An emitter is where all particle effects begin, specifying where the particles appear and affecting their initial trajectory.
A default emitter is added automatically to a new particle simulator, but this can be deleted if you wish.
Shape
Emitters can be several shapes. You can choose the emitter shape using the Shape menu. Clicking on any shape properties will display a wireframe outline of the shape in the Viewer.
- Each shape has its own properties to define its size and position.
- Shapes can be attached to another layer in the same composite shot, such as a point layer. The emitter will then animate to stay in the same relative position to the parent layer.
- The Boundary option forces particles to only be birthed around the edge of the shape, rather than inside the shape.
Grid
Activating the Grid option restricts particle birth to specific grid positions. This is useful for creating more regimented patterns, for motion graphics purposes or even controlled clusters of 3D textures (eg buildings arranged into city blocks).
The grid will always fill the specified emitter shape. The number of available grid positions can be defined in all three dimensions, which will then be evenly distributed within the emitter shape.
The Avoid previous positions option will force particles to spawn on a previously unused grid position until all available positions have been occupied.
Shape layers
If you set your emitter shape to a layer you access additional settings.
Use Layer Color uses the source to color the particles. This is a highly effective way to create a range of color within a particle effect and can be used to blend particles in with the source.
Use Layer Alpha uses the alpha channel in the source to define where the particles are born. The Threshold is then used to adjust the minimal alpha value required for particle birth. This makes it possible to confine an emitter to a specific shape, such as a green screen actor or a custom gradient.
Trajectory
When particles are birthed they need an initial trajectory, to determine which direction they move in.
- Cone – emit in a funnel shape.
- Explode – emit in a direction away from the center of the shape.
- Implode – emit in a direction towards the center of the shape.
- Disc – emit in a flattened disc shape.
- Random – emit in random directions.
- Target – emit particles towards a specified 3D point.
Expanding the Trajectory group will give you access to the controls for your selected trajectory.
General
The General group contains a single Active property. This turns the emitter on and off and is used for controlling the visibility of all existing particles.