Bug 223165

Summary:

Match other browsers by interpolating colors in floating point space rather than uint8_t space

Product:

WebKit

Reporter:

Sam Weinig <sam>

Component:

New Bugs

Assignee:

Sam Weinig <sam>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

graouts, ifernandez, simon.fraser, webkit-bug-importer

Priority:

Keywords:

InRadar

Version:

WebKit Nightly Build

Hardware:

Unspecified

OS:

Unspecified

Attachments:

Description	Flags
Patch	none

Sam Weinig

Reported 2021-03-14 13:08:04 PDT

Match other browsers by interpolating colors in floating point space rather than uint8_t space

Attachments
Patch (58.46 KB, patch) 2021-03-14 13:45 PDT, Sam Weinig	no flags	Details Formatted Diff Diff
Show Obsolete (1) View All Add attachment proposed patch, testcase, etc.

Sam Weinig

Comment 1 2021-03-14 13:45:17 PDT

Created attachment 423133 [details] Patch

Sam Weinig

Comment 2 2021-03-14 14:09:07 PDT Comment hidden (obsolete)

This does seem to fix WPT results, though I am curious if there is a way to do this and stay in uint8_t space using more clever rounding. For each color channel, we are doing: premultiplication: float: color.red = color.red * color.alpha uint8_t: color.red = static_cast<uint8_t>(fastDivideBy255(color.red * color.alpha + 254)) blending: float: from + (to - from) * progress uint8_t: static_cast<int>(lround(static_cast<double>(from) + static_cast<double>(to - from) * progress)) unpremultiplication: float: color.red = color.red / color.alpha uint8_t: color.red = static_cast<uint8_t>((fastMultiplyBy255(color.red) + color.alpha - 1) / color.alpha)

EWS

Comment 3 2021-03-14 23:20:08 PDT

Committed r274408: <https://commits.webkit.org/r274408> All reviewed patches have been landed. Closing bug and clearing flags on attachment 423133 [details].

Radar WebKit Bug Importer

Comment 4 2021-03-14 23:21:14 PDT

<rdar://problem/75419227>

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