Bug 105171 – Custom Arabic Fonts Rendered Incorrectly

• Status: RESOLVED
• Resolution: CONFIGURATION CHANGED
• Component: Text

[Wu Chiang]

Created attachment 179731 [details]
Arabic font rendering on chrome

Some Arabic fonts render incorrectly, the letters are disconnected, higher than where they should be, or lower than where they should be. Tashkeel (symbols above and below letters) are also extremely out of place. I've tested this on the latest nightly build, chrome, and the latest Safari build on Mac OS X 10.8, the issue is present in all of them. On Firefox, all the text is rendered correctly.

[Wu Chiang]

Created attachment 179732 [details]
Arabic font rendering on Safari

[Wu Chiang]

Created attachment 179733 [details]
Arabic font rendering on Firefox

[Wu Chiang]

I've attached screenshots that show incorrect rendering in Safari and Chrome in Mac OS X 10.8 and one that shows correct rendering in Firefox.

I've tested this on the latest version of Chrome on Windows 8, as well as the latest nightly version for Windows, and the text renders correctly as it does in Firefox.

This is the URL I've been using for the rendering tests:
http://www.quranexplorer.com/quran/

[Wu Chiang]

I've made a much more compact example at:
https://dl.dropbox.com/u/9658048/bugs/webkit/index.html

[Alexey Proskuryakov]

I can reproduce with <http://www.quranexplorer.com/quran/>, but <https://dl.dropbox.com/u/9658048/bugs/webkit/index.html> looks correct AFAICT.

[Radar WebKit Bug Importer]

<rdar://problem/12904599>

[Dean Jackson]

Can you upload a screenshot of the correct rendering for your compact example? Like Alexey, quranexplorer is definitely reproducing. The compact example seems to have the Tashkeel in the correct location, but maybe some of the glyphs are disconnected.

[Wu Chiang]

Created attachment 180109 [details]
Correct rendering of compact exampe on Firefox

[Wu Chiang]

Created attachment 180113 [details]
Incorrect rendering of compact example on latest WebKit nightly

[Wu Chiang]

You are correct,  the tashkeel IS in the correct place in the compact example, however some letters are shifted up as you can see in the images. It also seems to get worse if I add more text. The only problem is the vertical positioning of the glyphs in my compact example. On quranexplorer, it's the vertical positioning of parts of lines, the tashkeel, and the glyphs.

[Dean Jackson]

(In reply to comment #10)
> You are correct,  the tashkeel IS in the correct place in the compact example, however some letters are shifted up as you can see in the images. It also seems to get worse if I add more text. The only problem is the vertical positioning of the glyphs in my compact example. On quranexplorer, it's the vertical positioning of parts of lines, the tashkeel, and the glyphs.

Thanks!

[Wu Chiang]

Further testing shows that the problem goes away if Tashkeel ( diacritics ) is removed from the text.

[Wu Chiang]

Is the text rendering in WebKit for Mac OS X based on the Quartz engine? I've looked through the wiki and documentation and couldn't find an answer for this. All I've managed to find is that RenderText is in charge of rendering raw text. Does WebKit use its own rendering logic or does it rely on Quartz? If it doesn't rely on Quartz, then where are the glyphs for complex shapes determined? and where are their positions calculated?

[Glenn Adams]

(In reply to comment #13)
> Is the text rendering in WebKit for Mac OS X based on the Quartz engine? I've looked through the wiki and documentation and couldn't find an answer for this. All I've managed to find is that RenderText is in charge of rendering raw text. Does WebKit use its own rendering logic or does it rely on Quartz? If it doesn't rely on Quartz, then where are the glyphs for complex shapes determined? and where are their positions calculated?

for apple-mac port, see

WebCore/platform/graphics/mac/ComplexTextController*

[Wu Chiang]

Looks like WebKit is relying on CoreText for complex text, CoreText is what is at fault and not WebKit. I tried making a quick application using CoreText and I immediately saw the same issues. Chromium is using HarfBuzz and having the same issues as well, so I'm not entirely sure.

[Alexey Proskuryakov]

(In reply to comment #15)
> I tried making a quick application using CoreText and I immediately saw the same issues.

Can you please file a bug with this test application attached via <http://bugreport.apple.com>?

[Dean Jackson]

(In reply to comment #16)
> (In reply to comment #15)
> > I tried making a quick application using CoreText and I immediately saw the same issues.
> 
> Can you please file a bug with this test application attached via <http://bugreport.apple.com>?

I believe there already is a bug for this (other than ours above): <rdar://problem/13004368>

But, yes, if you could file another with your test application, that would be great.

[Cameron McCormack (:heycam)]

The reported content is rendering correctly these days.