50 lines
1.7 KiB
C
50 lines
1.7 KiB
C
/*
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* Copyright (c) 1980 Regents of the University of California.
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* All rights reserved. The Berkeley software License Agreement
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* specifies the terms and conditions for redistribution.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)arc.c 1.1 94/10/31 SMI"; /* from UCB 5.1 5/7/85 */
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#endif not lint
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#include "gigi.h"
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/*
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* gigi requires knowing the anlge of arc. To do this, the triangle formula
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* c^2 = a^2 + b^2 - 2*a*b*cos(angle)
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* is used where "a" and "b" are the radius of the circle and "c" is the
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* distance between the beginning point and the end point.
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*
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* This gives us "angle" or angle - 180. To find out which, draw a line from
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* beg to center. This splits the plane in half. All points on one side of the
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* plane will have the same sign when plugged into the equation for the line.
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* Pick a point on the "right side" of the line (see program below). If "end"
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* has the same sign as this point does, then they are both on the same side
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* of the line and so angle is < 180. Otherwise, angle > 180.
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*/
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#define side(x,y) (a*(x)+b*(y)+c > 0.0 ? 1 : -1)
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arc(xcent,ycent,xbeg,ybeg,xend,yend)
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int xcent,ycent,xbeg,ybeg,xend,yend;
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{
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double radius2, c2;
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double a,b,c;
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int angle;
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/* Probably should check that this is really a circular arc. */
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radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg);
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c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg);
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angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 );
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a = (double) (ycent - ybeg);
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b = (double) (xcent - xbeg);
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c = (double) (ycent*xbeg - xcent*ybeg);
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if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend))
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angle += 180;
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move(xcent, ycent);
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printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg);
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}
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