FSO.SimAntics.VMArchitecture.RaycastWall C# (CSharp) Method

        public bool RaycastWall(Point p1, Point p2, sbyte level)
        {
            //Bresenham's line algorithm, modified to check walls
            //http://lifc.univ-fcomte.fr/home/~ededu/projects/bresenham/

            int i, ystep, xstep, error, errorprev, ddy, ddx,
                y = p1.Y,
                x = p1.X,
                dx = p2.X - x,
                dy = p2.Y - y;

            if (dy < 0)
            {
                ystep = -1;
                dy = -dy;
            }
            else
                ystep = 1;

            if (dx < 0)
            {
                xstep = -1;
                dx = -dx;
            }
            else
                xstep = 1;

            ddy = dy * 2;
            ddx = dx * 2;

            int xAOff = (xstep > 0) ? 1 : 0;
            int yAOff = (ystep > 0) ? 1 : 0;

            if (ddx >= ddy)
            {
                errorprev = error = dx;
                for (i = 0; i < dx; i++)
                {
                    int oldx = x;
                    int oldy = y;
                    x += xstep;
                    error += ddy;
                    if (error > ddx)
                    {
                        y += ystep;
                        error -= ddx;

                        //extra steps
                        if (error + errorprev < ddx)
                        {
                            //moved into x before y
                            if (GetWall((short)(oldx+xAOff), (short)(oldy), level).TopLeftSolid) return true;
                            if (GetWall((short)(x), (short)(oldy + yAOff), level).TopRightSolid) return true;
                        }
                        else
                        {
                            //moved into y before x
                            if (GetWall((short)(oldx), (short)(oldy + yAOff), level).TopRightSolid) return true;
                            if (GetWall((short)(oldx + xAOff), (short)(y), level).TopLeftSolid) return true;
                        }
                    }
                    else
                    {
                        //only move into x
                        if (GetWall((short)(oldx+xAOff), (short)(oldy), level).TopLeftSolid) return true;
                    }
                    errorprev = error;
                }
            }
            else
            {
                errorprev = error = dy;
                for (i = 0; i < dy; i++)
                {
                    int oldx = x;
                    int oldy = y;
                    y += ystep;
                    error += ddx;
                    if (error > ddy)
                    {
                        x += xstep;
                        error -= ddy;

                        //extra steps
                        if (error + errorprev < ddy)
                        {
                            //moved into y before x
                            if (GetWall((short)(oldx), (short)(oldy + yAOff), level).TopRightSolid) return true;
                            if (GetWall((short)(oldx+xAOff), (short)(y), level).TopLeftSolid) return true;
                        }
                        else
                        {
                            //moved into x before y
                            if (GetWall((short)(oldx+xAOff), (short)(oldy), level).TopLeftSolid) return true;
                            if (GetWall((short)(x), (short)(oldy + yAOff), level).TopRightSolid) return true;
                        }
                    }
                    else
                    {
                        //only move into y
                        if (GetWall((short)(oldx), (short)(oldy+yAOff), level).TopRightSolid) return true;
                    }

                    errorprev = error;
                }
            }
            return false;
        }