Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!snorkelwacker!bloom-beacon!SABER.COM!jimf
From: jimf@SABER.COM
Newsgroups: comp.windows.x
Subject: Re: Pixmap vs. Image
Message-ID: <9006031425.AA05232@bowie>
Date: 3 Jun 90 14:25:05 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 32

|My understanding, so far, is that images (Ximage structure) reside
|on the client and shipping them to my window can take lots of time
|(many <<dozens of?>> seconds) for large images.  Pixmaps, however,
|reside on the workstation (server) and can be loaded into the
|window much faster.  Here's the question:
|
|If I have to do these computations (an add and multiply) on each pixel,
|and load the result into a window.  First, where do the computations
|take place (server or client)?  Second, if they take place on the
|client, is it faster to use Images which are already there, or use
|Pixmaps which seems to imply a round trip for each pixel?  Which is
|faster, which is easier, which is politically correct????

If you're doing heavy image manipulation, do it in the client and ship
a finished XImage to the server.  This is much faster than doing
per-pixel manipulations (which are still done on the client but which
will be sent one-at-a time to the server).

I suggest, however, sending the image to a pixmap and using the pixmap
to blit to the window.  This means you only send the processed image
once, although it can potentially use a lot of memory in the server.

I don't know why it's taking so long to send an XImage to your server;
in practice I can send large 8-bit images over the network in a couple
of seconds, and even faster locally.

I suggest looking at the code to xloadimage, which does a variety of
simple image processing functions.

jim frost
saber software
jimf@saber.com