In the previous tutorial, we examined the Shape parameter, which controls the emission area for our snowfall particle system. From the various options, we decided to use the Line option for the Shape parameter to create our snowfall.

1. Continuing to work in the Inspector, set the Shape parameter menu to Line.
   
   This will tell Motion to use a line as the emission point for our snowfall animation. Each new snowflake cell will begin life, ie be placed on the screen, somewhere along this line, which makes our animation more realistic. But this line is a little small and the snowfall is still originating from the center of the screen. Let's widen the Line Emitter to cover the entire screen.
   
   
2. Expand the Start Point and End Point parameter settings to reveal the default settings.
   
   As you can see, our line, which is invisible on the Canvas, begins at -100 pixels from the original Point location and ends at 100 pixel from the Point. So the Emitter will add snowflakes to the screen anywhere along this 200 pixel invisible line.
   
   Now, the snowflakes are emitting along this line and from the top, bottom and sides of the line. Snowflakes don't fall upward and we want them to cover the entire Canvas, so let's make another adjustment.
   
   We can widen the line from which our snowflakes emit to cover the entire Canvas. One way to do this is to adjust the Start and End Points for our Line emitter. With the circle still at the center of the Canvas we can move the end points to extend beyond the edge of the canvas on both sides, using controls in the Inspector.
   
   
3. Using the slider controls for the Start Point, set the value to -1000. Repeat this step for the End Point, using the slider to set the value to 1000.
   
   

Let the animation play for about 2 seconds and notice that the snowflakes will cover the entire width of the stage because the Line emitter extends beyond the edges. But the snowflakes are still traveling outward from the top, bottom and sides of the line. Our next step is to make all the snowflakes fall in one direction, downward. We can do this by changing the Emission Range and Emission Angle for the Line emitter, in the Inspector. But let's open the HUD (Windows - open HUD) to see what happens there as we make changes in the Inspector.

As you can see, the HUD has controls for the Birth Rate, Life, Scale and Emission Range. The Emission Range has a 360 degree control slider. When working in 2D, the Emission Range control in the HUD will control both the Emission Range and Emission Angle, which controls the direction of the moving particles. But in the Inspector, we have a separate control for each.

Let's continue to work in the Inspector.

Note: In this tutorial, we are working in 2D. When we work in 3D, we have even more choices for the Shape parameter including Depth Ordered, Emission Longitude, Emission Latitude and Render Particles.

Tutorial Example:


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