[Bug 3512] Implement font-stretch property

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--- Comment #46 from John Daggett (:jtd)   2008-06-04 17:23:10 PDT ---
(In reply to comment #43)
> So, for what it's worth, the patch here has the same issue with narrower and
> wider that we have with bolder and lighter for font-weight; we really need to
> store an ordered list of narrower/wider values if we want to get this correct
> relative to the fonts available, on a per-character basis.  So if we fix one,
> we might want to fix the other at the same time.

That's actually what we do for bolder/lighter, at least on Mac/Windows.  The
real tricky part of the problem is dealing with synthetic bold because you need
to know whether a face was available for "weight + n steps of bolder" when
deciding whether to enable synthetic bold or not, as in the inner-most span
below:

Font family: Bongo (two weights 200, 400)

.base { font-family: Bongo; font-weight: 200; }
.b { font-weight: bolder; }

<p class=base>Should be light face
  <span class=b>with regular face
    <span class=b>and synthetic bolded regular face</span>
  </span>
</p>

So for font-stretch we may have to deal with the same issues if we're going to
do synthesized condensed/expanded (Stuart is in favor, I'm on the fence).

As for the numbers, we probably need to pass around relative widths also (e.g.
501 for "normal + 1 step wider") as we do for font-weight.