Implement GraphicsAdapter.QueryRenderTargetFormat()

[nkast]

Fallback of unsuported and profile depended SurfaceFormat. (Dxt, Single, drBlendable, ...)

Not implemeneted:
Optional/Device depended formats. (566, 4444, ...)
Depth Formats.
MultiSampleCount.

[dellis1972]

This works on GL based systems too right?

[nkast]

Yes, this works on all platforms in a way compatible with XNA. So far I doesn't depend on the device.
The changes in GraphicsAdapter.Legacy.cs and GraphicsAdapter.cs are identical.

After it's merged we can use it to fix #6036 and also pass the tests of b26f927.

[nkast]

If we are going to use this QueryRenderTargetFormat() in the RenderTarget/Texture construction it will change the behavior depending on the Profile. For example, HdrBlendable will become Color under Reach profile. I think I should move some of this code in #5451.

The way this is going work on the Texture construction:

bool isSupported = device.adapter.QueryRenderTargetFormat(device.Profile, prefferedSurfaceFormat, out surfaceFormat);
if(!isSupported)
{
if(this is IRenderTarget)
 surfaceFormat = prefferedSurfaceFormat;
else
 throw new Exception(device.Profile + "does not support surface "+ prefferedSurfaceFormat);
}

That won't be a good error message because some formats (DXT, NormalizedByte2) are not supported as RenderTargets in any profile.
So I think I will post a fix for #6036 that does not really on QueryRenderTargetFormat() but does some checks inline and throws a better error.

[nkast]

Ok, I have a new PR #6170 that fixes #6036 without the Profile fallback.

[nkast]

#6170 is merged. I moved the rest to #5451