/*# proc: dx_line_alloc - interpolates a line between two endpoints by incrementing# proc:                 x by single units and computing a resulting y.*/#include <defs.h>/***************************************************************************//* At call nalloc is how much memory is currently allocated for x_list and *//* y_list.  If nalloc == 0 routine will allocate needed memory based on:   *//*                                                                         *//*         asize = abs(x2-x1)+2                                            *//*                                                                         *//* If nalloc < asize will realloc memory for x_list and y_list to asize.   *//***************************************************************************/dx_line_alloc(x1,y1,x2,y2,x_list,y_list,num,nalloc)int x1,y1,x2,y2,**x_list,**y_list,*num,*nalloc;{   int x, y, i;   int dx, dy;   int x_end;   int x_incr;   float slope, fy, fy_incr;   int *xptr, *yptr;   int asize;   asize = abs(x2-x1)+2;   if(*nalloc == 0) {      *nalloc = asize;      malloc_int(x_list, *nalloc, "dx_line_alloc x_list");      malloc_int(y_list, *nalloc, "dx_line_alloc y_list");   }   else if(*nalloc < asize) {      *nalloc = asize;      realloc_int(x_list, *nalloc, "dx_line_alloc x_list");      realloc_int(y_list, *nalloc, "dx_line_alloc y_list");   }   i = 0;   dx = (x1 - x2);   dy = (y1 - y2);   xptr = *x_list;   yptr = *y_list;   /* if line is vertical, then store midpoint of line */   if(dx == 0){      x = x1;      y = y1;      xptr[i] = x1;      yptr[i++] = sround((y1+y2)/2.0);      *num = i;      return;   }   /* if line is horizontal, then store same y value along line */   if(dy == 0){      x = x1;      y = y1;      x_end = x2;      xptr[i] = x;      yptr[i++] = y;      if(x1 > x2){         while(x > x_end){            xptr[i] = --x;            yptr[i++] = y;         }      }      else{         while(x < x_end){            xptr[i] = ++x;            yptr[i++] = y;         }      }      *num = i;      return;   }   /* otherwise increment in x and use slope to update y */   slope = dy/(float)dx;   if(x1 < x2){      x_incr = 1;      fy_incr = slope;   }   else{      x_incr = -1;      fy_incr = -slope;   }   x = x1;   fy = (float)y1;   y = y1;   x_end = x2;   while(x <= x_end){      xptr[i] = x;      yptr[i++] = y;      x += x_incr;      fy += fy_incr;      y = sround(fy);   }   *num = i;   return;}