1 files changed, 59 insertions, 0 deletions
diff --git a/usr/src/ucbcmd/plot/libplot/hp7221/arc.c b/usr/src/ucbcmd/plot/libplot/hp7221/arc.c
new file mode 100644
index 0000000000..1ad9cb2c46
--- /dev/null
+++ b/usr/src/ucbcmd/plot/libplot/hp7221/arc.c
@@ -0,0 +1,59 @@
+/*	Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T	*/
+/*	  All Rights Reserved  	*/
+
+
+#ident	"%Z%%M%	%I%	%E% SMI"	/* SVr4.0 1.1	*/
+
+/*
+ * Copyright (c) 1980 Regents of the University of California.
+ * All rights reserved. The Berkeley software License Agreement
+ * specifies the terms and conditions for redistribution.
+ */
+
+/*
+ * Copyright (c) 1983, 1984 1985, 1986, 1987, 1988, Sun Microsystems, Inc.
+ * All Rights Reserved.
+ */
+
+
+#include "hp7221.h"
+
+/* 
+ * 7221 requires knowing the anlge of arc.  To do this, the triangle formula
+ *	c^2 = a^2 + b^2 - 2*a*b*cos(angle)
+ * is used where "a" and "b" are the radius of the circle and "c" is the
+ * distance between the beginning point and the end point.
+ *
+ * This gives us "angle" or angle - 180.  To find out which, draw a line from
+ * beg to center.  This splits the plane in half.  All points on one side of the
+ * plane will have the same sign when plugged into the equation for the line.
+ * Pick a point on the "right side" of the line (see program below).  If "end"
+ * has the same sign as this point does, then they are both on the same side
+ * of the line and so angle is < 180.  Otherwise, angle > 180.
+ */
+   
+#define side(x,y)	(a*(x)+b*(y)+c > 0.0 ? 1 : -1)
+
+arc(xcent,ycent,xbeg,ybeg,xend,yend)
+int xcent,ycent,xbeg,ybeg,xend,yend;
+{
+	double radius2, c2;
+	double a,b,c;
+	int angle;
+
+	/* Probably should check that this is really a circular arc.  */
+	radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg);
+	c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg);
+	angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 );
+
+	a = (double) (ycent - ybeg);
+	b = (double) (xcent - xbeg);
+	c = (double) (ycent*xbeg - xcent*ybeg);
+	if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend))
+		angle += 180;
+	
+	move(xcent, ycent);
+	/* Not quite implemented...
+	printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg);
+	*/
+}