Unlocks work page's framebuffer
ScreenUnlock [ start_line ] [, end_line ]
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.
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
, 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
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
. 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
- Not available in the -lang qb dialect unless referenced with the alias __Screenunlock.
Differences from QB