Bug 290996 – [GTK] Emoji displayed in text mode in Webkit, but with colour in Firefox/Chromium

• Component: WebKitGTK
• Status: NEW

[Дилян Палаузов]

Created attachment 474816 [details]
Sample with emoji with(out) colour

Loading https://cal.aegee.org/s/0/e947872a-224b-4c84-8d25-90a541a9ec6-318.ics_en.html (the attached file) with webkitgtk-6.0/MiniBrowser 2.48.0, webkit2gtk-4.1/MiniBrowser 2.48.0 and Epiphany 46.3 shows the island on the first line in text mode, but loading the same file with Chromium or Firefox on Linux shows the island in colour.

Cf: https://gitlab.gnome.org/GNOME/evolution/-/issues/3031

Emoji code f0 9f 8f 9d  Desert Island.

Actual text under hexdump

000028d0  61 0d 0a 53 55 4d 4d 41  52 59 3a 4e 57 4d 3a 20  |a..SUMMARY:NWM: |
000028e0  50 65 73 63 61 72 61 5c  2c 20 74 68 65 20 6e 65  |Pescara\, the ne|
000028f0  78 74 20 74 72 65 61 73  75 72 65 20 69 73 6c 61  |xt treasure isla|
00002900  6e 64 f0 9f 8f 9d ef b8  8f 20 21 0d 0a 55 49 44  |nd....... !..UID|

[Radar WebKit Bug Importer]

<rdar://problem/148517738>

[Дилян Палаузов]

When I click on an event at https://cal.aegee.org there is an Unicode clock followed by Unicode variation selector 15.  So this clock should be in text-form (without colours).

In MiniBrowser the clock in shown with colour, so the selector 15 is ignored, but in Firefox and Chromium on Linux there is no colour in the clock.

That said, WebKit(GTK?) does not have correct understanding when Unicode variation selector 15 should be applied.  Sometimes it is applied, when the selector it is missing, and sometimes selector 15 is present, but is not applied.

[Дилян Палаузов]

N.B. after the island above is included expicit Unicode Variation Selector 16, which is supposed to enforce the colour form of the emoji.

[Michael Catanzaro]

I see the old FontCascade::fontForCombiningCharacterSequence in FontCairoHarfbuzzNG.cpp has code to support color emoji, but the new FontCascade::fontForCombiningCharacterSequence in FontCascadeSkia.cpp notably does not.

[Michael Catanzaro]

Possibly also related to bug #259205