Rayportals: Disable fade-in effect for portals with to emissive texture

[xoxor4d]

This small change disables the fade-in effect on rayportals that have no emissive texture set.

The issue:

Drawing a rayportal whilst having the runtime option "Portals: Fade in Effect" enabled results in a gray, non see-through portal:
const float16_t tFactor = portalFadeInEffect ? float16_t((surface.tFactor >> 24) & 0xff) / 255.0 : float16_t(0.0);

-> There is no way to set the tFactor for the surface via the api.

Now, I could disable the global fade-in option but that will also affect the actual game portals:

And with the fix:

[anon-apple]

Yeah that seems like a good way to do it, if the D3D API isn't providing a texture then I doubt the texture factor parameter will be set or intended to do anything.

Another way would be to offer a control to enable/disable the fade in effect per-material (along with other ray portal parameters) since that might be a bit more generic for games trying to use such things more beyond just this one issue. We didn't really have much need at the time when designing the system since it was only really used for Portal RTX and could just be a global thing like that, but as you point out that's sometimes unsuitable for other uses. Would be more complex to add all those parameters through the whole material pipeline though so I think this is fine for now.

[anon-apple]

This is merged in now in 912a614. Closing this now.