We are mainly in the business of building kiosk type application involving multiple screens. Because of that we often have machines running multiple video cards each driving several screens.
In order to make that work with Unity3D we’ve been using SoftTH (kegetys.fi - SoftTH Software Triplehead). This allows us to use Unity in fullscreen mode spanning one Unity app across all monitors. SoftTH works by rendering the whole scene on one display adapter, which then gets split into different parts to be displayed on each monitor.
All we need to do is add the SoftTH d3d9.dll into the application folder and select the full resolution in the Unity Startup dialog window. Without SoftTH this resolution is not available in the listbox.
In the new Unity 4.6 release however this approach no longer works. The fullscreen mode is now limited to 1 logical screen. The new setting in the dialog screen which allows you to select a monitor in fullscreen mode most likely has something to do with that.
The only way now to achieve the same result is by using the -popupWindow startup option, in combination with SoftTH(when using multiple videocards) and not using true fullscreen mode (checking the ‘Windowed’ checkbox) The big downside however is that there is an enormous performance hit involved when using this approach. We’ve noticed performance dropping from 60FPS down to 20FPS or less.
For now it seems like we won’t be able to use 4.6 or above, unless we can somehow bypass this new monitor feature.
Because of the very specific nature of this issue we are afraid it will not be picked up as a bug during testing, since it’s only going to be a problem in situations where multiple videocards each driving multiple screens are used.