Bug 305636

Summary:

Google Fonts page loads extremely slowly in WebKit

Product:

WebKit

Reporter:

Daniel Jalkut <jalkut>

Component:

Text

Assignee:

Nobody <webkit-unassigned>

Status:

NEW

Severity:

Normal

CC:

ap, fantasai.bugs, graouts, karlcow, rik, sabouhallawa, simon.fraser, vitor.roriz, webkit-bug-importer, zalan

Priority:

Keywords:

InRadar

Version:

Safari 26

Hardware:

Mac (Apple Silicon)

OS:

macOS 26

Attachments:

Description	Flags
Instruments trace of Safari's WebKit process loading the page	none
Instruments trace of Brave's Chrome process loading the page	none

Daniel Jalkut

Reported 2026-01-16 05:20:16 PST

Created attachment 478042 [details] Instruments trace of Safari's WebKit process loading the page Loading the URL: https://fonts.google.com/noto/specimen/Noto+Color+Emoji in Safari takes about 30 seconds on my M4 Max MacBook Pro. Analysis under Instruments suggests the page's WebKit rendering process spends an inordinate amount of time in OTSVG, presumably handling OpenType-SVG fonts. I'm attaching two Instruments traces. One of the Safari/WebKit web process, and one of the Brave/Chrome web process, each loading the same page. The Chrome renderer finishes in a fraction of a second.

Attachments
Instruments trace of Safari's WebKit process loading the page (6.70 MB, application/zip) 2026-01-16 05:20 PST, Daniel Jalkut	no flags	Details
Instruments trace of Brave's Chrome process loading the page (4.12 MB, application/zip) 2026-01-16 05:20 PST, Daniel Jalkut	no flags	Details
View All Add attachment proposed patch, testcase, etc.

Daniel Jalkut

Comment 1 2026-01-16 05:20:51 PST

Created attachment 478043 [details] Instruments trace of Brave's Chrome process loading the page

Radar WebKit Bug Importer

Comment 2 2026-01-16 06:56:46 PST

<rdar://problem/168301160>

Alexey Proskuryakov

Comment 3 2026-01-16 18:58:23 PST

It's spending all the time in CTFontGetBoundingRectsFromGlyphs, executed via Element.offsetWidth() and Element.offsetLeft(). Creating a whole new SVG document each time. When I tested this on my Mac, I saw an even worse issue after switching from this tab and back, it was hung in the same way, but in normal layout, not any JavaScript program.

Simon Fraser (smfr)

Comment 4 2026-01-16 19:12:17 PST

It's spending time CoreSVG, not WebKit's SVG code.

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