Path: utzoo!attcan!uunet!husc6!bloom-beacon!EXPO.LCS.MIT.EDU!rws
From: rws@EXPO.LCS.MIT.EDU (Bob Scheifler)
Newsgroups: comp.windows.x
Subject: Re: XPutPixel
Message-ID: <8811151416.AA22845@EXPO.LCS.MIT.EDU>
Date: 15 Nov 88 14:16:32 GMT
References: <994@godot.radonc.unc.edu>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 23


    Why not make XImage.data (unsigned long *) and be
    done with it?

Umm, if you think PutPixel is slow, imagine the server having to
accept a depth 1 image (bit per pixel) in your proposed format,
and have to compact it down to a bitmap format acceptable for
blitting onto the screen.

But, I lie.  Note that in an XImage, depth and bits_per_pixel
are two separate things.  In theory, you can create an image
that is 8 bits deep but stored 32 bits_per_pixel, and then
when you get around to sending it XPutImage will do the appropriate
conversion if the bits_per_pixel doesn't match the server.
Unfortunately, Xlib doesn't have code to implement this conversion
yet, but it's *supposed* to (small consolation, I know).
Moreover, note that things like XPutPixel are actually performed
by calling functions stored in the XImage.  It is perfectly
reasonable for these functions to be specialized to the particular
image format; indeed the Xlib manual points this out.  Unfortunately,
there are some crocks in the interface routines that make this
difficult (an internal Xlib routine probably needs to be exported),
but certainly that was the intention.