Bug 145678 – [iOS] Emoji overlap preceding lines

• Component: New Bugs
• Status: RESOLVED FIXED

[Myles C. Maxfield]

[iOS] Emoji overlap preceeding lines

[Myles C. Maxfield]

Created attachment 254329 [details]
Patch

[Myles C. Maxfield]

<rdar://problem/10684914>

[Myles C. Maxfield]

Created attachment 254331 [details]
Patch

[Build Bot]

Comment on attachment 254331 [details]
Patch

Attachment 254331 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.appspot.com/results/6167040318504960

New failing tests:
fast/text/emoji.html

[Build Bot]

Created attachment 254332 [details]
Archive of layout-test-results from ews100 for mac-mavericks

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews100  Port: mac-mavericks  Platform: Mac OS X 10.9.5

[Build Bot]

Comment on attachment 254331 [details]
Patch

Attachment 254331 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.appspot.com/results/5770894412611584

New failing tests:
fast/text/emoji.html

[Build Bot]

Created attachment 254333 [details]
Archive of layout-test-results from ews104 for mac-mavericks-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews104  Port: mac-mavericks-wk2  Platform: Mac OS X 10.9.5

[Myles C. Maxfield]

Created attachment 254336 [details]
Patch

[Darin Adler]

Comment on attachment 254336 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=254336&action=review

> Source/WebCore/platform/graphics/cocoa/FontCocoa.mm:-275
> -        m_fontMetrics.setLineSpacing(0);

Maybe the real intention here was to set the line spacing to m_platformData.size()?

[Myles C. Maxfield]

Comment on attachment 254336 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=254336&action=review

>> Source/WebCore/platform/graphics/cocoa/FontCocoa.mm:-275
>> -        m_fontMetrics.setLineSpacing(0);
> 
> Maybe the real intention here was to set the line spacing to m_platformData.size()?

I tried that, but that value was too low to actually solve the problem.

[Myles C. Maxfield]

I talked with Enrica, and we came up with some interesting points.

1. The line-height of the lines inside a block is calculated to be the maximum of the line-heights of the constituent fonts. This means that, if the emoji's line height is 0, emoji won't affect the line spacing of a paragraph that it's within.

2. It is possible to trigger this bug if the natural line-height of the font used for the surrounding text is significantly smaller than the natural line height of the emoji font, but in practice, this seems rare.

2. Assuming #2 does not occur, the bug does not present itself if there are any non-emoji characters which are siblings of the emoji (because of the maximum line-height rule described in #1).

3. Assuming #2 does not occur, the bug only presents itself if the block is styled with "font-family: 'Apple Color Emoji' (, other fallback fonts)". This is a structure which Apple's Mail client should never emit.

[Myles C. Maxfield]

(In reply to comment #11)
> I talked with Enrica, and we came up with some interesting points.
> 
> 1. The line-height of the lines inside a block is calculated to be the
> maximum of the line-heights of the constituent fonts. This means that, if
> the emoji's line height is 0, emoji won't affect the line spacing of a
> paragraph that it's within.
> 
> 2. It is possible to trigger this bug if the natural line-height of the font
> used for the surrounding text is significantly smaller than the natural line
> height of the emoji font, but in practice, this seems rare.
> 
> 2. Assuming #2 does not occur, the bug does not present itself if there are
> any non-emoji characters which are siblings of the emoji (because of the
> maximum line-height rule described in #1).
> 
> 3. Assuming #2 does not occur, the bug only presents itself if the block is
> styled with "font-family: 'Apple Color Emoji' (, other fallback fonts)".
> This is a structure which Apple's Mail client should never emit.

Note that, related to the last item, the font that causes this bug is Apple-specific, yet Apple's mail client won't emit markup which triggers this. This means that the bug is rare.

[Myles C. Maxfield]

<rdar://problem/21263287>

[Enrica Casucci]

Comment on attachment 254336 [details]
Patch

I discussed this with Myles at length. Setting lineSpacing to 0 was used in earlier versions of WebKit for iOS and it is no longer needed.

[Myles C. Maxfield]

(In reply to comment #14)
> Comment on attachment 254336 [details]
> Patch
> 
> I discussed this with Myles at length. Setting lineSpacing to 0 was used in
> earlier versions of WebKit for iOS and it is no longer needed.

And Dan chimed in!

[Myles C. Maxfield]

Committed r185266: <http://trac.webkit.org/changeset/185266>