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Re: redisplay system of emacs

From: grischka
Subject: Re: redisplay system of emacs
Date: Tue, 16 Feb 2010 20:20:06 +0100
User-agent: Thunderbird (Windows/20090812)

Redisplay_internal does lots and lots of computations to detect which part
of the buffer should be redisplayed at a given moment. All these
computations can be avoided using a system of subwindows (1 for every

Those computations are complicated because the buffer contents (or window
width, or scroll amount, or...) might have changed, not just because the
window might have been damaged in some complicated fashion.

It's not _that_complicated.  Basically it just draws the new screen to
memory, then compares it with the current screen and then updates the

And actually it works nicely and fast, just maybe slightly over-designed
in cases.  (For example changing "bazfoobar" to "baz,foobar" would output
",f" and "obar" and thus reuse the originally second "o" for the new first
one.  One might think that drawing one additional "o" could be faster than
two XDrawString, but so what).

Whether the code could be written to be easier to understand is a different
question but who has time for cleanups anyway.

--- grischka

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