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############################################################################
#
# File: modlines.icn
#
# Subject: Procedure to produce trace of modular lines
#
# Author: Ralph E. Griswold
#
# Date: August 3, 2000
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# For a description of the method used here, see
#
# Geometric and Artistic Graphics; Design Generation with
# Microcomputers, Jean-Paul Delahaye, Macmillan, 1987, pp. 90-95.
#
############################################################################
#
# Links: calls, gobject, gtrace
#
############################################################################
link calls
link gobject
link gtrace
# modlines produces a trace of lines between points selected modulo n,
# where n is the number of points on a supporting curve. k is an
# offset factor. A trace of the supporting curve is produced by call.
#
procedure modlines(call, m, k, limit)
local points, n, i
/limit := 500 # maximum number of points allowed
points := point_list(call, limit)
n := *points # number of points on supporting curve
every i := 0 to m do {
# i1 := i % n + 1
# i2 := (i * k) % n + 1
suspend points[(i % n + 1) | ((i * k) % n + 1)]
}
end
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