>if (|tnear| > 10)
<li>if |tnear| is infinite (or matches the initial very large value)
<ul>
<li>return INTERSECTION NOT FOUND</li>
</ul>
Expand Down