[webkit-dev] font metrics

David Hyatt hyatt at apple.com
Thu Jan 11 15:58:55 PST 2007

This is an architectural flaw right now.  I broke the ability to  
flush the cache when porting the code from Obj-C to C++, because I  
lost the reference counting aspect of the font cache.

You basically want the ability to flush the cache.

My suggested approach would be to re-architect things so that  
FontData and FontPlatformData are actually reference-counted objects.

Right now font lookup is a 2-step process primarily just for Mac.

You go from:

FontDescription -> FontPlatformData

and then from

FontPlatformData -> FontData

On the Mac, FontPlatformData doesn't need to be reference-counted,  
since it wraps an NSFont, which is already reference-counted and  
canonical (so that the same font will yield the same NSFont*).   
Because it's canonicalized, you can actually easily go from NSFont ->  

In order to flush the cache easily, you need FontData to be reference- 
counted so that the cache can drop references, and then the  
individual RenderStyles can drop references as they go away.

FontPlatformData is the sticky bit though.  FontPlatformData will  
have to properly reference-count its internal object on all  
platforms.  The easiest way to guarantee this works on all platforms  
would probably be to just make FontPlatformData reference-counted  
too.  If this is done, the retains and releases of the NSFont on Mac  
could be dropped from FontPlatformData's constructors and destructors  
on Mac.

I don't really have plans to get to this soon, so this would  
definitely be an area in which you could help out. :)

(hyatt at apple.com)

On Jan 11, 2007, at 1:26 PM, Mike Reed wrote:

> In the (nearly) latest version, webkit is caching glyph metrics based
> on font+pointSize. If my device characteristics change (e.g. screen
> res), I think I need to invalidate those widths (or spawn a new set),
> so that measuring and drawing reflect the new values.
> Any pointers to help me with my port?
> _______________________________________________
> webkit-dev mailing list
> webkit-dev at lists.webkit.org
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