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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <gki.h>
include <gio.h>
# GPL_WCSTOGKI -- Transform world coordinates to GKI coordinates using the
# cached transformation parameters. There are three possible types of scaling
# on either axis, linear, log, and "elog". The latter is a piecewise log
# scaling function defined for all X, i.e., for negative as well as positive
# X (see elogr.x). If a negative number is transformed with normal log
# scaling it is treated as an indefinite, i.e., plotted as a gap in the plot.
procedure gpl_wcstogki (gp, wx, wy, mx, my)
pointer gp # graphics device descriptor
real wx, wy # world coordinates of point
real mx, my # metacode coordinates of point
real x, y
real elogr()
include "gpl.com"
begin
# Update cached transformation parameters if device changes, cache
# has been invalidated, or the current WCS has been changed.
if (gp != gp_out || GP_WCS(gp) != wcs)
call gpl_cache (gp)
# Transform the coordinates.
if (xtran == LINEAR) {
x = wx
} else if (xtran == LOG) {
if (wx <= 0) {
call gpl_flush()
return
} else
x = log10 (wx)
} else
x = elogr (wx)
if (ytran == LINEAR) {
y = wy
} else if (ytran == LOG) {
if (wy <= 0) {
call gpl_flush()
return
} else
y = log10 (wy)
} else
y = elogr (wy)
# Return real rather than int GKI coordinates to avoid digitization
# errors in a sequence of draws relative to the current pen position.
mx = max (0.0, min (real(GKI_MAXNDC),
((x - wxorigin) * xscale) + mxorigin))
my = max (0.0, min (real(GKI_MAXNDC),
((y - wyorigin) * yscale) + myorigin))
end
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