4.3BSD - /usr/src/usr.lib/libplot/hp2648/arc.c

   1: /*
   2:  * Copyright (c) 1980 Regents of the University of California.
   3:  * All rights reserved.  The Berkeley software License Agreement
   4:  * specifies the terms and conditions for redistribution.
   5:  */
   6: 
   7: #ifndef lint
   8: static char sccsid[] = "@(#)arc.c	5.1 (Berkeley) 5/7/85";
   9: #endif not lint
  10: 
  11: #include "hp2648.h"
  12: 
  13: arc(xcent,ycent,xbeg,ybeg,xend,yend)
  14: int xcent,ycent,xbeg,ybeg,xend,yend;
  15: {
  16:     double costheta,sintheta,x,y,xn,r;
  17:     double x1,y1,x2,y2;
  18:     int xi,yi,crosspflag,crossp;
  19: 
  20:     r = (xcent-xbeg)*(xcent-xbeg)+(ycent-ybeg)*(ycent-ybeg);
  21:     r = pow(r,0.5);
  22:     if(r<1){
  23:         point(xcent,ycent);
  24:         return;
  25:     }
  26:     sintheta = 1.0/r;
  27:     costheta = pow(1-sintheta*sintheta,0.5);
  28:     xi = x = xbeg-xcent;
  29:     yi = y = ybeg-ycent;
  30:     x1 = xcent;
  31:     y1 = ycent;
  32:     x2 = xend;
  33:     y2 = yend;
  34:     crosspflag = 0;
  35:     do {
  36:         crossp = cross_product(x1,y1,x2,y2,x,y);
  37:         if(crossp >0 && crosspflag == 0) crosspflag = 1;
  38:         point(xcent+xi,ycent+yi);
  39:         xn = x;
  40:         xi = x = x*costheta + y*sintheta;
  41:         yi = y = y*costheta - xn*sintheta;
  42:     } while( crosspflag == 0 || crossp >0);
  43: }
  44: 
  45: cross_product(x1,y1,x2,y2,x3,y3)
  46: double x1,x2,x3,y1,y2,y3;
  47: {
  48:     double z,a,b;
  49:     a = (y3-y2)*(x2-x1);
  50:     b = (x3-x2)*(y2-y1);
  51:     z = a-b;
  52:     if(z<0) return(-1);
  53:     if(z>0) return(1);
  54:     return(0);
  55: }

Defined functions

Defined variables