[2/8] wined3d: Select the right shader backend when creating the device

[Ivan Gyurdiev]

> - Software shaders currently simply don't work. If we do get software
> shaders it'll likely be vertex only.
So, we should allow hardware pixel shaders, and software vertex shaders.
>  I could see
> someone using software vertex shaders if he's got no hardware support
> for shaders, although it's questionable if such a card would be able
> to effectively run an application that requires them anyway. 
Software shaders are chosen if (1) there's no support for hardware, (2) 
the user elected software, or (3) the application elected software, and 
(3) is required as part of the DirectX spec.
> Mesa is
> possibly a better option there. Either way, you're not going to be
> using software vertex shaders together with HW pixel shaders, that's
> just silly
Well, I was able to identify at least one bug that way [ improper 
initialization of vertex shader output register ].
> So imo it just adds complexity to the code without giving much of a 
> benefit.
You're taking two logically separate concepts, and merging them together 
for no good reason at all. I'm just not sure what the purpose is - at 
the very least you'd be able to turn off pixel and vertex separately as 
a user override. Once geometry shaders come into play, I think they 
should get their own flag too.