Our goal in this set of tutorials is to make a Motion particle system that simulates a natural snowfall. In this second tutorial, we will take a look at how the particle system Shape parameter will help us to accomplish our goal. To see the particle system parameters, we need to go to the Inspector.

In the previous tutorial, we converted a small circle shape into a particle system cell and emitter. When we played the default particle system animation, many duplicates of the small circle, called the Cell of the particle system, began moving over the screen around the original small circle’s position on the screen.

But we want to make an Apple Motion^R particle system that simulates a natural snowfall. So let’s take a look at one of the parameters we can change to accomplish our goal. To see the parameters, we need to go to the Inspector.

1. Select the Emitter layer in the Layers pane, and then click the Emitter tab in the Inspector. There you will see a list called Emitters Controls and under that is another list called Cell Controls.
   
   If you remember, the Cell is a duplicate of the small circle that we drew on the stage and the Emitter duplicates this Cell and runs the animation.
   
   Our animation is moving the small circles around a singular position on the screen, which doesn’t look much like a snowfall. This singular origination point on the screen is called a Point Emitter and is the default setting for the Shape parameter. The particles are emitted from this point on the screen.
   
   A Point emitter is just one option that we have for the Shape parameter. There are several Shape parameter options and each one gives us a different animation and set of related parameters.
   
   
2. In the Inspector, under Emitter Controls, open the Shape menu to see what other options that we have for our animation. Change the setting to each option in the menu, notice the parameters that go with that setting and play the animation. Each option gives us a different animation result on the screen.
   
   

For a snowfall animation, we will use the Line option for the Shape parameter.

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