Difference between revisions of "State"

From Second Life Wiki
Jump to: navigation, search
(I hope this wording is more obvious.)
(Added "global functions cannot change state" caveat)
Line 80: Line 80:
 
*The ''default'' state must be defined before all others.
 
*The ''default'' state must be defined before all others.
 
*States cannot have user functions or variables inside their immediate scope, only event definitions may be inside a states scope.
 
*States cannot have user functions or variables inside their immediate scope, only event definitions may be inside a states scope.
 +
*States cannot be changed inside of user-defined (global) functions. The compiler will throw the error 'ERROR: Global functions can't change state'.
 
}}
 
}}
  

Revision as of 09:25, 6 June 2010

In LSL, most scripts sit idle until they receive some input, or detect some change in their environment. At any moment, the script is in some state, and will react to events or inputs according to some scheme defined by the programmer. However, a script can also contain two or more different states, and react differently to events or inputs depending on what state it is in.

The main state is the default state. When a script is compiled, reset or loaded, this is the state it enters by default. After the default state definition can follow additional state definitions which the script may use to change how and which events are handled.

The correct title of this article is state. The initial letter is shown capitalized due to technical restrictions.

default { events }

default { events }
• event events one or more events

The default state definition.

state target { events }

• label target state name
• event events one or more events

target state definition.

state target;

• label target name of a state to run

When a state target; is encountered at runtime, if the current state and the target state are different:

  1. Trigger state_exit in the current state if it exists and clear the event queue.
  2. Change state to target, any listens are unregistered.
  3. Trigger state_entry in the target state if it exists.

If target state is the same as the current state, no state change occurs nor do any of the side effects.

Caveats

  • On state change:
    • All listens are released.
    • The event queue is cleared. (see Notes for a partial workaround)
    • Repeating sensors are released.
    • The timer event clock is not cleared.
    • This means if the new state has a timer event, and the previous state has a timer set, the timer event in the new state will be triggered on the interval set in the previous state.
  • The default state must be defined before all others.
  • States cannot have user functions or variables inside their immediate scope, only event definitions may be inside a states scope.
  • States cannot be changed inside of user-defined (global) functions. The compiler will throw the error 'ERROR: Global functions can't change state'.

Important Issues

   Server drops first touch event when a script returns to a state with a touch_start handler

Examples

<lsl>default {

   touch_end(integer a)
   {
       state hello;
   }

}

state hello {

   state_entry()
   {
       llOwnerSay("Hello");
       state default;
   }
   state_exit()
   {
       llOwnerSay("Goodbye");
   }

}</lsl>

Notes

  • To avoid dumping previously queued events, consider moving the state target command to the timer event, and calling it with llSetTimerEvent( 0.01 ), then stopping the timer in state_entry of the new state. Do NOT use state_exit if this is a concern.

See Also

Keywords

•  jump
•  return

Events

•  state_entry
•  state_exit

Deep Notes

Issues

   Server drops first touch event when a script returns to a state with a touch_start handler