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In Part I, we used a fairly simple system of particles to throw footballs across the screen. In that process, we explored the basic controls that Motion offers over its point-based particle emitters: emission angle, range, particle speed and angle, and so forth.

This time, we'll work up an effect something like a primitive snow flurry. That will let us go over shape-based emitters, evolve particles over their lifetimes, and touch on physics simulations.

Background

By default, your particle system emits from a single point -- that is, it "throws" out each new particle from the same initial position. But sometimes, you'd like to generate particles from random points in a given region. For example, consider a "falling leaves" system: you want the leaves to drop down from random positions across the top of the screen. Or consider a starfield system: you want twinkling stars to be born in random places across the entire sky (and not move at all, probably). In the Emitter Inspector, Motion provides nine different Shape options for your emitter, ranging from single points to lines, rectangular regions, and even spirals. If you place your emitter in 3D mode, you'll have two extra Shapes at your disposal (Cube and Sphere).

The specific shapes are beyond the scope of this tutorial (drop me a line if you want a blog on each one), but if you want to play around with them, be sure you have Overlays turned on in your Canvas. Then, use the Adjust Object tool to show the actual shape of the emitter in your Canvas.

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Also, we'll be using "Over Life" controls. For today, we'll stick to the default cell evolution parameters, which you can find in your emitter's Emitter Inspector under Color Mode (later in the series, we'll also use Scale Over Life and Spin Over Life behaviors from the Particle Behaviors menu; they work similarly to the Color-related evolution parameters).

Basically, we're asking each individual particle to change in specific ways over its own, individual lifetime. Recall that, by using the "Cell Life" parameter, we have specified that each particle is on screen for a certain amount of time before it disappears ("dies"). All of these "Over Life" behaviors work on a per-cell basis using that cell's birth and death times. Each "Over Life" control will give you either a graph or a color bar to customize: whichever control you're using, the left side of that control corresponds to the frame where the cell is born, and the right side corresponds to when the cell dies. For example, imagine that we're using an Opacity Over Life control to affect a cell with a lifespan of 150 frames.

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Now, as each cell is thrown out from the emitter, it starts out invisible. Over the next 10 frames, it fades to a medium opacity, then it gradually fades up to full opacity over the next 80 or so frames. Finally, it begins a long fade out, which finishes as the particle "dies" and leaves the screen. This process can be useful for a lot of purposes, from shaping flames to simply avoiding the jerky look of emitters that spit out full-opacity particles.

Finally, we'll apply a physics simulation to today's particle system. Located in the Simulations category of the Behaviors, this group of behaviors will (by default) affect each individual particle independently. In today's example, we'll throw a local Vortex into our world to simulate a little pile of snow on the "ground" (disclaimer: I'm from Florida, so I don't exactly know much about real snow). But I strongly encourage you to play with these simulations: they're an incredibly painless way to add relatively sophisticated motion to otherwise boring comps (and particle systems). Plus, some of the simulations allow your particles to interact with other, probably-more-important elements of your scene (like your primary shots or titles).


Step-By-Step

  1. We've got snow on our minds, so let's start with a snowflake. The closest element in your Motion Library is probably in the Content category, under Particle Images, called "texture 01." Drag it to the center of your Canvas.
  2. While the "snowflake" is selected, click the orange Make Particles button on top of your Canvas.
  3. The default emitter type is a point emitter, but we want snow to fall down randomly from the top of the Canvas. In the Emitter Inspector, change the emitter's Shape from Point to Line.
    ps2-4.png
  4. You'll notice that ... well, nothing much has changed over in your Canvas. In order to adjust the shape of the emitter, you'll want to use the Select/Transform Tool (the half-arrow tool; keyboard shortcut is S). Stretch the line emitter to the width of the Canvas, and move it above the Canvas. As you scrub through your timeline, you should see "snowflakes" falling fairly uniformly across your screen.
    ps2-5.png
    ps2-6.png
  5. Adjust the basic parameters of the particle system so that different snowflakes have different angles, spins, and scales. If you're confused about these settings, you may want to revisit Part 1 of this series. If you'd like, copy my settings from below:
     ps2-7.png
    ps2-8.png
  6. Now, let's affect the snowflakes' opacity over the course of their lives. I've chosen to have the snowflakes fade from completely invisible to a medium opacity, then gradually get more visible before fading out. I encourage you to play around. To add a point to the gradient, click inside the gradient. You'll get a little square at the point where you clicked, and you can adjust the opacity at that point by using the slider below the control. You can shift boxes back and forth simply by clicking and dragging, and you can get rid of boxes by dragging them out of the gradient (you'll see a little "poof" effect when you do).
    ps2-10.png
  7. Finally, let's experiment with some Simulation behaviors. You can see a couple of approaches to animating snow in Motion's Library, with the Snow Flurry and Snow Blizzard particle emitter presets; but today we'll go more for the tacky animated-Christmas-card effect, piling up the snow at the bottom of the screen. We want to affect the individual particles, so apply these behaviors to the particle itself, not the emitter (see first screen capture below). First, apply an Edge Collision behavior (Add Behavior --> Simulation --> Edge Collision), and make yours look more or less like mine:
    ps2-11.pngps2-12.png
  8. As you scrub your timeline, you'll notice that while the snow does indeed stick to the bottom of the screen, the flakes continue to scamper around when they hit the ground. While we can't directly control the friction of the edge, we can apply some drag to the individual particles so that their horizontal drift calms down before they hit the ground. Apply a Drag Behavior to the particles. By default, the drag will work in all dimensions, causing the snow to stop before it hits the ground: untwirl the Amount disclosure triangle, and make sure the drag is only applying in the X dimension.
    ps2-13.png

Next time, we'll attach a flame particle system to the exhaust pipe of a motorbike, and have it respond to an engine-revving sound effect. In the process, we'll use a tracker with our emitter, learning about offset and emitter-affinity controls; we'll also parameterize our emitter in relation to the audio's amplitude.

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Soundtrack Pro 3's new Feature Easy Audio Restoration was the previous entry in this blog.

Apple Compressor Droplet For Multiple Settings is the next entry in this blog.

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