Speed Operator
 
 
 
Command entry:Particle View Click Speed in an event or add a Speed operator to the particle system and then select it.

This is the default Speed operator, which appears in the first event when you create a new Particle Flow icon. It provides basic controls over particle speed and direction.

Directional controls provided by the Speed operator are based on the position and orientation of the Particle Flow icon. For best results when using other objects as emitters, use the Speed By Surface Operator operator instead.

Procedures

Example: To change particles' speed:

The Speed operator works on an instantaneous basis: It sets each particle's speed once only, when it enters the event. Even if you animate the Speed value, each particle moves at a constant rate of speed, defined by the value at the time it enters the event. This procedure demonstrates a trick you can use to change particle speed with an animated Speed value, thanks to Particle Flow's looping ability.

  1. Create a default particle system, and position it at the top of the Perspective viewport.
  2. Play the animation.

    The particles fall downward at the default rate: 300 units per second.

  3. Add a Send Out test at the bottom of Event 01.
  4. Add a Speed operator to an empty area of the event display.

    This creates a new event.

  5. Turn on , and move the time slider to frame 30.
  6. In Particle View, click the new Speed 02 operator, and then in the Particle View parameters panel, set Speed to 0.

    This animates the Speed value from 300 at frame 0 to 0 at frame 30.

  7. Turn off .
  8. Wire the Send Out test in Event 01 to Event 02.
  9. Play the animation.

    The particles born later move slower, but all still move at a constant rate of speed.

  10. Add a Send Out test at the end of Event 02.
  11. Create a new event using an Age Test. Click the Age Test to display its parameters, and then set the following:
    • Event Age
    • Test Value=1
    • Variation=0
  12. Wire the Send Out test in Event 02 to Event 03.
  13. Wire the Age Test in Event 03 to Event 02.
  14. Play the animation.

    All the particles slow down simultaneously and eventually come to a stop.

    Here's how it works: As each particle enters Event 02, its speed is set to the current Speed value in the Speed operator. Particle Flow then sends the particle immediately to Event 03, where it sits for one frame. Event 03 then returns the particle to Event 02, whose Speed value is now lower. Particle Flow perceives the returned particle as newly entering the event, so it changes its speed to the current Speed value. Thus, the particles continually return to Event 02 one frame later than before, and are assigned a progressively lower speed.

    If you wanted the particles to do something else after they stop, you could add a Speed Test to Event 02, above the Send Out test, set Test True If Particle Value to Is Less Than Test Value, and set Test Value to a very low value, such as 0.01. Then wire the Speed Test to a different event.

Interface

The user interface appears in the parameters panel, on the right side of the Particle View dialog.

Speed

The particle speed in system units per second. Default=300.

A positive Speed value moves the particles in the direction determined by the Direction setting; a negative Speed value moves the particles in the opposite direction.

NoteSpeed sets each particle's speed once only: when the particle enters the event (or is born, in the case of a birth event). If you animate the Speed value, particle speed does not vary: rather, each particle is given a constant speed equal to the current Speed value when it enters the event.
Variation

The amount by which particle speed can vary, in system units per second. Default=0.0.

To obtain each particle's speed, the system multiplies the Variation value by a random number between -1.0 and 1.0, and then adds the result to the Speed value. For example, if Speed=300 and Variation=100, then each particle's speed would be between 200 and 400.

Direction group

The Direction drop-down list lets you specify which way the particles go after they're born. Default=Along Icon Arrow. In most cases, the actual direction also depends on the icon orientation. The primary exception is when Position Location is set to Pivot.

Particle movement is always in a straight line unless influenced by other factors.

Along Icon Arrow

Particles move parallel to the icon arrow. Rotate the icon to change the direction.

Icon Center Out

Each particle moves along an imaginary line drawn between the particle's location and the icon center.

With the flat icon types (Rectangle and Circle), this results in all the particles moving in one plane, unless you increase Divergence above 0.0. With icons that have height (Box and Sphere), the particles move outward in three dimensions.

Particles at the center, as is the case when the Position operator's Location parameter is set to Pivot, arbitrarily move along the world X axis.

Icon Arrow Out

Each particle moves along an imaginary line drawn between the particle's location and the icon arrow. The line is perpendicular to the icon arrow, which is considered an infinite line for this purpose.

With the flat icon types (Rectangle and Circle), this results in all the particles moving in one plane, unless you increase Divergence above 0.0. With icons that have height (Box and Sphere), the particles move outward in a cylindrical formation.

Random 3D

Particles move in all directions. This option is affected by the Uniqueness setting.

Random Horizontal

Each particle moves in a random horizontal direction; that is, parallel to the world XY plane. This option is affected by the Uniqueness setting.

Inherit Previous

Uses the current direction of motion.

If you choose Inherit Previous but no direction was previously specified, the speed and direction are undefined; the particles don't move.

Reverse

When on, the direction is reversed. Default=off.

Using Reverse is the equivalent of multiplying the Speed value by -1. This option is unavailable if Random 3D or Random Horizontal is chosen.

Divergence

When on, spreads out the particle stream. Use the numeric setting to define the extent of the divergence, in degrees. Range=0 to 180. Default=0. The value can be animated.

This option is unavailable if Random 3D is chosen.

TipFor a fountain-like spray, set Position Location to Pivot, set Direction to Along Icon Arrow, set Divergence to the desired angle, and rotate the icon so its arrow points upward.

Uniqueness group

The Uniqueness setting enables randomization of speed variation, and randomization of direction with the Random 3D and Random Horizontal options.

Seed

Specifies a randomization value.

New

Calculates a new seed using a randomization formula.

See Also