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Extended colors should be clamped so they look the same in SDR and HDR layers. #47418

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Extended colors should be clamped so they look the same in SDR and HDR layers. #47418

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@mattwoodrow mattwoodrow commented Jul 1, 2025 •
edited by webkit-early-warning-system
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d0099fa

Extended colors should be clamped so they look the same in SDR and HDR layers.
https://bugs.webkit.org/show_bug.cgi?id=292226
<rdar://150231788>

Reviewed by NOBODY (OOPS!).

Compute the headroom for extended colors, and tonemap them back into the SDR
range during WebCore::Color->CGColor conversion so that they appear identical
regardless of layer backing store contents format.

* Source/WebCore/platform/graphics/cg/ColorCG.cpp:
(WebCore::headroomForColor):
(WebCore::createCGColor):

d0099fa

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@mattwoodrow
Extended colors should be clamped so they look the same in SDR and HD…
d0099fa 
…R layers.

https://bugs.webkit.org/show_bug.cgi?id=292226
<rdar://150231788>

Reviewed by NOBODY (OOPS!).

Compute the headroom for extended colors, and tonemap them back into the SDR
range during WebCore::Color->CGColor conversion so that they appear identical
regardless of layer backing store contents format.

* Source/WebCore/platform/graphics/cg/ColorCG.cpp:
(WebCore::headroomForColor):
(WebCore::createCGColor):
@mattwoodrow mattwoodrow self-assigned this Jul 1, 2025
@mattwoodrow mattwoodrow added the Images For bugs in image handling. label Jul 1, 2025
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webkit-early-warning-system commented Jul 1, 2025 •
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EWS run on current version of this PR (hash d0099fa)

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows
✅ 🧪 style ❌ 🛠 ios ❌ 🛠 mac ✅ 🛠 wpe ✅ 🛠 win
✅ 🧪 bindings ❌ 🛠 ios-sim ❌ 🛠 mac-AS-debug ✅ 🧪 wpe-wk2 ⏳ 🧪 win-tests
✅ 🧪 webkitperl ❌ 🧪 ios-wk2 ❌ 🧪 api-mac ✅ 🧪 api-wpe
❌ 🧪 ios-wk2-wpt ❌ 🧪 mac-wk1 ✅ 🛠 wpe-cairo
❌ 🧪 api-ios ❌ 🧪 mac-wk2 ✅ 🛠 gtk
❌ 🛠 vision ❌ 🧪 mac-AS-debug-wk2 ✅ 🧪 gtk-wk2
❌ 🛠 vision-sim ❌ 🧪 mac-wk2-stress ❌ 🧪 api-gtk
⏳ 🧪 vision-wk2 ❌ 🧪 mac-intel-wk2 ✅ 🛠 playstation
❌ 🛠 tv ❌ 🛠 mac-safer-cpp
❌ 🛠 tv-sim
❌ 🛠 watch
❌ 🛠 watch-sim

@mattwoodrow mattwoodrow requested a review from weinig July 1, 2025 02:49
@webkit-ews-buildbot webkit-ews-buildbot added the merging-blocked Applied to prevent a change from being merged label Jul 1, 2025
lilyspiniolas
lilyspiniolas reviewed Jul 1, 2025
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Source/WebCore/platform/graphics/cg/ColorCG.cpp
auto [c1, c2, c3, c4] = cgCompatibleComponents;
std::array<CGFloat, 4> cgFloatComponents { c1, c2, c3, c4 };

return adoptCF(CGColorCreate(cgColorSpace, cgFloatComponents.data()));
auto result = adoptCF(CGColorCreate(cgColorSpace, cgFloatComponents.data()));
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@lilyspiniolas lilyspiniolas Jul 1, 2025 •
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Suggested change
auto result = adoptCF(CGColorCreate(cgColorSpace, cgFloatComponents.data()));
RetainPtr result = adoptCF(CGColorCreate(cgColorSpace, cgFloatComponents.data()));

lilyspiniolas
lilyspiniolas reviewed Jul 1, 2025
View reviewed changes
Source/WebCore/platform/graphics/cg/ColorCG.cpp
auto result = adoptCF(CGColorCreate(cgColorSpace, cgFloatComponents.data()));

if (auto headroom = headroomForColor(color, cgColorSpace); headroom > 1) {
auto info = adoptCF(CGColorConversionInfoCreateForToneMapping(cgColorSpace, headroom, cgColorSpace, 1.0f, kCGToneMappingDefault, nullptr, nullptr));
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@lilyspiniolas lilyspiniolas Jul 1, 2025 •
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Suggested change
auto info = adoptCF(CGColorConversionInfoCreateForToneMapping(cgColorSpace, headroom, cgColorSpace, 1.0f, kCGToneMappingDefault, nullptr, nullptr));
RetainPtr info = adoptCF(CGColorConversionInfoCreateForToneMapping(cgColorSpace, headroom, cgColorSpace, 1.0f, kCGToneMappingDefault, nullptr, nullptr));

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weinig commented Jul 1, 2025

Hey @mattwoodrow, I would love to talk to you more about this, as I have a few concerns here.

  1. I don't think this is the right approach for the platform. I think CSS colors should be able to use as much headroom as they need (constrained by dynamic-range-limit). My main argument, other than it being the most obvious behavior for authors, is that if an author can use a single 1x1 pixel image to get a color, it should be able to do the same thing with a CSS color.

  2. If, in the end, the decision is made to constrain CSS colors, I don't think this is the right place to do it, as you need the output color space to properly perform this mapping. That means, it probably needs to be done at painting time in the GraphicsContext.

I'd be happy to expand on this, let me know.

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