ScreenUnlock

Unlocks work page's framebuffer

Syntax
   Declare Sub ScreenUnlock ( ByVal startline As Long = -1, ByVal endline As
   Long = -1 )

Usage
   ScreenUnlock [ start_line ] [, end_line ]

Parameters
   startline
      optional argument specifying first screen line to be updated. If 
      omitted, top screen line is assumed.
   endline
      optional argument specifying last screen line to be updated. If 
      omitted, bottom screen line is assumed.

Description
   ScreenUnlock unlocks the current work page assuming it was previously 
   locked by calling ScreenLock and lets the system restart updating the 
   screen regularly. When called with start_line and end_line , only the 
   screen area between those lines is assumed to have changed, and will be 
   updated. 

   An internal counter exists that remembers the screen lock state, thus 
   ScreenUnlock has an effect only on a screen that is locked.  A screen 
   that has not been locked with ScreenLock cannot get unlocked, however 
   ScreenUnlock still will force an update of given area or full screen.   

   Calls to ScreenUnlock must be paired with matching calls to ScreenLock.  
   Only the first call to ScreenLock actually performs a locking operation. 
   Subsequent calls to ScreenLock only increment the lock counter.  
   Conversely, ScreenUnlock only decrements the lock counter until it 
   reaches zero at which time the actual unlock operation will be 
   performed.  Using Screen or ScreenRes will release all locks and set the 
   lock counter back to zero before changing screen modes.

   All graphic statements automatically lock the screen before the function 
   call, and unlock the screen afterwards, so you do not need to do this 
   explicitly using ScreenLock and ScreenUnlock. You only need to lock the 
   screen when you wish to access the screen (framebuffer) directly using 
   ScreenPtr  or when you wish to group several graphic statements together 
   so their effects appear simultaneously on screen, thus avoiding 
   potential screen flicker during screen updates.

   Warning (Win32, Linux) : The screen is locked by stopping the thread 
   that processes also the OS' events. This means the screen should be 
   locked only for the short time required to redraw it, and no user input 
   will be received while the screen is locked. When the induced lock time 
   becomes too long, use preferably the method of double buffering (with 
   ScreenCopy).

Example
   See ScreenPtr example.

Dialect Differences
   * Not available in the -lang qb dialect unless referenced with the 
     alias __Screenunlock.

Differences from QB
   * New to FreeBASIC

See also
   * Screen (Graphics)
   * ScreenLock
   * ScreenPtr

