Action Object

Action objects represent independent processes which are carried out on particles or other X-Particles objects when the conditions in a Question object are satisfied or when they are triggered in some other way (such as a collision, for example). They have no on-screen presence, either in the editor or at render time.

You can add an Action object to the scene in several ways:

  • by selecting a System object and in that object selecting an Action from the drop-down menus in the 'Actions' section; this will add an Action object to the scene, but will not link it to any Question object
  • by doing the same thing from the 'Actions' folder which is a child of the System object;
  • by clicking the 'Add Action' button in a Question object; this will add an Action object to the scene and will automatically link it to that Question object
  • by selecting the 'Action' menu entry from the 'Other Objects' sub-menu of the X-Particles menu in Cinema 4D; this will add an Action object to the scene but you will have to link it to a Question or other object yourself if required
  • by clicking an 'Add Action' button which is present in several modifiers and other objects

Important: Action objects have no effect on any particles until they are added to the Actions list of a Question object (or in some cases a modifier or other object). Note that more than one Question can make use of the same Action if desired simply by dragging the Action into each Question object you want to carry out this Action.

When you have an Action object you can set various parameters in it. One action - the 'Editor Display Only' action - is always available, even if you select another action type. With this, you can alter the particle display in the editor, which can be helpful to see which particles are being affected by the Action and when they are affected (you can see when an Action occurs by changing the particle colour, for example).

You can change the Action at any time by first choosing the general type of Action from the 'Action Type' menu and then choosing the desired Action from the secondary menu below the 'Action Type' menu.

Note that you can turn off an Action at any time by disabling it in the Object Manager (so the green tick turns to a red cross), or by disabling any Question objects or modifiers which use the Action.

It is most strongly recommended that you rename the Action objects you create to reflect what they do. In a complex setup you might have numerous Actions, and picking the correct one to change its parameters can be difficult. To help you a little, the icon in the Object Manager against each Action object will change depending on the type of Action selected, but a meaningful name is even more helpful.

Actions and Groups

Actions have their own group list and will only affect particles in those groups. But what if a modifier also has a groups list with groups in it? What will be the result of affecting the same or different groups in the action and the modifier?

Suppose you have a scene with two groups, an action, and a modifier which is turned on by the action. The various possible results are shown in the table:

Action Groups Modifier Groups Result
No groups in the list No groups in the list All particles are affected by the modifier
Group 1 in the list No group in the list Only particles in group 1 are affected by the action or by the modifier if it is activated by the action
Group 1 in the list Group 1 in the list Only particles in group 1 are affected by the action or the modifier
Group 1 in the list Group 2 in the list No particles at all are affected by the modifier (because although the action activates the particles in group 1 to be affected by the modifier, the modifier itself will only affect group 2 particles - which have not been activated)
All groups in the list Group 2 in the list Only particles in group 2 are affected by the modifier (because the modifier will only affect group 2 particles)

To avoid confusion we recommend that if controlling modifiers with actions, and you want to use groups to select which particles are affected, you put the groups into either the modifier or the action, but not both.

How Actions work

Many, but not all, Actions work by activating or deactivating a particle modifier so that the modifier does, or does not, affect a particle, rather than acting directly on the particles themselves. For example, a 'Change Gravity Modifier' action will alter a linked Gravity modifier by altering its effect on a particle so that the modifier either affects a particle or does not. Actions which only turn a modifier on or off for a particle are found in the 'Control Modifier Actions' menu.

Other Actions work by directly changing a particle's parameters in some way, such as the 'Unstick from Source Object' action. There are only a few Actions which only affect a particle's parameters and these are found in the 'Other Actions' menu.

Some Actions can do both - a direct change when convenient or control a modifier if desired. These are found in the 'Direct Actions' menu.

Finally, some Actions work on another XP object rather than a particle. These are found in the 'Object Actions' menu.

Remember that all Actions which work through a modifier do so on a per-particle basis - that is, they influence individual particles rather than all particles at once.

Controlling a modifier

If you want to control a modifier with an Action, you must first set the modifier to 'Action-Controlled'. If it is set to 'Independent' the action will have no effect on it and the modifier will work as a standalone modifier.

It is important to understand how Actions affect modifiers. As already stated, an Action-Controlled modifier will not work on all particles from an emitter, but just those which have been flagged by the Action to be acted on by the modifier. The Action does this by altering the particle, in effect making it susceptible to that specific modifier.

You can specify that a modifier only works on certain particles, though. You can ignore a modifier for all particles from a particular emitter by dragging the modifier to be ignored into the emitter's modifier exclusion list. Or, you can arrange it so that the falloff of a modifier only affects the particles you want it to.

Available Action types

X-Particles 4 ships with 59 different Actions. These actions are grouped into five types as follows:

  • An action to change the editor display (which is also available in the interface of all other actions).
  • Object Actions: these actions affect X-Particles objects to change the object settings. They may also change certain particle data (e.g. the Change Trails action).
  • Control Modifier Actions: these actions only control a modifier, usually only to the extent of activating or deactivating it for a particular particle.
  • Direct Actions: these actions have a dual role. They can change particle data directly, such as the speed or radius. But they can also control an associated modifier in the same way as the Control Modifier actions.
  • Other Actions: a group of miscellaneous actions that don't seem to fit anywhere else!

The currently available Actions are as follows: