Hi Matt.
Put some answers inline.
Matthew Hails wrote:
I have an existing graphics library for an embedded system, and I would
like to provide an implementation of the API using DirectFB. However,
there are two features that I haven't yet been able to work out how to
do using DirectFB:
1. Provide a double-buffered interface to a graphics layer that exposes
full draw/read/write capabilities of the visible (front) buffer as
well as the hidden (back) buffer. From my reading so far of the
DirectFB API, all drawing operations are on the hidden (back) buffer
of a double-buffered surface, and the only access to the contents of
the visible (front) buffer is read-only access via
IDirectFBSurface::Lock(). I can't see a way to, for example, blit
from an off-screen surface directly onto the visible buffer of a
surface.
Correct, this is on purpose.
Normally, if you do double buffering, you want DirectFB to do the buffer
handling itself.
It is only possible via some trickery.
two scenarios come to mind:
(1) draw to the back buffer and do a flip with the updated region. This
does a copy from back to front (potentially accelerated).
(2) if you really want to have the front buffer to be "newer" than the
back buffer, I suggest to program the flipping yourself: allocate two
single-buffer surfaces. Note that this will not allow you to swap the
surfaces if on a flip a buffer swap would be possible (via e.g. "pan" in
the fbdev driver).
2. Provide a multiple buffered graphics layer with 4 buffers. I see
that it's possible to pass the DLBM_TRIPLE flag to
IDirectFBDisplayLayer::SetConfiguration(), but I would like to use
4 buffers.
A thought for some time is to extend the surface handling to allow any
number of buffers, and to change this dynamically. Any takers? :)
Not possible yet though.
Any help much appreciated.
Regards,
Matt.
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