Behdad Esfahbod's daily notes on GNOME, Pango, Fedora, Persian Computing, Bob Dylan, and Dan Bern!

My Photo
Name:
Location: Toronto, Ontario, Canada

Ask Google.

Contact info
Google
Hacker Emblem Become a Friend of GNOME I Power Blogger
follow me on Twitter
Archives
July 2003
August 2003
October 2003
November 2003
December 2003
March 2004
April 2004
May 2004
July 2004
August 2004
September 2004
November 2004
March 2005
April 2005
May 2005
June 2005
July 2005
August 2005
September 2005
October 2005
November 2005
December 2005
January 2006
February 2006
March 2006
April 2006
May 2006
June 2006
July 2006
August 2006
September 2006
October 2006
November 2006
December 2006
January 2007
February 2007
March 2007
April 2007
May 2007
June 2007
July 2007
August 2007
September 2007
October 2007
November 2007
December 2007
January 2008
February 2008
March 2008
April 2008
May 2008
June 2008
July 2008
August 2008
October 2008
November 2008
December 2008
January 2009
March 2009
April 2009
May 2009
June 2009
July 2009
August 2009
November 2009
December 2009
March 2010
April 2010
May 2010
June 2010
July 2010
October 2010
November 2010
April 2011
May 2011
August 2011
September 2011
October 2011
November 2011
November 2012
June 2013
January 2014
Current Posts
McEs, A Hacker Life
Wednesday, November 18, 2009
 Pango vs HarfBuzz

Since the rewritten HarfBuzz is shaping up fast and getting lots of Buzz these days, I get asked the same question again and again: "Will HarfBuzz replace Pango?" This post tries to answer that.


Short answer: No, not at all! Pango is here to stay. It will change, but only get better.


Long answer:

Pango provides two levels of API: A low-level and a high-level.

Low level API: What I can the "three pillars of pango":

High-level API: Pango's high-level API consists of the PangoLayout object, aka "here's a piece of text render it in this box I don't care what you do."

Of these, HarfBuzz only does shaping. That is, hb_shape() is functionally equivalent to pango_shape().


API implications: Here is how moving to HarfBuzz affects the Pango API:

Pango Modules: pango_shape() calls into Pango shaper modules to get the actual shaping done. There are two kinds Pango shaper modules depending on what they do (the API is the same, so Pango doesn't differentiate between the two classes):
Now, as HarfBuzz becomes the shaping engine on Linux, all those script-specific modules will be removed and basic-fc will simply call into hb_shape(). That's indeed what the basic-fc.c in the harfbuzz-ng-external does.

Later on, when we add support for native win32, CoreText, Graphite, and m17n to HarfBuzz, all those other modules will also be replaced by HarfBuzz-calling equivalents.

Which one to use: Pango or HarfBuzz? Depends.

PangoLayout is designed to be the 'render this text in this box I don't care how' kind of API. That's a perfect fit for GUI toolkits like GTK+, but not suitable for lots of other uses, for example:
while in many of those cases PangoLayout can be made to work (with much pain, mind you), Pango still provides the lower level API and lots of other bits and pieces to get something going. What it doesn't give full control on however is font selection, which happens to be a deal-breaker for many of those usecases (browsers following CSS rules, etc).

So, each of those kinds of applications need to assess the pros and cons of using Pango vs using HarBuzz and providing all the other bits themselves. For example, HarfBuzz doesn't provide:
There's also a hybrid use possible: to borrow those pieces from Pango on platforms that it's feasable, but drive HarfBuzz directly. It all depends. When in doubt, ask! We have a mailing list.

That said, Firefox will use HarfBuzz as soon as it's ready (there are patches circulating around). Google is using old HarfBuzz for their Webkit and will port to the new one. I'm also attending the Webkit-GTK hackfest in December to port that to the new HarfBuzz. We'll work towards sharing the HarfBuzz-dealing code among Webkit backends.

This is already a long post. Let me finish now. Hope I made it a tiny bit more clear.

Labels: , , ,

Comments:
Should the second pango_itemize() have been a pango_shape()?
 
Thanks James. Indeed. Fixed.
 
After reading "It will change, but only get better." I stopped, went happily to sleep, dreamed of this arrsome hacker and did not feel any need to continue reading his blog post. ;-)
 
Any news about Qt? They're currently using the old HarfBuzz, do you know whether and when they plan to pick up HarfBuzz-ng?
 
Kevin: No concrete news, but I'm in close contact with them. I expect switching it over to the new code will be an afternoon worth of hacking for them.

Andre: I love you too! I'll be in Germany for holidays, lets hook up :D
 
What about Microsoft's MATH enabled opentype fonts? Can harfbuzz help with mathml implementation?
 
Regarding the MATH table, it's not in our immediate plan to implement that. And it's a totally separate feature. But we can expose the table using our infrastructure. It's up to applications to build a renderer on top of that though.
 
Post a Comment

Links to this post:

Create a Link



<< Archive
<< Home