Raycaster: finding distance.

rayc.c

inline void ray(int i, float x, float y, float angle, float fisheye)
{ float fx = x - (int)x, fy = y - (int)y;
  float xstep, ystep, xdist, ydist, xx, yy, xdistadd, ydistadd;
  int xy, yx;
  int xdir = (cos(angle)<0 ? 1 : 0), ydir = (sin(angle)<0 ? 1 : 0);

  xstep = 1./tan(angle);
  xx = x + (ydir ? fy*-xstep : (1-fy)*xstep);
  xy = ydir ? (int)y : (int)y+1;
  xdist = sqrt((xx-x)*(xx-x) + (xy-y)*(xy-y));
  xdistadd = sqrt(xstep*xstep + 1);

  ystep = tan(angle);
  yx = xdir ? (int)x : (int)x+1;
  yy = y + (xdir ? fx*-ystep : (1-fx)*ystep);
  ydist = sqrt((yx-x)*(yx-x) + (yy-y)*(yy-y));
  ydistadd = sqrt(ystep*ystep + 1);

  while (1)
  { if (ydist > xdist)
    { if (xy<0 || xy>=mapy || (int)xx<0 || (int)xx>=mapx) break;
      if (map[xy-ydir][(int)xx] != '`')
      { hstretch(i, map[xy-ydir][(int)xx], ydir?1-(xx-(int)xx):xx-(int)xx, fisheye*xdist, xdist);
        break;
      }
      if (ydir) { xx -= xstep; xy--; xdist += xdistadd; }
      else  { xx += xstep; xy++; xdist += xdistadd; }
    }
    else
    { if (yx<0 || yx>=mapx || (int)yy<0 || (int)yy>=mapy) break;
      if (map[(int)yy][yx-xdir] != '`')
      { hstretch(i, map[(int)yy][yx-xdir], xdir?yy-(int)yy:1-(yy-(int)yy), fisheye*ydist, ydist);
        break;
      }
      if (xdir) { yy -= ystep; yx--; ydist += ydistadd; }
      else { yy += ystep; yx++; ydist += ydistadd; }
} } }