# 2.11BSD#431 - /usr/src/usr.lib/libplot/hp7221/arc.c

##### Functions

    arc               X

##### Macros

    side              X

       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 "hp7221.h"
      12:
      13: /*
      14:  * 7221 requires knowing the anlge of arc.  To do this, the triangle formula
      15:  *	c^2 = a^2 + b^2 - 2*a*b*cos(angle)
      16:  * is used where "a" and "b" are the radius of the circle and "c" is the
      17:  * distance between the beginning point and the end point.
      18:  *
      19:  * This gives us "angle" or angle - 180.  To find out which, draw a line from
      20:  * beg to center.  This splits the plane in half.  All points on one side of the
      21:  * plane will have the same sign when plugged into the equation for the line.
      22:  * Pick a point on the "right side" of the line (see program below).  If "end"
      23:  * has the same sign as this point does, then they are both on the same side
      24:  * of the line and so angle is < 180.  Otherwise, angle > 180.
      25:  */
      26:
      27: #define side(x,y)   (a*(x)+b*(y)+c > 0.0 ? 1 : -1)
      28:
      29: arc(xcent,ycent,xbeg,ybeg,xend,yend)
      30: int xcent,ycent,xbeg,ybeg,xend,yend;
      31: {
      32:     double radius2, c2;
      33:     double a,b,c;
      34:     int angle;
      35:
      36:     /* Probably should check that this is really a circular arc.  */
      37:     radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg);
      38:     c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg);
      39:     angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 );
      40:
      41:     a = (double) (ycent - ybeg);
      42:     b = (double) (xcent - xbeg);
      43:     c = (double) (ycent*xbeg - xcent*ybeg);
      44:     if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend))
      45:         angle += 180;
      46:
      47:     move(xcent, ycent);
      48:     /* Not quite implemented...
      49: 	printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg);
      50: 	*/
      51: }

#### Defined functions

arc defined in line 29; never used

#### Defined variables

sccsid defined in line 8; never used

#### Defined macros

side defined in line 27; used 2 times

- in line 44(2)

Last modified: 1987-02-18 Generated: 2016-12-26 | Generated by src2html V0.67 page hit count: 772 |