How Lock/Bond Works

Lock/Bond has three main functions:

• Attaching particles firmly to an object, either at the start of an animation or as a result of a collision
• Moving particles along or near an object's surface with a flexible attachment
• Ejecting particles from an animated object

In setting up these effects, you will find that the four most important parameters are Lock To Surface, Snap To Surface, Restrict To Surface, and Force. Different settings for these parameters, along with a few other parameters and operators, can create a variety of effects with Lock/Bond.

Attaching Particles to an Object

When particles enter an event containing a Lock/Bond test with the Snap To Surface option enabled, each particle is locked to a specific point on the selected object's surface. This point is referred to as the particle's lock point. If the object is animated, the lock points animate along with the object.

With Lock/Bond, particle attachment is controlled largely by the Force % parameter in the Position Lock/Bond group. In general, when Force %=100.0, particles stay firmly stuck to their lock points, even on an animated object. For firm attachment, the Lock/Bond test should be the last action in the event. If there are other operators below Lock/Bond that modify speed, then the overall attachment might not be as firm as desired.

All parameters in the Lock/Bond test are animatable. Therefore, you can animate Force % to lock down particles gradually or loosen them from their locked positions.

Position Object vs. Lock/Bond

The standard Position Object operator can generate particles randomly on the surface of an object. Position Object is useful for some types of animation, but is limited in its functionality. The Lock/Bond test overcomes many of these limitations, as described in the following points:

• When an object to which particles are attached is rotated, the Position Object operator does not rotate the particles along with it. The effects of this limitation are not necessarily visible with tiny or round particles, but it becomes obvious when using directional-type particle instances such as arrows or darts. Lock/Bond rotates the particles along with the object to which they are locked.
• When particles are passed to a new event that has a Position Object operator and the particles are meant to land on the object's surface, particles do not necessarily lock to the exact spot on which they land. This is because Position Object generates particles randomly on the surface, and they are not "glued down" to a specific spot on a specific face or vertex. Lock/Bond attaches each particle to a specific location on the object's surface so particles don't drift in relation to the surface.

The Position Object operator can be useful in conjunction with the Lock/Bond test. For example, you can use Position Object to cover an object with particles before locking them down with Lock/Bond, as described in the following section.

Covering an Object in Particles

To cover an object in particles, add a Position Object operator to the same event as the Lock/Bond test. The Position Object operator places particles randomly on the surface, while the Lock/Bond test locks or animates them with Lock/Bond forces and parameters.

To cover the object with particles, make sure the Amount setting in the Birth operator is high enough to create the necessary quantity of particles. The Birth Texture operator generates complete, even coverage when using Face subdivision.

After the object is covered in particles, you can lock them to the surface as the object animates, make them drift over the surface, or fling them off the object.

Locking Particles to an Animated Surface

An animated surface is one that deforms, or changes shape, over time. Examples of animated surfaces are objects with:

• Parameter animation
• Sub-object animation (animated vertices or faces)
• Morphed objects
• Surfaces animated with skinning modifiers such as Skin and Physique

Transform animation (position, rotation, scale) at the object level is not considered an animated surface.

Use these parameters to lock particles to an animated surface:

When Force %=100.0, particles stay firmly stuck to their lock points. The exception is when Speed Limit is on and the object is animated. In that case, particles stick to their lock points only if they can keep up with them without exceeding the specified velocity (Speed Limit). If this parameter is off, there is no distance or speed limit, and particles stay firmly stuck to their lock points.

A Force % value of 100.0, coupled with Offset Limit and Speed Limit off, forces the particles to stay on the surface.

Moving Particles Along or Near an Object's Surface

To allow particles to move along an object's surface, Restrict To Surface must be on and the Force % parameter in the Position Lock/Bond group must be set to a value lower than 100.0.

Any Speed or Force operators in the event will then act on the particles to move them along the surface. These forces are applied in such a way that they cause the particles to oscillate with and against the force, gradually slowing down (dampening). You can control the amount of dampening in the particles' motion with the Dampening parameters in the Position Lock/Bond group.

When Restrict To Surface is on, all Force and Speed operators should be above the Lock/Bond test, while Collision and Spawn tests should be below the Lock/Bond test.

Moving Particles Along a Surface

If you want particles to drift along the surface of an object, use the following settings:

Add Speed and Force operators to the event to make the particles move in a particular direction. For example, you can use a Wind space warp with a Force operator to push all the particles onto one end of the object.

Drifting Particles

Lock/Bond can also cause particles to drift slightly but always stay a short distance from their lock points. The area around each particle's lock point is called the central zone. Each particle has its own central zone, which extends to a specified radius around the lock point.

In the No Force In Central Zone group, turn on For Acceleration or For Dampening, and set Radius to the distance around each lock point in which the particle can freely move. The Radius setting determines the central zone.

Ejecting Particles from an Animated Object

Lock/Bond can also cause particles to be ejected, released, or flung from an object's surface when they achieve a specific speed or acceleration.