On Sun, 9 Jun 2002, Paul wrote:
> Hi,
>
> Just having some trouble getting my SDL application to get double-buffering
> going using a Trident cyberblade/i1 chipset (embedded in a VIA VT8601
> Northbridge) xdpyinfo reports double buffering and dga are present and
> xvinfo reports back ok (4 image formats including YUV). I am using the 4.2.0
> package compiled from source.
>
> I don't get retrace synced flips so I get tearing and "really fast scrolling
> ;) (should be limited to refresh rate) ". Video playback tears very badly
> as well. My app uses SDL-1.2.3 and runs using DGA as root.
>
The double-buffer extension, DGA and Xv are all independent extensions
and don't have anything to do with each other.
The double-buffer extension does not sync to the refresh on
XFree86. It uses the code in the X.org sample implementation which
transparently implements this extension by using Pixmaps for the
back buffers and plain old XCopyArea to swap the buffers. I'm
not sure that there are even hooks for a driver to implement
synchronized buffer swapping if the hardware was capable of
it.
DGA can page flip synced to the refresh provided you use it correctly
and the driver isn't broken. My experience has been that many DGA
drivers are broken.
Ideally Xv won't tear but that's up to the driver. Some drivers tear
because synchronization with the refresh can't easily be done from
a user-space driver. Some hardware is interrupt driven and needs
kernel support in order to do that correctly.
Mark.
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