Autodesk 62205-051408-9001 User Guide - Page 392

14 Creating Particle Effects Tracking an Emitter to a Clip After adding an emitter to a clip, a common task is to track it to a moving object in the clip. You do this using the Tracker, which is explained in Chapter 26, "Tracking''. To track an emitter object or control point: 1. Make the Particles operator the current operator. 2. Select the emitter object(s) in the viewport or Workspace panel. You can also select one or more control points of a line or deflector. 3. Show the Tracker (F6). Above the Clip list, the heading of the Tracker panel indicates the number of emitters or emitter control points (for lines or deflectors) that are selected. 4. Track as usual. See "Using the Tracker" in Chapter 26, "Tracking''. When a particle effect needs to be contained within a region, for example, you can use rotation tracking on an area emitter. Scale (size) tracking can also be used for area and circle emitters. Note: You cannot use rotation or scale tracking for point emitters. You cannot use scale tracking for line emitters. Simulating a Transform Manipulator When you want an outside force to manipulate the transforms of particles, you can modify the transforms of the layer instead. For example, to make wind affect a stream of smoke particles, you can make a motion path for the emitter in the Particles operator, then copy the keyframe data to the layer. After compensating for the difference in coordinate systems between the Particles and Composite operators, and reversing the data, the emitter remains stationary and the particles seem to blow in the wind. This keyframing trick also works for rotation. This transform only needs to be reversed for the layer; the Composite coordinate system does not affect rotation. You can also change keyframes using math operations. For example, you can add jitter and randomize them. Note: Before performing these steps, you should try animating the emission angle and other emitter properties, which is easier and may give the results you want. To simulate wind: 1. Create a solid layer in a composite with the Particles operator on it. Leave the layer at the center. 2. In the Particles operator, add an emitter. For example, add a point emitter that emits a short stream of smoke in one direction. Disable Speed, create a motion path for the emitter so it moves into the wind, then go to the first frame. Note: The effect must stay within the frame size; you can make the solid layer's footage larger if necessary. Note the frame size; you will need it in steps 6 and 9. 3. Double-click the Composite operator so it becomes the current operator. Disable Animate. 4. In the Timeline, select the X Position channel for the emitter. This selects all keyframes automatically. Copy the keyframes. 5. In the Workspace panel, select the layer. The Timeline updates to show the layer's channels. Select X Position and paste the keyframes. Do not deselect the keyframes yet. 376