I do not understand why they are using DirectX11

[Ternomir]

And I think using DirectX11 may cause problems with OSX/Linux support. So i do not understand which feature of DirectX11 is needed DirectX9 has not to offer.

[Masterpintsman]

One could rephrase that as why don't they use OpenGL?

[Ternomir]

1 hour ago, Masterpintsman said:

One could rephrase that as why don't they use OpenGL?

Not exactly because there can be good reasons to use a library the programmers know. So if they have experienced DirectX9 programmers it may not be a good decision to change the library to OpenGL because if you use DirectX9 they have a higher chance to know where errors came from. And if you port it to Linux(OpenGL mostly) you may also know what to do if errors happen.

[Erasmus Crowley]

50 minutes ago, Ternomir said:

Not exactly because there can be good reasons to use a library the programmers know. So if they have experienced DirectX9 programmers it may not be a good decision to change the library to OpenGL because if you use DirectX9 they have a higher chance to know where errors came from. And if you port it to Linux(OpenGL mostly) you may also know what to do if errors happen.

ONI is built in the Unity engine, which supports OpenGL, DirectX 9 and DirectX 11.

By default, Unity chooses the "best" option for the system and build target. The priority list for Windows PCs goes DX11, then DX9, and then OpenGL. The default for Mac and Linux builds is OpenGL.

Unity developers can choose to override this behavior and force OpenGL on Windows systems if they want, but I can't think of any reason to do so.

[Ternomir]

2 hours ago, Erasmus Crowley said:

ONI is built in the Unity engine, which supports OpenGL, DirectX 9 and DirectX 11.

By default, Unity chooses the "best" option for the system and build target. The priority list for Windows PCs goes DX11, then DX9, and then OpenGL. The default for Mac and Linux builds is OpenGL.

Unity developers can choose to override this behavior and force OpenGL on Windows systems if they want, but I can't think of any reason to do so.

And why can Unity engine not choose when it is on the costumers system? Would this not make this better?

[Erasmus Crowley]

17 minutes ago, Ternomir said:

And why can Unity not choose when it is on the costumers system? Would this not make this better?

How would that make it better?

EDIT: I think I misunderstood what you were asking.

I think you might have been asking if Unity will fall back from DirectX 11 to DirectX 9 if a customer's PC can't run DirectX 11. It will do that. It will always try to use DirectX 11 first though.