🚀 go-pugleaf

Expires:
Sender:
Xpath: ukc eagle

In article <220@joevax.UUCP> sdh@joevax.UUCP writes:
>Question: is the resolution of the output supposed to 450 x 450,
>and are the pixels supposed to be non-square?
>I plotted the data on a macintosh(square pixels) using a routine to
>simulate gray level.  What it displayed looked like a grid on an angle
>with one squashed sphere.

The pixels are supposed to be square, but the image is actually
451 x 451 and not 450 x 450 as advertised.  Using 450 pixels
per row causes the image to appear slanted, as you say.

Q: Why 451 and not 450?
A: Look at the code (in tracer.c):

#define XMIN 100.0
#define XMAX 250.0
#define YMIN 30.0
#define YMAX 180.0
#define INC  0.333333333333

main () {
    static float    xco,
                    yco;

    for (xco = XMIN; xco < XMAX; xco += INC) {
        for (yco = YMIN; yco < YMAX; yco += INC) {

           /* generate a pixel */
        }
}

INC is actually LESS than 1/3, so even if you dont lose
precision on the repeated addition, 450 * INC is going to be
to be less than 150.  Change this to read

#define INC  0.333333333334

or calculate xco and yco from an integer pixel coordinate if
you really want 450 x 450 images.


The result is very nice - it took 6:37 minutes on our VAX 11/750
and a mere 38 minutes on our Sequent Balance 8000.
-- 

William Roberts         ARPA: liam@cs.qmc.ac.uk  (gw: cs.ucl.edu)
Queen Mary College      UUCP: liam@qmc-cs.UUCP
LONDON, UK              Tel:  01-980 4811 ext 3900