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I was wondering.. if I connect one monitor to the discrete GPU and another to the integrated, how is it determined which GPU renders which parts?

For example, if I open a game on the monitor connected on the discrete, I guess it'll be rendered the discrete, but what happens if I put the game in windowed mode and move it in between both monitors?

Will each GPU render half of the game? If so, what happens with the difference in rendering speed?

Will it still be rendered by the discrete? If so, how does the information get to the other monitor?

  • Are you talking a laptop with a dual GPU, or a desktop machine with graphics on the motherboard and a separate graphics card? The laptop answer is below already, the desktop answer wouldn't be consistent since it depends on the application, conditions, etc, – acejavelin Mar 22 '17 at 11:24
  • Im talking about a desktop machine with graphics on the motherboard and a separate graphics card. Ok, so if it depends on the application, let's assume its a game and that the discrete GPU renders it. If I put the game on the monitor connected to the iGPU, how does the rendered pixels go from the discrete graphics card out through the motherboard into this second monitor? – ladorm Mar 22 '17 at 11:35
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    That is a function of the operating system... In Windowed mode, applications use the OS's functionality and graphics calls (like DX), they do not talk directly to the GPU (notice how when you window a good full screen game, the graphics quality dips noticeably?), so the most likely case is the app will slow down significantly, or crash. Try it, it won't hurt anything. It would be better to connect two+ monitors to the same GPU though unless you are doing something like dedicating a GPU to a VM. – acejavelin Mar 22 '17 at 12:35
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Pluging an external monitor doesnt change which gpu runs what application. It's the drivers that controls that. I'm assuming that you have a laptop (since usually, desktops disable iGPU if you plug in external gpus) then it is the switchable graphics system that activates the dGPU if configured to do so, else the integrated gpu will do the job. Switchable graphics do not allow 50/50 rendering by iGPU and dGPU. This would be complicated anyway since both do not run/process at the same speed. Usually dGPU is way faster than iGPU but also more power hungry.

Optimus

For instance Nvidia's Switchable graphics technology has an interface in the control panel that can configure that (see linked screenshot). Optimus Choice

  • I was actually talking about a desktop machine, but this is good to know as well! I replied to a comment on my question explaining some more – ladorm Mar 22 '17 at 11:41

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