ftp.nice.ch/pub/next/unix/developer/plplot.3.0.s.tar.gz#/plplot/src/genlin.c

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/* General line-drawing routine which takes line styles into account */

#include "plplot.h"
#include <math.h>

static int lastx = -100000, lasty = -100000;

void genlin(x1,y1,x2,y2)
int x1,y1,x2,y2;
{
   int nx,ny;
   int *nms, *mark, *space;
   int *curel, *pendn, *timecnt, *alarm;
   int modulo, incr, dx, dy, diax, diay, i, temp, x, y;
   int px, py, tstep;
   int umx, umy;

/* Check for solid line */

   gmark(&mark,&space,&nms);

   if (*nms == 0) {
      grline(x1,y1,x2,y2);
      return;
   }

/* Check if pattern needs to be restarted */

   gcure(&curel,&pendn,&timecnt,&alarm);
   if (x1 != lastx || y1 != lasty) {
        *curel = 0;
        *pendn = 1;
        *timecnt = 0;
        *alarm = mark[0];
   }

   lastx = x1;
   lasty = y1;

   if (x1 == x2 && y1 == y2) return;

   nx = x2 - x1;
   ny = y2 - y1;

   if (ABS(ny) > ABS(nx)) {
        modulo = ABS(ny);
        incr   = ABS(nx);
        dx     = 0;
        dy     = (ny > 0) ? 1 : -1;
   }
   else {
        modulo = ABS(nx);
        incr   = ABS(ny);
        dx     = (nx > 0) ? 1 : -1;
        dy     = 0;
   }

   diax = (nx > 0) ? 1 : -1;
   diay = (ny > 0) ? 1 : -1;

   temp = modulo/2;
   x = x1;
   y = y1;

/* Compute the timer step */

   gumpix(&umx, &umy);
   tstep = sqrt(pow((double)(ABS(nx)*umx),2.)+
                   pow((double)(ABS(ny)*umy),2.))/modulo;

   for(i=0; i<modulo; i++) {
     temp = temp+incr;
     px = x;
     py = y;
     if (temp > modulo) {
          temp = temp-modulo;
          x = x + diax;
          y = y + diay;
     }
     else {
          x = x + dx;
          y = y + dy;
     }
     *timecnt += tstep;
     if (*timecnt >= *alarm) {
          plupd(*nms,mark,space,curel,pendn,timecnt,alarm);
          if (*pendn == 0) grline(lastx,lasty,px,py);
          lastx = x;
          lasty = y;
     }
   }

   if (*pendn != 0) grline(lastx,lasty,x,y);
   lastx = x2;
   lasty = y2;
}

These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Marcel Waldvogel and Netfuture.ch.