Slow image display over network

[Stephen J. Turnbull]

Lars Magne Ingebrigtsen writes:
 > One thing I've wondered about for a while, but has become more
 > relevant lately (what with the web feeds in Gnus and stuff) is why
 > image display is so slow over remote connections.
 > 
 > Here's how to reproduce:
 > 
 > 1) ssh somewhere that's far away, so that there's plenty of latency
 > 2) open an Emacs over X 3) (put-image "/tmp/pretty-big-picture.jpg"
 > (point))
 > 
 > Depending on how big the picture is, and what the latency is, this
 > might take very long time.
 > 
 > 4) switch to a different buffer
 > 
 > This will be instantaneous.
 > 
 > 5) switch back to the buffer where the picture is
 > 
 > This will not be instantaneous, but it will be very fast.

You do understand that 4 and 5 are probably not interesting, because
the *X server* creates a pixmap, and that will be available to Emacs
for reuse via an int-sized resource ID?

That said, it has been alleged in the past that XEmacs instantiates
images more quickly than Emacs does.  You might try benchmarking Emacs
against XEmacs; if Emacs performs comparably to XEmacs, while there
still may very well be a bug, it's probably pretty hard to fix since
two rather different implementations are showing the same performance
issue.