[Haskell-cafe] Re: Finding the contents of haskell platform?

[John Pybus]

Stephen Tetley wrote:
> 
> 
> I thought I read that Firefox does a font swap if it can't find a
> glyph, but thinking about it myself I can't see that this would make
> sense - Firefox would have to know an awful lot about the OSes fonts
> to know if they have "missing" glyphs.

You're pretty much right, Firefox does read the font metrics information 
of _all_ fonts on the system at startup [1].  It chooses substitute 
glyphs based on which fonts have the required glyph and matching metrics.

This font substitution can cause odd looking results if you  use odd 
characters in a run of ascii text[2], but seems to do a reasonable job 
with displaying mathematical symbols.

John


[1] Yes, this can cause significant slowdown for users with many fonts: 
<https://bugzilla.mozilla.org/show_bug.cgi?id=600713>.  I think Chrome 
just relies on a set fallback font with known wide unicode coverage.

[2] See what can happen if you cut and paste fancy content into the web 
browser, but only have ligatures defined in some unusual font: 
<http://www.undermyhat.org/blog/wp-content/uploads/2009/09/ScreenShot562.png>