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IVfxShape

14.1 Interface

Inheritance 6 descendants

Class Documentation

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A spawn shape: the object in the SpawnShape of an emitter that places each new particle relative to the birth position. A shape returns an offset in the emitter's local frame and can turn the particle's birth velocity and birth acceleration.

When a shape is sampled

Complex and simple emitters both apply the shape, once for every particle at birth. For each particle the emitter:

  1. Computes the birth velocity and birth acceleration.
  2. Takes the offset from the shape.
  3. Applies offsetLifetimeScaling to the particle's lifetime with this raw offset.
  4. Multiplies the offset by the offset factors of FlexShapeDefinition and by the system scale.
  5. Adds the emission mesh or emission surface point to the base position. When useEmissionMeshNormalForBirth is set, it points the velocity and acceleration along the surface normal.
  6. Lets the shape turn the offset, the velocity and the acceleration by one rotation.
  7. Sets the birth position to the base position plus the offset.

A VfxShapeLegacy also evaluates its curves once per spawn step, before the particles of the step are made. The other shapes have no curves.

Rotation of velocity and acceleration

The shape returns no normal. Its only effect on motion is the rotation in step 6: the rotation that places the offset also turns the birth velocity and birth acceleration. A velocity authored along the direction in which the shape seeds its offset therefore leaves the shape outward.

Shape Rotation Effect on the birth velocity
VfxShapeSphere Random turns about Y, then Z A velocity along +X points away from the centre.
VfxShapeCylinder A random turn about Y A velocity along +X points away from the Y axis.
VfxShapeBox Random quarter turns, or none in interior mode A velocity along +Z becomes the normal of the chosen face. In interior mode the velocity is unchanged.
VfxShapeLegacy The authored turns The velocity turns with the offset.
VfxShapePointDoNotUse None The velocity is unchanged.

The shape does not set the particle's orientation. A direction-oriented particle (isDirectionOriented) follows the turn only through its velocity.

Referenced by 2 classes · 2 properties