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Re: image scaling

From: David Kastrup
Subject: Re: image scaling
Date: Fri, 22 Feb 2008 22:52:13 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux)

Chong Yidong <address@hidden> writes:

> David Kastrup <address@hidden> writes:
>>> but it's simple enough to understand and work on; and I don't know of
>>> any performance problem in the way Emacs handles image pixmaps.
>> You must be kidding.  We have an image cache exactly because Emacs can't
>> handle images close to reasonably efficiently.
> Don't other programs use caches for images?

XEmacs, for example, does not have the equivalent, and works fine
(actually quite faster than Emacs) when using preview-latex.

The point is that when the image data is loaded into memory, Emacs still
can't display it fast.  It converts it with a painfully slow conversion
chain called for every pixel into a pixmap and caches that.  Considering
that the binary data is pretty much identical a pixmap to start with
(maybe modulo a gamma correction lookup table), this is somewhat
ridiculous.  The code paths are so muddled, however, that it is not easy
to rip this out.

Have you actually looked at the code?

David Kastrup, Kriemhildstr. 15, 44793 Bochum

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