Tilo -
Here is what we (Red Mercury) know about WinScreenUnlock:
If WinScreenUnlock is not supported, it will return NULL.
Devices known to do this:
Non-color Sony Clie
Handspring Visor Prism
If WinScreenUnlock returns NULL, that means it did not switch the screen, so
subsequently calling WinScreenUnlock will throw the "unlock out of sync" as
you have found.
Various Palm OS licencees will continue to have reasons not to support
WinScreenLock. For example, at a particular bit depth with a particular
video controller, there may not be enough video RAM to double buffer. If the
frame buffers are in core memory, there might not be enough RAM for the OS
to allocate a second frame buffer. And if a licensee is having any problems
implementing or testing WinScreenLock, it is legal for them to just return
NULL according to the documentation. In other words you can't depend on it
right now.
While OS 5.0 is still in development, this is a great time to let the Palm
OS engineers know what type of video support functions you would like to
see, and what you would like to be able to depend on. Personally, I'd like
to see reliable double buffering and page flipping support in the OS, as
screen tearing is already visible on the IIIc and Prism screens. When we get
an ARM system with a quarter-VGA active matrix screen, blitting an
off-screen buffer directly to the active display won't cut it.
I've written a small demo app called Bufferoo to show screen tearing
artifacts on the IIIc. It allows you to switch between page-flipping and
WinDrawBitmap-to-active-display modes. I've emailed it to Palm, and it's
available here:
ftp://red-mercury.com/bufferoo.zip
The readme includes a long winded pathetic argument for double buffering and
page flipping.
>From what I can tell, the Palm engineers don't need a long winded
explanation of why page flipping is good, they just need to know that enough
people want it to make it worthwhile for them to support it, and worthwhile
to require (or strongly encourage) licencees to build hardware that will
support it. So if anyone else out there thinks it's important, now would be
the time to discuss it.
Scott
http://www.red-mercury.com
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