Reactors

To give an animation a higher level of sophistication, it requires the use of reactors. A reactor is a tool that makes an object react to something. For example, if the rigid body collection which is one type of reactor is applied to a sphere and a mass element is applied to it as well. It means that it fall to a surface. If there was a board beneath that was on a tilt, then the sphere would roll off of the board as well.

Whereas, if the cloth modifier was to be added to a plane, and then the cloth collection was then applied. It is possible to make a curtain effect by attaching vertices to their hooks which could be a sphere of cylinder. By using Auto Key, a short animation can be created and make the curtains slide from one end to the other as if they were being opened.

A quick guide is below on how to create the curtain effect:

1. Make the plane, name it curtain. Make your hooks out of cylinders or spheres and place them on a long cylinder that will act as the pole.
2. Select the plane (curtain) and select the cloth modifier which is in the reactor tool bar, (if this is not visible select reactor from the create panel and then right click on the main tool bar and select reactor, it should now appear. Note: if the cloth collection is applied before the modifier it will not work. The cloth modifier should now appear in the stack.
3. For the curtain pole, attach a rigid body - ensure that the curtain (plane) is not placed in this (remove if so).
4. Now go to the cloth modifier and select vertex at sub-object level, followed by constraints and click to attach to rigid body.
5. Change the name that appears in the dialog box as it will get very confusing later, and then highlight the vertices around the hook. Select none, then click on the hook. It should then turn yellow on those vertices selected to show it is complete. Complete this step for each of the hooks.
6. Select preview animation, press 'P' and the cloth should be moving. The animation can now take place by moving the hooks to make the curtains open.