Drawing the linetrails following the hands

Now let's start to develop a very important part of our Fruit Ninja game: the knives that cut any coming fruits. Our hands can simulate the knives very well here, because in a motion-sense environment, they are always the most agile and accurate objects to operate on anything in space.

It will be easy to know the per-frame positions of the two hands as shown in the previous example. But it is also a good idea to add some trailing effects to demonstrate how fast and sharp the knives are, and to indicate to the players where their weapons are. In this example, we will emulate these trails with a series of continuous line segments. The alpha values of each line segment can also change so that the entire trail seems to fade out at the end.

Drawing the path for specified joints

To implement linetrails of two hands, we have to use a dynamic array to store historical points that the hands have moved to. We then connect them to implement the line-trail effect...