Line Raycast with Blocks

import java.util.function.BiConsumer;

import static java.lang.Math.floor;

public class RaycastUtil {

    public enum Face {
        UP, DOWN, FRONT, BACK, RIGHT, LEFT;

        @Override
        public String toString() {
            return name();
        }
    }

    public static double fceil(double n) {
        return Math.floor(n) + 1.0;
    }



    //http://www.cse.yorku.ca/~amana/research/grid.pdf
    public static void line3D(double startX, double startY, double startZ, double endX, double endY, double endZ, BiConsumer<Vector3d, Face> callback) {
        //Block's cordinates
        int rx = (int) floor(startX);
        int rex = (int) floor(endX);
        int ry = (int) floor(startY);
        int rey = (int) floor(endY);
        int rz = (int) floor(startZ);
        int rez = (int) floor(endZ);


        if(rx == rex && ry == rey && rz == rez) {
            callback.accept(new Vector3d(rx, ry, rz), null);
            return;
        }

        double dx = endX - startX;
        double dy = endY - startY;
        double dz = endZ - startZ;

        int stepX = (int) Math.signum(dx);
        int stepY = (int) Math.signum(dy);
        int stepZ = (int) Math.signum(dz);

        double tMaxX = dx == 0 ? Double.POSITIVE_INFINITY : (fceil(startX) - startX) / dx * stepX;
        double tMaxY = dy == 0 ? Double.POSITIVE_INFINITY : (fceil(startY) - startY) / dy * stepY;
        double tMaxZ = dz == 0 ? Double.POSITIVE_INFINITY : (fceil(startZ) - startZ) / dz * stepZ;

        double tDeltaX = tMaxX * dx * stepX;
        double tDeltaY = tMaxY * dy * stepY;
        double tDeltaZ = tMaxZ * dz * stepZ;

        final Face faceX = stepX > 0 ? Face.LEFT : Face.RIGHT;
        final Face faceY = stepY > 0 ? Face.DOWN : Face.UP;
        final Face faceZ = stepZ > 0 ? Face.FRONT : Face.BACK;

        callback.accept(new Vector3d(rx, ry, rz), null);

        do {
            Face face;
            if(tMaxX < tMaxY) {
                if(tMaxX < tMaxZ) {
                    tMaxX += tDeltaX;
                    startX += stepX;
                    rx += stepX;
                    face = faceX;
                } else {
                    tMaxZ += tDeltaZ;
                    startZ += stepZ;
                    rz += stepZ;
                    face = faceZ;
                }
            } else {
                if(tMaxY < tMaxZ) {
                    tMaxY += tDeltaY;
                    startY += stepY;
                    ry += stepY;
                    face = faceY;
                } else {
                    tMaxZ += tDeltaZ;
                    startZ += stepZ;
                    rz += stepZ;
                    face = faceZ;
                }
            }

            callback.accept(new Vector3d(rx, ry, rz), face);
        } while(!(rx == rex && ry == rey && rz == rez));
    }
}