Emitter and Cell Parameters

Several parameters in the Emitter tab are identical to those found in the Emitter HUD, with one difference. While the emission control in the Emitter HUD allows you to manipulate the Range, Angle, Latitude (3D), Longitude (3D), and Speed parameters using a single, graphical control, the Emitter tab uses individual controls for each parameter.

Figure. Inspector showing individual controls representing the HUD's graphical emission control.

Note: There is no way to directly control the animation of individual particles.

Important: The emitter parameters in the Properties and Emitter tabs can be keyframed to change values over time.

Emitter Parameters in the Inspector

These parameters determine how particles are distributed and rendered in your project. The Emitter tab of the Inspector has a large number of parameters, some of which depend on how certain parameters are set within the tab itself. All the various combinations of parameters are described below.

  • Size: This parameter is available when Rectangle or Box is chosen in the Shape pop-up menu. Defines the size of the rectangle or cube from which particles are emitted. This parameter is available whether the Arrangement is set to Outline, Tile Fill, or Random Fill. When Rectangle is the selected shape, the Width and Height parameters are available. When Box is selected, an additional Depth parameter is available.

    Note: The Height is measured in project pixels; however, the Width is measured in square pixels. This is done so that a shape that is numerically square will look square when Correct for Aspect Ratio is turned on (checkmarked) in the View pop-up menu in the top-right corner of the Canvas.

  • Columns: This parameter is available when one of the following is chosen in the Shape pop-up menu: Rectangle, Circle, Image, Box, or Sphere; in addition, Arrangement must be set to Tile Fill. This parameter specifies the number of horizontal emitter points on a grid over the selected emitter shape. In the case of an irregular shape (nonrectangular), grid points that fall outside of the shape are ignored.
  • Rows: This parameter is available when one of the following is chosen in the Shape pop-up menu: Rectangle, Circle, Image, Box, or Sphere; in addition, Arrangement must be set to Tile Fill. This parameter specifies the number of vertical emitter points on a grid over the selected emitter shape. In the case of an irregular shape (nonrectangular), grid points that fall outside of the shape are ignored.
  • Ranks: This parameter is available when Box or Sphere is chosen in the Shape pop-up menu and Tile Fill is the selected Arrangement. This parameter specifies the number of points in Z space on a grid over the selected shape from which particles are emitted.
  • Tile Offset: This parameter is available when one of the following is chosen in the Shape pop-up menu: Rectangle, Circle, Image, Box, or Sphere; in addition, Arrangement must be set to Tile Fill. Values from 0 to 100% offset the rows toward the right, and values from 0 to –100% offset the rows toward the left. A value of 50 or –50% creates a “brickwork” pattern.
  • Image Source: This parameter is available when Image is chosen in the Shape pop-up menu, and lets you specify the object used to define the shape of the emitter. Any image or movie clip can be dropped onto this well to assign the desired shape.
  • Shape Source: This parameter is available when Shape is set to Geometry. This image well allows you to specify an object that defines the shape of the emitter. Spline objects may be dropped onto this well to assign the desired shape.
  • Emission Alpha Cutoff: This parameter is available when Image is chosen in the Shape pop-up menu. When the Image Source object contains an alpha channel, this slider defines the minimum opacity value that is necessary to create particles at that point on the source image. For example, when set to 25%, particles appear only where the alpha value of the image is equal to or greater than 25% opacity. The lower the Emission Alpha Cutoff value, the more particles appear. In order for this parameter to be effective, the alpha channel needs to have areas of varying transparency.
  • Start Point: This parameter becomes available when Shape is set to Line or Wave. Two sliders that define, in X and Y coordinates, the first point of the line used as the emitter shape. Click the disclosure triangle to modify the Z position of the start point. You can adjust these values in the Canvas using the onscreen controls (with the Adjust Item tool).
  • End Point: This parameter becomes available when Shape is set to Line or Wave. Two sliders that define, in X and Y coordinates, the second point of the line used as the emitter shape. Click the disclosure triangle to modify the Z position of the start point. You can adjust these values in the Canvas using the onscreen controls (with the Adjust Item tool).
  • Emit At Points: This checkbox is available when any of the following is chosen in the Shape pop-up menu: Line, Rectangle (with Arrangement set to Outline or Random), or Circle (with Arrangement set to Outline or Random), Burst, Spiral, Wave, Geometry, Box (with Arrangement set to Outline), Sphere (with Arrangement set to Outline). When the Emit At Points checkbox is selected, particles emerge from a limited number of points (as defined in the Points parameter). When the checkbox is deselected, particles may emerge from anywhere on the line or edge. When the Adjust Item tool is selected, the points are visible in the Canvas. When Emit At Points is selected, two additional parameters become available: Point and Offset.
  • Points/Points Per Arm: This parameter is available when any of the following is chosen in the Shape pop-up menu: Line, Rectangle, Image, or Circle (with Arrangement set to Outline or Random Fill), Burst, Spiral, Wave, or Geometry; in addition, the Emit At Points checkbox must also be selected. Defines the number of points from which particles are emitted. For Rectangle or Circle shapes, the particles are emitted from evenly distributed points along the edge of the shape when Outline is chosen from the Pattern pop-up menu. When the Adjust Item tool is selected, the points are visible in the Canvas.

    Keep in mind that using a large number of points slows your computer’s processing time.

  • Radius: This parameter is available when one of the following is chosen in the Shape pop-up menu: Circle, Burst, Spiral, or Sphere. Defines the size of the shape from which particles are emitted.
  • Twists: This parameter, available when Spiral is chosen in the Shape pop-up menu, defines the number of turns in the spiral. The default value is 0.25.
  • Number of Arms: This parameter, available when Burst or Spiral is chosen in the Shape pop-up menu, defines the number of branches from which particles are emitted. The default value is 3.
    Figure. Canvas window showing a Spiral emitter with modified Twists setting.
  • Amplitude: This parameter, available when Wave is chosen in the Shape pop-up menu, defines half the distance from the highest point to the lowest point in the wave. Higher values result in more extreme waves.
  • Frequency: This parameter, available when Wave is chosen in the Shape pop-up menu, defines the number of waves. Higher values result in more waves.
  • Phase: This parameter, available when Wave is chosen in the Shape pop-up menu, defines the degrees of the offset of the waves from the start and end points of the path. When set to 0 degrees (default), the wave begins and ends at half the distance from the highest point to the lowest point in the wave. When set to 90 degrees, the wave begins and ends at the highest point in the wave. When set to 90 degrees, the wave begins at the lowest point in the wave. When set to 180 degrees, the waves are the same as 0 degrees, but inverted.
  • Damping: This parameter, available when Wave is chosen in the Shape pop-up menu, determines the direction of progressive diminishment of the oscillation of the wave. Positive damping values diminish the wave forward (from left to right); negative values diminish the wave backward (from right to left).
  • Offset: This parameter is available when any of the following is chosen in the Shape pop-up menu: Line, Rectangle (with Arrangement set to Outline), Circle (with Arrangement set to Outline), Burst, Spiral, Wave, Geometry, or Image. Offsets either the emitter itself or the particles generated on the shape. For example, when the emitter Shape is a Line, changing the Offset value moves the emitter’s position in the Canvas. When the emitter Shape is a Rectangle and Pattern is set to Outline, changing the Offset value moves the particles along the edge of the shape.
  • 3D: When this checkbox is selected, the 3D emitter shapes (Box and Sphere) become available. Because all emitter shapes can be used in 3D space, additional 3D parameters are available for all emitter shapes when the 3D checkbox is selected: Render Particles, Emission Latitude, and Emission Longitude. These additional parameters appear in the Emitter Inspector and HUD.

    These parameters are available for all shapes, regardless of the Arrangement setting.

    Note: When the 3D checkbox is selected, particles cannot receive reflections and the Reflections parameter (in the Properties tab) is no longer available for the emitter. Additionally, when the 3D checkbox is selected, In Global 3D (Better) must be selected from the Render Particles pop-up menu in order for particles to cast shadows and to be affected by lights.

    For more information on the additional 3D controls in the HUD, see. Emitter HUD Parameters.

  • Emission Angle: This parameter is only available when Shape is set to a 2D shape. This dial sets the direction in which particles travel. This parameter works in conjunction with the Emission Range parameter. It is equivalent to one of the functions of the graphical emission control in the Emitter HUD.

    Note: When using an emitter shape other than a Point, such as a Line, Circle, Rectangle, Spiral, Burst, or Wave, and Outline is chosen from the Arrangement pop-up menu, setting the Emission Angle parameter to 180 degrees and the Emission Range parameter to 0 degrees restricts the emission of particles to the inside of the shape. Setting the Emission Angle parameter to 0 degrees and the Emission Range parameter to 0 degrees restricts the emission of the particles to outside of the shape.

  • Emission Range: A dial that restricts the area around the center of each emission point from which particles are generated, in the direction of the Emission Angle. It is equivalent to one of the functions of the graphical emission control in the Emitter HUD.

    Note: When using a Line, Circle, Rectangle, Spiral, Burst, or Wave (but not Geometry) shape, setting the Emission Range parameter to 0 degrees keeps particles perpendicular to the emitter when they emerge.

  • Emission Latitude: Available when 3D is turned on, this control specifies the emission direction (in degrees latitude) of the particles.
  • Emission Longitude: Available when 3D is turned on, this control specifies the axis of rotation (in degrees longitude) from which the particles are emitted.
  • Depth Ordered: Available when 3D is turned on. When activated, this checkbox draws the particles in the particle system according to each particle’s actual 3D position in the project. In other words, particles that are closer to the camera appear closer; particles that are farther away from the camera appear more distant.
    Figure. Canvas showing particle system with the Depth Ordered setting on, and with the setting off.
  • Face Camera: A checkbox that becomes available when 3D is turned on. When activated, the particle system always faces the active scene camera. For more information on cameras, see Active Camera.
  • Interleave Particles: Turning this checkbox on mixes particles generated from multiple cells together. Turning this checkbox off layers particles in the same order as the cells that generate them.

    Note: This option has no effect with particle systems containing only one cell. Leaving this option off speeds rendering with multiple cells.

Particle Cell Parameters in the Inspector

The following parameters apply to the creation and motion of the individual particles generated by each cell within an emitter. Cell Controls appear at the bottom of the Emitter tab of the Inspector when a particle system is selected, and in the Particle Cell tab of the Inspector when a particle cell is selected.

Figure. Inspector showing Particle Cell tab.
  • Birth Rate: A slider that defines the birth rate of the cell. In other words, this parameter defines how many particles of this cell emerge from the emitter every second. Higher values create denser particle effects.
    Figure. Canvas window showing a particle system with low and with high birth rate.
  • Birth Rate Randomness: A slider that defines an amount of variance in the Birth Rate of generated particles. A value of 0 results in no variance—particles emerge from the emitter at the same rate. A value greater than 0 introduces a variance defined by the Birth Rate parameter, plus or minus a random value falling within the Birth Rate Randomness.
  • Initial Number: A slider that defines the initial number of particles. This parameter determines how many particles of this cell appear at the first frame of a particle effect. The result is an initial burst of particles that eventually evens out according to the Birth Rate parameter.
    Figure. Canvas window showing effect of Inital Number setting.
  • Life: A slider that defines the duration of every particle, in seconds. This parameter specifies how long each particle lasts before vanishing from existence. This effect is similar to how sparks disappear after flying away from a sparkler. Unless the Color Over Life parameter or Opacity Over Life parameter is used to fade each particle out over its life, particles immediately vanish at the end of their lifetimes.
    Figure. Canvas window showing effect of Life parameter.
  • Life Randomness: A slider that defines an amount of variance in the life of generated particles. A value of 0 results in no variance—all particles from the selected cell emerge with the same lifetime. A value greater than 0 introduces a variance defined by the Life parameter, plus or minus a random value falling within the Life Randomness.
  • Speed: A slider that defines initial speed. This parameter determines how quickly each particle flies away from the emitter. This, in conjunction with the Life and Birth Rate parameters, determines how many particles appear in the Canvas at any given frame. It is equivalent to one of the functions of the graphical emission control in the HUD.
  • Speed Randomness: A slider that defines an amount of variance in the speed of generated particles. A value of 0 results in no variance—all particles from the selected cell emerge with the same speed. A value greater than 0 introduces a variance defined by the Speed parameter, plus or minus a predetermined random value falling within the Speed Randomness.
  • Align Angle: When selected, the particles automatically rotate to match the shape on which they are positioned. This parameter is available in all cases but the following: Rectangle, Circle, Image, Box, and Sphere shapes with Tile Fill or Random Fill and Point.
  • Angle: A dial that defines the angle of rotation, in degrees, at which new particles are created.
  • Angle Randomness: A dial that defines an amount of variance in the angle of generated particles.
  • Spin: A dial that animates particles in a system by initially spinning each individual particle around its center. Adjustments to this control are in degrees per second.
  • Spin Randomness: A dial that defines an amount of variance in the spin of generated particles. A value of 0 results in no variance—all particles from the selected cell spin at the same rate. A value greater than 0 introduces a variance defined by the Spin parameter, plus or minus a random value falling within the Spin Randomness.
  • Additive Blend: By default, particles are composited together using the Normal blend mode. Select this checkbox to composite all overlapping generated particles together using the Additive blending mode. This blending occurs in addition to whichever compositing method is already being used. The result is that the brightness of overlapping objects is intensified. This effect applies only to the particle system itself—the blend mode of the emitter determines how the result of the emitter is blended into the scene.
    Figure. Canvas window showing effect of Additive Blend setting.
  • Scale: A slider that defines the scale of every particle of a cell. Click the disclosure triangle next to the Scale parameter to reveal separate X and Y scaling subparameters, which can be used to resize the width and height of generated particles. This control affects the initial scale of the particle (compared to the Scale Over Life behavior in the Particles behavior category).
    Figure. Canvas window showing effect of Scale parameter.

    Note: When you use an image as a particle cell source and set a low Scale value, it is recommended that you set the render quality in the Render pop-up menu (in the Status Bar) or the View menu to Best (choose View > Quality > Best).

  • Scale Randomness: A slider that defines an amount of variance in the scale of generated particles. A value of 0 results in no variance—all particles from the selected cell emerge with the same size. A value greater than 0 introduces a variance defined by the Scale parameter, plus or minus a random value falling within the Scale Range. The disclosure triangle of the Scale parameter reveals separate X and Y subparameters, which can be used to set the width and height of the Scale Range separately.
  • Attach To Emitter: A slider that determines how closely particles follow the position of a moving emitter. If set to zero, particles follow their own path after being emitted, resulting in particles that trail along the motion path the emitter is following. If this parameter is set to 100, in the absence of other behaviors, all generated particles follow along with the emitter, surrounding it in a moving cloud of particles.
    Figure. Canvas window comparing particle system with Attach To Emitter set to a low value versus a high value.
  • Play Frames: This parameter appears if the particle system was created from a QuickTime movie. This checkbox controls playback. If selected, playback of the animation or movie clip used to generate each particle loops. If deselected, particles are generated using the still frame specified by either the Random Start Frame parameter or the Source Start Frame parameter.
  • Random Start Frame: This checkbox appears if the particle system was created from a QuickTime movie. Introduces variation into animated particles generated from QuickTime objects. If selected, each newly generated particle begins at a different frame of the animation. Stills are chosen randomly if Play Frames is deselected.
  • Source Start Frame: This parameter appears if the particle system was created from a QuickTime movie. Chooses the frame to begin animation, if the Play Frames checkbox is selected, or the still frame to display if Play Frames is deselected. This parameter only appears if Random Start Frame is deselected.
  • Hold Frames: This parameter appears if the particle system was created from a QuickTime movie. Adjust the slider to change the number of times each frame of the source movie is repeated during playback. The larger the Hold Frames value, the slower your playback.
  • Hold Frames Randomness: This parameter appears if the particle system was created from a QuickTime movie. Varies the number of frames to “hold.”
  • Random Seed: Although particle systems seem random, they’re actually deterministic. This means that the random variation in each particle system is created based on the number shown here. Unless this seed number is changed, a particle system with the same parameter settings always plays back with the same motion. If you don’t like the current random motion or distribution of the particle system, you can change the seed number by typing a new number or clicking Generate. This changes the random calculations performed for that system for all randomness parameters.

    For more information about the random nature of particle systems, see The Predictability of Particle Systems.

  • Particle Source: In particle systems with more than one cell, a parameter representing each cell appears at the bottom of the Emitter tab. Each cell parameter has a checkbox you can use to enable or disable that cell, a name field, and an image well for that object.