Direct Framebuffer Access
In order to allow both direct framebuffer access and hardware accelerator
access, contention for video memory between the application program and
the hardware accelerator must be properly handled. This is
provided by the EnableDirectAccess and
DisableDirectAccess functions.
If the EnableDirectAccess function
pointer is not NULL, then you must call these functions prior to
performing any direct access to the framebuffer via either the banked
framebuffer or the linear framebuffer, and then call DisableDirectAccess before
calling any other hardware accelerator functions again.
If the EnableDirectAccess function
is NULL, you must instead call the WaitTillIdle function
to ensure the hardware has completed the last drawing operation before
accessing the framebuffer directly. You need not call any other
functions to return to accelerated rendering again.
When the video mode is first initialized, the hardware is automatically
set up for hardware accelerated rendering, as though DisableDirectAccess was
called immediately after setting the display mode.
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