[visionegg] Motion tearing on PC

Hi All,

I have a motion stimulus that is made up of dots
that I've tested on a Mac and a PC and it runs fine
on both systems except on the PC it tears. It is synced
with the VBL(both thru Visionegg and the ATI control panel)
and I get back the correct frame rate
so it looks like the PC is blitting from the back to front
buffer during a swap buffers whereas the MAC is
page-flipping. The card in the PC is a AGP Radeon 7000.
Not the fastest of cards but they work fine on the MAC.
I experienced this before on MACS when OS9 came out
and you could allocate GWorlds in VRAM a CopyBits
would always tears in VRAM but not in normal ram.
It's consistent with blitting from the bottom up cause the
bottom portion of the stimulus is ahead of the top portion and
the higher your resolution the further down the screen the tear
appears. I know the Mac page flips
but I don't know about Windows or whether this is in the ATI
driver or the Windows side. If it's on the Windows side it should
appear on all cards unless the blit speed is so fast that a whole
frame can be blitted during the VBL. Has anyone else seen this?
Thanks much,

Doug Taylor


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