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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <gki.h>
include <fset.h>
include "../lib/ids.h"
define MAXC 10000 # just a largish int here
# IDS_VECTOR -- Plot a line in the current plane; the starting coordinates
# are in ids.com: i_pt_x, i_pt_y. The end points are the arguments
# to vector.
# the code is Bresenham's algorithm, as taken from the line drawing
# routine in Forth-11 image display code.
procedure ids_vector (ax,ay)
short ax,ay # vector end coordinates, GKI
short x,y
short xe ,ye # end coordinates, device
short dx,dy,dd
short xi,yi, xid,yid # increments
short total, e # total change and error
int bufsize # file i/o buffersize
int fstati()
int count, cmax
include "../lib/ids.com"
begin
x = ax
y = ay
bufsize = fstati(i_out, F_BUFSIZE)
# convert x,y to device coords.
xe = real(x) * i_xres /(GKI_MAXNDC+1)
ye = real(y) * i_yres /(GKI_MAXNDC+1)
# determine delta x and y, and x/y increments
dx = xe - i_pt_x
dy = ye - i_pt_y
# set movement increments, take absolute value of dx, dy
if ( dy >= 0 )
yi = 1
else {
yi = -1
dy = -dy
}
if ( dx >= 0 )
xi = 1
else {
xi = -1
dx = -dx
}
# set diagonal movement increments
xid = xi
yid = yi
# if, for instance, pos. slope less than 45 degrees, most movement
# is in x, so then set (the ususal) y increment to zero
if ( dy >= dx )
xi = 0
else
yi = 0
# Set up for buffer of one, and let code find best buffering
cmax = 0
call fseti(i_out, F_BUFSIZE, 1)
count = 0
# Plot the first point
call ids_rpoint (0, 0)
# Is there anything to do? determine total increments to plot; if
# zero, quit
total = dx + dy
if ( total == 0 ) {
call fseti (i_out, F_BUFSIZE, bufsize)
return
}
# set error to zero, determine difference in x,y change.
e = 0
dd = dy - dx
if ( dd >= 0 ) {
dd = -dd
dy = dx
}
# plot the line
repeat {
dx = dd + e
if ( (dy + e + dx) >= 0 ) {
# diagonal plot, accounts for two units of increment
if ( count > cmax ) {
# leaving current (x) line, so determine how many points
# have plotted on line and use this (maximum) as line
# buffering size
call fseti(i_out, F_BUFSIZE, count)
cmax = count
count = 0
}
call ids_rpoint ( xid, yid )
total = total - 2
e = dx
} else {
# move in x (or y) only; for the small positive slope line,
# real line will move up and finally over line being plotted,
# hence e increases.
call ids_rpoint ( xi, yi )
total = total - 1
e = e + dy
count = count + 1
}
} until ( total <= 0 )
# restore original buffer size
call fseti(i_out, F_BUFSIZE, bufsize)
end
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