# New Ticket Created by Nick Glencross
# Please include the string: [perl #37487]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/rt3/Ticket/Display.html?id=37487 >
I've converted circle.pasm from a really old posting
(http://www.nntp.perl.org/group/perl.perl6.internals/9814) to PIR as I
think that it would make an interesting addition to examples/pir.
I'm thinking of maybe creating a corresponding SDL version too.
Cheers,
Nick
# Copyright (C) 2005 The Perl Foundation. All rights reserved.
# $Id$
=head1 NAME
examples/pir/circle.pir - Draw a circle on any VT100-compatible screen
=head1 SYNOPSIS
% ./parrot examples/pir/circle.pir
=head1 DESCRIPTION
This draws an ASCII-art representation of a circle (or oval) using only
integer arithmetic and no trig.
The algorithm is based on:
cos(theta+delta) =
cos(theta) -
[alpha*cos(theta) + beta*sin(theta)]
and
sin(theta+delta) =
sin(theta) -
[alpha*sin(theta) - beta*cos(theta)]
where
alpha = 2*sin^2(delta/2) and beta = sin(delta)
(See Numerical Recipes in C / The Art of Scientific Computing)
In this program the value of delta is chosen to be 1/(1<<n) such
that it is small enough that
=over 4
=item * alpha is approximately 0
=item * beta is approximately delta
=back
=head1 AUTHOR
Written for parrot by Nick Glencross <[EMAIL PROTECTED]>. Adapted
from a machine code program that I wrote for a BBC micro.
=head1 COPYRIGHT
Same as parrot.
=cut
.sub circle :main
# These are configurable depending on your screen size
.local int width, height
width = 80
height = 24
# Calculate screen scaling and offset constants
.local int offset_x, offset_y, scale_x, scale_y
offset_x = width / 2
offset_y = height / 2
scale_x = 140000 / width
scale_y = 140000 / height
# Clear the screen
print "\033[H\033[2J"
# Initialise values
.local int x, y, counter
x = 0
y = 65536
counter = 0
LOOP:
# Calculate screen coordinates
.local int screen_x, screen_y
screen_x = x / scale_x
screen_x += offset_x
screen_y = y / scale_y
screen_y += offset_y
print "\033["
print screen_y
print ";"
print screen_x
print "H*"
# The magic to compute the next position
.local int temp1, temp2
temp1 = x >> 6
temp2 = y >> 6
x += temp2
y -= temp1
# Loop again
inc counter
if counter < 404 goto LOOP
# Place cursor back at bottom of screen
print "\033["
print height
print ";0H"
# Done!
end
.end
# vim: ft=imc sw=4:
