call-as-current in gl-context<%>

Calls a thunk with this OpenGL context as the current context for OpenGL commands.

The method blocks to obtain a lock that protects the global OpenGL context, and it releases the lock when the thunk returns or escapes. The lock is re-entrant, so a nested use of the method in the same thread with the same OpenGL context does not obtain or release the lock.

The lock prevents interference among OpenGL-using threads. If a thread is terminated while holding the context lock, the lock is released. Continuation jumps into the thunk do not grab the lock or set the OpenGL context. See gl-context<%> for more information on interference.

The method accepts an alternate waitable for use while blocking for the context lock; see sync, section 7.7 in PLT MzScheme: Language Manual for more information on waitables.

The result of the method call is the result of the thunk if it is called, or the result of the alternate waitable if it is chosen instead of the context lock.

If ok? returns #f at the time that this method is called, then an exn:fail:contract exception is raised.

• (send a-gl-context call-as-current thunk alternate enable-breaks?) -> return value of thunk or waitable
   thunk : a procedure of no arguments
     alternate = permanently blocked waitable : waitable
     enable-breaks? = #f : boolean

  If enable-breaks? is true, then the method uses sync/enable-break, section 7.7 in PLT MzScheme: Language Manual while blocking for the context-setting lock instead of sync.