VisibilitySensor

Definition :
VisibilitySensor {
  exposedField SFVec3f center   0 0 0
  exposedField SFBool  enabled TRUE
  exposedField SFVec3f size     0 0 0
  eventOut     SFTime  enterTime
  eventOut     SFTime  exitTime
  eventOut     SFBool  isActive
}
Explanation :

The VisibilitySensor detects visibility changes of a rectangular box as the user navigates the world. VisibilitySensor is typically used to detect when the user can see a specific object or region in the scene, and to activate or deactivate some behavior or animation in order to attract the user or improve performance.

Each VisibilitySensor behaves independently of all other VisibilitySensors - every enabled VisibilitySensor that is affected by the user's movement receives and sends events, possibly resulting in multiple VisibilitySensors receiving and sending events simultaneously. Unlike TouchSensors, there is no notion of a Visibility Sensor lower in the scene graph "grabbing" events. Instanced (DEF/USE) VisibilitySensors use the union of all the boxes defined by their instances to check for enter and exit - an instanced VisibilitySensor will detect enter, motion, and exit for all instances of the box and send output events appropriately.

center :
enabled :
size :
enterTime :
exitTime :
isActive :