Mocha Doom PathTrasverse

/**
     * P_PathTraverse
     * Traces a line from x1,y1 to x2,y2,
     * calling the traverser function for each.
     * Returns true if the traverser function returns true
     * for all lines.
     */
    boolean PathTraverse ( int x1,int y1,int x2,int y2,int flags,PTR_InterceptFunc trav)
    {
   //   System.out.println("Pathtraverse "+x1+" , " +y1+" to "+x2 +" , " +y2);
     int xt1,yt1;
     int xt2, yt2;
     long _x1, _x2, _y1, _y2;
     int xstep,ystep;

     int partial;

     int xintercept, yintercept;

     int     mapx;
     int     mapy;

     int     mapxstep;
     int     mapystep;

     int     count;

     earlyout = flags(flags ,PT_EARLYOUT);

     R.increaseValidCount(1);
     intercept_p = 0;

     if ( ((x1-LL.bmaporgx)&(MAPBLOCKSIZE-1)) == 0)
     x1 += FRACUNIT; // don't side exactly on a line

     if ( ((y1-LL.bmaporgy)&(MAPBLOCKSIZE-1)) == 0)
     y1 += FRACUNIT; // don't side exactly on a line

     trace.x = x1;
     trace.y = y1;
     trace.dx = x2 - x1;
     trace.dy = y2 - y1;

     /*
     _x1 = (long)x1 - LL.bmaporgx;
     _y1 = (long)y1 - LL.bmaporgy;
     x1 -= LL.bmaporgx;
     y1 -= LL.bmaporgy;
     xt1 = LL.getSafeBlockX(_x1);
     yt1 = LL.getSafeBlockY(_y1);

     _x2 = (long)x2 - LL.bmaporgx;
     _y2 = (long)y2 - LL.bmaporgy;
     x2 -= LL.bmaporgx;
     y2 -= LL.bmaporgy;


     xt2 = LL.getSafeBlockX(_x2);
     yt2 = LL.getSafeBlockY(_y2);
     */
     {

            _x1 = (long)x1 - LL.bmaporgx;
            _y1 = (long)y1 - LL.bmaporgy;
            xt1 = (int)(_x1>>MAPBLOCKSHIFT);
            yt1 = (int)(_y1>>MAPBLOCKSHIFT);

          //  mapx1 = (int)(_x1>>MAPBTOFRAC);
          //  mapy1 = (int)(_y1>>MAPBTOFRAC);

            _x2 = (long)x2 - LL.bmaporgx;
            _y2 = (long)y2 - LL.bmaporgy;
            xt2 = (int)(_x2>>MAPBLOCKSHIFT);
            yt2 = (int)(_y2>>MAPBLOCKSHIFT);

            x1 -= LL.bmaporgx;
            y1 -= LL.bmaporgy;
            x2 -= LL.bmaporgx;
            y2 -= LL.bmaporgy;
          }

    // System.out.printf("Block: %d %d %d %d\n",xt1,yt1,xt2,yt2);

     if (xt2 > xt1)
     {
     mapxstep = 1;
     partial = FRACUNIT - ((x1>>MAPBTOFRAC)&(FRACUNIT-1));
     ystep = FixedDiv ((int)(y2-y1),Math.abs((int)(x2-x1)));
     }
     else if (xt2 < xt1)
     {
     mapxstep = -1;
     partial = (x1>>MAPBTOFRAC)&(FRACUNIT-1);
     ystep = FixedDiv ((int)(y2-y1),Math.abs((int)(x2-x1)));
     }
     else
     {
     mapxstep = 0;
     partial = FRACUNIT;
     ystep = 256*FRACUNIT;
     }

     yintercept = (int) ((_y1>>MAPBTOFRAC) + FixedMul (partial, ystep));


     if (yt2 > yt1)
     {
     mapystep = 1;
     partial = FRACUNIT - ((y1>>MAPBTOFRAC)&(FRACUNIT-1));
     xstep = FixedDiv ((int)(x2-x1),Math.abs((int)(y2-y1)));
     }
     else if (yt2 < yt1)
     {
     mapystep = -1;
     partial = (y1>>MAPBTOFRAC)&(FRACUNIT-1);
     xstep = FixedDiv ((int)(x2-x1),Math.abs((int)(y2-y1)));
     }
     else
     {
     mapystep = 0;
     partial = FRACUNIT;
     xstep = 256*FRACUNIT;
     }
     xintercept = (int) ((_x1>>MAPBTOFRAC) + FixedMul (partial, xstep));

    // System.out.printf("xstep %d ystep %d partial %d xintercept %d yintercept %d\n",xstep,ystep,partial,xintercept,yintercept);

     // Step through map blocks.
     // Count is present to prevent a round off error
     // from skipping the break.
     mapx = xt1;
     mapy = yt1;

     for (count = 0 ; count < 64 ; count++)
     {
     if (flags(flags ,PT_ADDLINES))
     {
         if (!BlockLinesIterator (mapx, mapy,AddLineIntercepts))
         return false;   // early out
     }

     if (flags(flags ,PT_ADDTHINGS))
     {
         if (!BlockThingsIterator (mapx, mapy,AddThingIntercepts))
         return false;   // early out
     }

     if (mapx == xt2
         && mapy == yt2)
     {
         break;
     }

     boolean changeX = (yintercept >> FRACBITS) == mapy;
     boolean changeY = (xintercept >> FRACBITS) == mapx;
     if (changeX) // _D_ there is a rare case when changeX and changeY are both true, that is why I modified this section
     {
         yintercept += ystep;
         mapx += mapxstep;
     }
     if (changeY)
     {
         xintercept += xstep;
         mapy += mapystep;
     }

     }
     // go through the sorted list
     //System.out.println("Some intercepts found");
     return TraverseIntercepts ( trav, FRACUNIT );
    } // end method