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From: roy@phri.UUCP
Newsgroups: comp.graphics
Subject: Bounding boxes and drawing dashed vectors in SunView
Message-ID: <2601@phri.UUCP>
Date: Tue, 24-Feb-87 12:15:45 EST
Article-I.D.: phri.2601
Posted: Tue Feb 24 12:15:45 1987
Date-Received: Fri, 27-Feb-87 05:22:32 EST
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 42


	I have two questions about the SunView pixrect package.

	First, is there an easy way to find the bounding box of a memory
pixrect?  By this I mean the smallest rectangle which encloses every
non-zero pixel in the pixrect.  We are trying to make movies on a Sun-3 by
doing screendumps of the frames we want and then doing screenloads of each
in turn.

	I have a little program which pr_load's all the screendump files
and then pr_rop's them to /dev/fb one at a time, which works fine up to
about 10 frames; then you run out of physical memory (on a [4-Meg] 3/50)
and start thrashing.  As long as you have enough physical memory, you can
zap frames up on the screen plenty fast, but a 1 second movie isn't much
fun.  Most of the frames don't come close to the edges of the screen, so we
could save a lot of core by just storing the area enclosed by the bounding
box, and an x,y offset from the origin of the screen.

	The only way I can see to find the bounding box is by brute force
raster scanning of the pixrect using pr_get(), but this is bound to be
slow.  Is there a faster way?

	My second question concerns drawing dashed vectors.  I want to
create a rubber-band effect (you paste down one endpoint of a vector, and
drag the mouse to the other endpoint, with a dashed vector being drawn so
you can see what it will look like when you release the mouse button).

	I tried the obvious way and drew the vectors through a 50% grey
screen using pr_stencil, but the results are horrible looking and terribly
slow as well.  What I really want is a way to say "draw this vector with 10
pixels on, 10 pixels off, where the on-off pattern goes by arc length
instead of x and y coordinates", just like PostScript's "setdash" operator.
Actually, I then want to XOR this with a pixrect, so I can erase it easily
when the mouse moves.  My first though was to dive into pr_vector source
and modify it to do what I want, but that would leave me with something I
couldn't distribute except to other people with source licenses.
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016

"you can't spell deoxyribonucleic without unix!"