Re: Emacs defeats ClearType

[David Abrahams <dave@boost-consulting.com>]

jasonr@f2s.com writes:

> Quoting David Abrahams <dave@boost-consulting.com>:
>
>> Incidentally, it seemed to work just fine for me if I remove the
>> checks for whether cleartype is enabled altogether, and just make the
>> width adjustments unconditionally.
>
> That is not a good idea. Your patch potentially affects performance,
> since it tells lies about the width of characters to counteract the
> system's lies, and may make them appear to be wider than their
> bounding box when they are not. If a character being redisplayed is
> detected to be wider than its bounding box, then the next character
> needs to be redrawn also, possibly cascading out to the full line in
> the worst cases. So we should only tell these lies when we know the
> system could be lying.

Yes, if you're concerned about redrawing the minimum possible number
of characters on a line, you don't want to do that.  I think that's a
needless optimization in most cases, but I'm sure there are machines
and buffers where you can observe a difference in speed.

> What would be better is to do the test for Cleartype once per font
> and cache the result. Actually, you use a system setting for the
> test, so if there is not a way to find out if Cleartype is used for
> a specific font (I think there is), then a single test at startup is
> all that will be needed.

But then you'll pay for your evil lies even when the user turns off
ClearType during an emacs session, and the user who turns on ClearType
during an emacs session will get poor visual results and probably
conclude that Emacs doesn't work with ClearType.

Anyway, please let me know if you want to take what I've done and
massage it yourself or if you'd like me to make specific changes so it
can be integrated into the Emacs sourcebase.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com