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diff --git a/sys/gio/imdkern/imdpl.x b/sys/gio/imdkern/imdpl.x
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+++ b/sys/gio/imdkern/imdpl.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include <gki.h>
+include <gset.h>
+include	"imd.h"
+
+define	MAX_LTYPES	3	# max software line type patterns (excl. solid)
+define	MAX_LSEGMENTS	4	# max line segments per pattern
+define	LT_OFFSET	1	# offset to be subtracted from ltype code
+
+
+# IMD_POLYLINE -- Draw a polyline.  The polyline is defined by the array of
+# points P, consisting of successive (x,y) coordinate pairs.  The first point
+# is not plotted but rather defines the start of the polyline.  The remaining
+# points define line segments to be drawn.
+
+procedure imd_polyline (p, npts)
+
+short	p[ARB]			# points defining line
+int	npts			# number of points, i.e., (x,y) pairs
+
+pointer	pl
+int	x, y
+int	len_p, i
+include	"imd.com"
+
+begin
+	if (npts < 2)
+	    return
+
+	len_p = npts * 2
+
+	# Keep track of the number of drawing instructions since the last frame
+	# clear.
+	g_ndraw = g_ndraw + 1
+
+	# Update polyline attributes if necessary.
+	pl = IMD_PLAP(g_kt)
+
+	if (IMD_WIDTH(g_kt) != PL_WIDTH(pl)) {
+	    call idk_linewidth (g_out, nint (GKI_UNPACKREAL(PL_WIDTH(pl))))
+	    IMD_WIDTH(g_kt) = PL_WIDTH(pl)
+	}
+	if (IMD_COLOR(g_kt) != PL_COLOR(pl)) {
+	    call imd_color (PL_COLOR(pl))
+	    IMD_COLOR(g_kt) = PL_COLOR(pl)
+	}
+
+	if (PL_LTYPE(pl) == GL_CLEAR) {
+	    # Ignore clear (erase) polylines.
+	    ;
+
+	} else if (PL_LTYPE(pl) != GL_SOLID) {
+	    # Draw a dashed or dotted polyline of the indicated type.
+	    call imd_dashline (g_out, p, npts, PL_LTYPE(pl))
+
+	} else {
+	    # Draw a solid polyline (usual case, optimized).
+
+	    # Move to the first point.
+	    x = p[1]
+	    y = p[2]
+	    call idk_move (g_out, x, y)
+
+	    # Draw the polyline.
+	    for (i=3;  i <= len_p;  i=i+2) {
+		x = p[i]
+		y = p[i+1]
+		call idk_draw (g_out, x, y)
+	    }
+	}
+end
+
+
+# IMD_DASHLINE -- Draw a dashed or dotted polyline using the indicated line
+# style.
+
+procedure imd_dashline (g_out, p, npts, ltype)
+
+int	g_out			# output file
+short	p[ARB]			# the polyline points
+int	npts			# number of points, i.e., (x,y) pairs
+int	ltype			# desired line type
+
+bool	penup
+int	len_p, i
+real	vlen, vpos, seglen, dx, dy
+int	oldx, oldy, newx, newy, penx, peny
+int	imd_getseg()
+
+begin
+	len_p = npts * 2
+
+	oldx = p[1]; oldy = p[2]
+	call idk_move (g_out, oldx, oldy)
+
+	# Process each line segment in the polyline.
+	do i = 3, len_p, 2 {
+	    newx = p[i]
+	    newy = p[i+1]
+
+	    # Compute VLEN, the length of the polyline line segment to be
+	    # drawn, VPOS, the relative position along the line segment,
+	    # and DX and DY, the scale factors to be applied to VPOS to get
+	    # the x and y coordinates of a point along the line segment.
+
+	    dx = newx - oldx
+	    dy = newy - oldy
+	    vlen = sqrt (dx*dx + dy*dy)
+	    if (vlen < 1.0)			# GKI units
+		next
+
+	    dx = dx / vlen
+	    dy = dy / vlen
+	    vpos = 0.0
+
+	    # For each line segment, get segments of the line type pattern
+	    # until all of the current line segment has been drawn.  The pattern
+	    # wraps around indefinitely, following the polyline around the
+	    # vertices with concern only for the total length traversed.
+
+	    while (vlen - vpos >= 1.0) {
+		seglen = imd_getseg (int (vlen - vpos), penup, ltype)
+		if (seglen < 1.0)
+		    break
+
+		vpos = vpos + seglen
+		penx = oldx + vpos * dx
+		peny = oldy + vpos * dy
+
+		if (penup)
+		    call idk_move (g_out, penx, peny)
+		else
+		    call idk_draw (g_out, penx, peny)
+	    }
+
+	    oldx = newx
+	    oldy = newy
+	}
+end
+
+
+# IMD_GETSEG -- Get a segment of a line style pattern.  The segment extends
+# from the current position in the pattern to either the next penup/pendown
+# breakpoint in the pattern, or to the point MAXLEN units further along in
+# the pattern.  When the end of the pattern is reached wrap around and
+# duplicate the pattern indefinitely.
+
+int procedure imd_getseg (maxlen, penup, ltype)
+
+int	maxlen			# max length segment to be returned
+bool	penup			# [out] pen up or pen down type segment?
+int	ltype			# line type code
+
+int	seglen, seg, lt
+int	p_seg[MAX_LTYPES]
+int	p_nseg[MAX_LTYPES]
+int	p_segleft[MAX_LTYPES]
+bool	p_penup[MAX_LTYPES,MAX_LSEGMENTS]
+int	p_seglen[MAX_LTYPES,MAX_LSEGMENTS]
+include	"ltype.dat"
+
+begin
+	lt = max (1, min (MAX_LTYPES, ltype - LT_OFFSET))
+	seg = p_seg[lt]
+	penup = p_penup[lt,seg]
+
+	repeat {
+	    if (maxlen < p_segleft[lt]) {
+		seglen = maxlen
+		p_segleft[lt] = p_segleft[lt] - seglen
+	    } else {
+		seglen = p_segleft[lt]
+		seg = seg + 1
+		if (seg > p_nseg[lt])
+		    seg = 1
+		p_seg[lt] = seg
+		p_segleft[lt] = p_seglen[lt,seg]
+	    }
+	} until (seglen > 0)
+
+	return (seglen)
+end