Shape Facing Operator

The Shape Facing operator creates each particle as a rectangle that always faces a particular object, camera, or direction. For effects like smoke, fire, water, bubbles, or snowflakes, use Shape Facing with a material containing appropriate opacity and diffuse maps.

• Particle View > Click Shape Facing in an event or add a Shape Facing operator to the particle system and then select it.

By default, the particles' top and bottom sides are parallel to the horizontal plane. The Orientation setting lets you change this default alignment.

Note: For the Shape Facing operator to be able to calculate the particle orientation, it must know the current particle position. For this reason, always place the Shape Facing operator below a Position operator in an event.

Interface

Look At Camera/Object group

Use this control for defining the camera or object toward which the particle will face. This object is known as the Look At object. For the technically minded, the facing is maintained by keeping each particle's local Z axis pointed at the Look At object, or when Use Parallel Direction is on, aligned with the vector between the Particle Source icon and the Look At object.

Name

After picking a Look At object, its name appears here.

Pick Camera or Object

Click this button, and then select a camera or object in the scene to use as the Look At object. The mouse cursor changes to a cross shape when positioned over a valid object.

Use Parallel Direction

When off, all particles continuously rotate to stay facing toward the Look At object. Each particle's orientation varies because its location differs from those of the others. When on, all particles face in the same direction, defined by an imaginary line between the Particle Source gizmo center and the Look At object. Default=off.

Size/Width group

Use these settings to specify the coordinate system for setting the size, as well as the size parameters. The numeric settings in this group are not animatable.

• In World Space Sets the absolute size in system units, using the World coordinate system.

  Units With the In World Space option, sets the particle size in system units. Range=0 to 1000000000. Default=1.

• In Local Space Sets particle size relative to the existing size, in local space. Particle Flow uses the dimensions of the existing shape to determine the size of the “facing rectangle.”

  Inherited % Sets the facing particles' size as a percentage of the existing size. Range=0 to 100. Default=100.

• In Screen Space Sets the facing particles' size as a percentage of the screen width. The actual size of each particle changes as necessary throughout the animation, depending its distance from the camera, to maintain a constant size from the camera's point of view.

  This option is available only when the Look At object is a camera, and Use Parallel Direction is off.

  Proportion % Sets the particle size as a percentage of the screen width. Default=1.

  Variation % Sets the percentage by which particle size can vary. Default=0.

Pivot At

Specifies the part of the particle around which rotation is performed when maintaining the facing direction. The choices, available from the drop-down list, are Top, Center, and Bottom. Default=Center.

With Top and Bottom, the center of the corresponding side is used as the particle center for rotation.

This option is useful, for example, when particles are lying on a surface, and each particle is an explosion. In this situation, you'd probably want the entire particle rectangle to appear above the surface, so you'd set Pivot At to Bottom.

W/H Ratio

Defines the aspect (width-to-height) ratio of the shape rectangle.

Adjust this ratio to that of the particle-map imagery. For the commonly used TV aspect ratio of 4:3, set W/H Ratio=1.33. The parameter is not animatable. Range=0.001 to 1000. Default=1 (square particles).

This value is not animatable.

Orientation group

Use this drop-down list to choose how particles rotate on the axes not specified by the Look At direction.

• Align to Horizon (The default.) Keeps the top edge aligned with the horizon (the world XY plane).
• Align to Speed Follow Uses the right side of each particle as the leading edge, so the top and bottom edges are aligned with the direction of particle motion.
• Random Orients the top edge at random.
• Allow Spinning To spin the particles, choose this option, and in the same event use a Spin operator. In the latter, set Rotation Axis to Particle Space and use the default axis values: X=0, Y=0 , Z=1.

Uniqueness group

The Uniqueness setting enables changing the randomization of the size/width variation.

Seed

Specifies a randomization value.

New

Calculates a new seed using a randomization formula.