IDirectDrawSurface7::PageLock method (ddraw.h)
Prevents a system-memory surface from being paged out while a bit block transfer (bitblt) operation that uses direct memory access (DMA) transfers to or from system memory is in progress.
HRESULT PageLock( [in] DWORD unnamedParam1 );
Currently not used and must be set to 0.
If the method succeeds, the return value is DD_OK.
If it fails, the method can return one of the following error values:
You must call PageLock to make use of DMA support. If you do not, the bitblt occurs by using software emulation.
The performance of the operating system can be negatively affected if too much memory is locked.
A lock count is maintained for each surface and is incremented each time that PageLock is called for that surface. The count is decremented when IDirectDrawSurface7::PageUnlock is called. When the count reaches 0, the memory is unlocked, and can then be paged by the operating system.
PageLock works only on system-memory surfaces; it does not page-lock a display-memory surface or an emulated primary surface. If an application calls PageLock on a display memory surface, the method does nothing except return DD_OK.
IDirectDrawSurface7::PageLock was not implemented in the IDirectDraw interface version.