Why is screendump so touchy

[Hsuan Chang]

Guy Shaw (paralogics!shaw at uunet.uu.net) writes on March 7 (in v7n194):
> I know that if the screen is changed during a screendump, for example by
> mouse movement or by the clock hands changing, then the rasterfile may be
> corrupted and screenload will fail.  I have seen warnings about this in
> Sun's manuals and in articles in Sun-spots.  But what I have not seen is
> an explanation.

>From my recollection, I can see the answer lies in that screendump
generates a Sun Raster file, which happens to be using some kind of
encoding (Run-length?? A few month back there were quite a few discussions
about Sun Raster format, wnl might be able to point you to the relevant
sunspots issues).  Usually an encoding scheme is global in that all the
pixels are to be accessed during the encoding process.  Hence, the system
has to retain the image for at least as long as the pixels are encoded.

Hsuan Chang
Image Processing Lab     Computer Science Dept
Vanderbilt University,   Nashville, Tn 37235
(615) 322-0962 343-6259  hsc at vuse.vanderbilt.edu

[[ Discussion of the rasterfile format can be found in the following
volume 7 issues:  69, 82, 85, 88, 91, 98, 100, 106, 144.  --wnl ]]