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JoeZ

DirectDraw and Duel Monitor

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HI: I am writing a game for a dual monitor system. I''d like to know how to use GetVerticalBlankStatus and GetScanLine to get infomation from both monitors so I can synchronize the flip. So far I can only get the vertical blank status and get the scan line from the primary monitor. Thanks.

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Are you using a dual output card (e.g. DualHead, TwinView etc) or two separate cards (e.g. an AGP and a PCI) ?

If its separate cards, which are they ? - some cards simply don''t support functions like GetScanLine (or at least they don''t expose it via their drivers). This is particularly true of some older PCI cards.

Actually I''m not sure you can reliably sync two monitors to the same vsync at all under any consumer level PC API anyway!

Also, if you are using cards in different slots - consider throughput differences - they can occur.

IMO a much more robust way to do it would be to totally unlink the monitors from the actual game, so that they both just take snapshots of the game state *in their own time* so MonitorA might be synced at 60Hz and MonitorB at 85Hz, but the game runs at a constant 100Hz.

A slightly simpler alternative if your whole game loop is timed off the vsync and changing would be a pain is to sync the game off MonitorA, then let the code driving MonitorB snapshot the state

--
Simon O''Connor
Creative Asylum Ltd
www.creative-asylum.com

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Thanks for your reply Simon.

I am using a Radeon 7500 dual head output video card.

I am thinking that if I can get the vertical scan status from both monitors I can just reset the resolution of one of the monitors (everytime the resolution is reset the vertical scan restarts). Maybe after 10 to 20 times of reset the monitors will be synchronized. : )

JoeZ
3D Research Center

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