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Multiple Monitors?

Started by NotTaxes Jun 20, 2002 at 3:30 AM 2 replies 250+ views

Original Post

Jun 20, 2002 at 3:30 AM

Hi, I''m using two monitors with a Geforce2 on the one and a Voodoo5 on the other. If I run my DirectX app on the one monitor in windowed mode and then drag it to the other monitor, the frame rate drops significantly, but it still displays. Now, I figure that with DirectX, all of your directx objects are bound to the display driver that you start off with, which in this case would be the GeForce2. But then... the second monitor is being handled by the Voodoo5, and yet the app still runs on that monitor... Is this just something pretty cool that Windows is doing in the background (like keeping the directx app on the geforce, shunting the output to a bitmap and rendering it on the voodoo5 without changing the directx info)? I was hoping I could drag & drop the app between the two monitors and get an idea of the difference in quality and performance, but it doesn''t quite work like that. If I switch the default driver to the voodoo and re-run the app, the app starts on the Voodoo monitor at about the same frame rate, and then drops again if I move it to the geforce monitor. This implies that windows is doing something funky on its own without really messing with DirectX at all. Anyway, I''m just curious.

CamelFly

Jun 20, 2002 at 3:49 AM

I also have a multimon system and windows does exactly the same thing for me. My conclusion is also that it is Windows that does something funky rather than DX.

Dean Harding

Jun 20, 2002 at 3:54 AM

When you''re in windowed mode, all that happens when you call Present is that the image is copied from the back buffer to the front buffer - it''s not "flipped" or anything.

So, when you copy from the back buffer to the front buffer on your GeForce monitor, it''s fast because it can all stay in video memory. When you copy from the back buffer to the front buffer of your voodoo, it''s slow because it has to go from video memory in the GeForce to system memory, then from system memory to video memory of the voodoo.

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Coward

Jun 20, 2002 at 4:08 AM

Multimonitor support in windows works like ass anyway...
On this box I''ve got two gfx cards, one supporting gl (Geforce 256) and one who doesn''t (S3 Virge)....
Running GLQuake, while both monitors are enabled, makes it go VERY slow (from 600 fps to >10 fps), when only on geforce, when only on s3 virge and when splitting it between...
But notice that it does run on the S3 virge....
So I''d think you''re right... Windows render the scene on the geforce just copy the final result to whatever card might want to show it...

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