Use shortcut trace method to improve the ray trace efficiency

The most part of calculating time in the traditional ray trace method is on the intersection judgment, so upgrading on this process is the key to improve the main calculating efficiency. A technique named shortcut method was presented, based on the fact that most nearby rays take a same reflection trace. So one ray was really calculated and its trace called shortcut was recorded as the reference to give direction to the ray next to it. The overwhelming search for the intersecting point was avoided and the number of the really calculated rays was reduced a lot.