[Plplot-devel] Bug: non-integral -ori values turn box into parallelogram

[Alan W. I. <ir...@be...>]

I have recently run across an orientation bug for non-integral -ori values.
If I try

./x12c -dev xwin -ori 0.2

and hold a piece of paper up to the screen it is immediately obvious that
the box has turned into a parallelogram with corner angles which are
noticeably different from 90 deg.  This problem also occurs for the psc and
png devices.  If you would like an extreme case of this problem try a large
aspect ratio such as

./x12c -dev xwin -ori 0.2 -a 10

If you want the problem to completely disappear try an aspect ratio of unity.

./x12c -dev xwin -ori 0.2 -a 1

I suspect the core is doing something dumb like applying a rotation
transformation to normalized device coordinates (whose x,y ratio varies from
true device coordinates by typically a factor of 3/4, but you can make this
10 or unity by the above manipulations of the aspect ratio) rather than
actual device coordinates.  However, there is no way I will ever understand
the core rotation code so I cannot fix this myself.

Maurice, could you have a look at this to see if there is a quick fix
to this "parallelogram" bug?

BTW, the reason I ran into this was I was comparing how the postscript fonts
in the ps.c code and freetype.c (Andrew's version which he should shortly be
checking in) handled non-integral -ori values.  The results currently look
ugly because both codes rotate the fonts properly (x and y labels written at
90 deg with respect to each other) while the core code does not rotate the
plot properly (box angles not 90 deg unless the aspect ratio is unity).

Alan

email: ir...@be...
phone: 250-727-2902	FAX: 250-721-7715
snail-mail:
Dr. Alan W. Irwin
Department of Physics and Astronomy,
University of Victoria, P.O. Box 3055,
Victoria, British Columbia, Canada, V8W 3P6
__________________________

Linux-powered astrophysics
__________________________