Unlocks work page's framebuffer

declare sub Screenunlock ( byval startline as long = -1, byval endline as long = -1 )

Screenunlock [ start_line ] [, end_line ]

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

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).

See Screenptr example.

Dialect Differences:
Differences from QB:
See also:
Back to Screen Functions
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