Bug 53947 – REGRESSION (r78201): -webkit-font-smoothing:antialiased turns off ClearType

• Status: RESOLVED
• Resolution: WONTFIX
• Component: Layout and Rendering

[Adam Roben (:aroben)]

To reproduce:

1. Go to http://www.apple.com/startpage/ and look at the text
2. Set WEBKIT2_USE_NEW_DRAWING_AREA=1, relaunch, and go back to apple.com/startpage

The text is less bold with the new drawing area. See screenshots.

[Adam Roben (:aroben)]

Created attachment 81528 [details]
Part of apple.com/startpage with the old drawing area

[Adam Roben (:aroben)]

Created attachment 81529 [details]
Part of apple.com/startpage with the new drawing area

[Adam Roben (:aroben)]

<rdar://problem/8968347>

[Adam Roben (:aroben)]

The new drawing area won't be on by default until bug 53805 is fixed.

[Adam Roben (:aroben)]

It looks like we're not getting subpixel antialiasing when using the new drawing area.

[Adam Roben (:aroben)]

I tried changing ShareableBitmap::createGraphicsContext to pass kCGImageAlphaNoneSkipFirst to CGBitmapContextCreate, but that had no effect on this bug.

Text on apple.com/startpage should not be subpixel-antialiased, since the page specifies "-webkit-font-smoothing: antialiased;" on its body element. It is not subpixel-antialiased in Safari 5.0.3 on Mac OS X. Nice progression.

[Adam Roben (:aroben)]

Thanks for the clarification, Dan. I guess it is technically a progression in this case, but it seems likely to be a regression in other cases. Disabling that -webkit-font-smoothing rule in the Inspector doesn't restore the subpixel antialiasing.

[Adam Roben (:aroben)]

It looks like -webkit-font-smoothing:antialiased isn't respected for GDI text, even in WebKit1. I filed bug 54004 about this.

[Adam Roben (:aroben)]

The text on webkit.org is subpixel-antialiased, even with the new drawing area. I wonder what makes the text on apple.com/startpage different?

[Adam Roben (:aroben)]

I have a sneaking suspicion that the underlying issue here is that the GraphicsContext that DrawingAreaImpl draws the page into isn't backed by an HDC/HBITMAP.

[Adam Roben (:aroben)]

Now that the new drawing area is on by default (see bug 53805), it's easiest to just compare the rendering to WebKit1.

This bug should probably be retitled to describe a real issue and not a case of correct behavior.

[Adam Roben (:aroben)]

Here's a much better example: http://www.bbc.co.uk/news/science-environment-12911806

That page has subpixel antialiasing in WebKit1, but not in WebKit2.

[Adam Roben (:aroben)]

(In reply to comment #14)
> Here's a much better example: http://www.bbc.co.uk/news/science-environment-12911806
> 
> That page has subpixel antialiasing in WebKit1, but not in WebKit2.

This page specifies "-webkit-font-smoothing: antialiased", too, so is a progression from WebKit1.

I guess we don't have any evidence that there is a bug here. There is definitely a change in behavior. (GDI text is now affected by -webkit-font-smoothing, but wasn't previously.)

[Adam Roben (:aroben)]

Presumably the sites that are using -webkit-font-smoothing were testing on Mac or with CG font rendering on Windows, since it had no effect with GDI font rendering in Safari 5. It's hard to say whether the new behavior is better than the old behavior from a compatibility standpoint, though it's obviously more correct.