Fix underwater emitter issue

[aTom3333]

While stepping into the path tracing code, i saw that a ray had its previous material set as air even though it was in water, so i added a test to set its previous material to water. I don't really understand why but it fixes the issue with underwater emitters not lighting the block around.
Fixes #528

Render with fix:

[jackjt8]

Does this resolve the issue for Test 2 where the camera is above the waters surfacing looking under? This would be a much more common scenario compared to the flawed, but more apparent Test 1. I don't believe I included the scene files for Test 2, but just raising the camera up and looking down into the water should be enough. Emittance/exposure might need to be raised a touch as it's less noticable.

1.4.6beta2

2.0beta4/5

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The only main difference I am seeing is the underside of the waters surface does not seem to be directly illuminated by the glowstone and is rather only receiving a reflection. This would be a small trade-off towards resolving this emittance issue.

[aTom3333]

Yes it does fix the issue too when the camera is above the surface
Before:

After:

The only main difference I am seeing is the underside of the waters surface does not seem to be directly illuminated by the glowstone and is rather only receiving a reflection. This would be a small trade-off towards resolving this emittance issue.

Its seems to be a separate issue that has been introduced since your tests. When rendering Test 1 without my changes i get this:

And a 16spp version where we see the pixel of the surface that have been lit up are less bright compared to the ones on your test:

[jackjt8]

Hmm.. I'll have to look through my collection of snapshots but I should be able to narrow down the changes that caused that. Otherwise this looks good.

[aTom3333]

Hmmm, i had a quick look. I went back to the commit before the separation between world octree and water octree (that caused this bug) and i can't reproduce the same king of render, even with full emitter intensity

I don't know how you got that much light on the water surface

[jackjt8]

Much confusion.

1.4.5

I'm not sure what I did either. Strange.

[jackjt8]

Right! I didn't test 1.4.5 in #528

1.4.5 does not see undersurface illumination (500SPP).

1.4.6_beta2 does (500SPP).

As with 2.0beta6 and 2.2.0-323 (only 16 SPP, so ignore the noise).

[aTom3333]

I don't have 2.2.0-323, but i have 2.2.0-322 and i still don't have the same illumination

[jackjt8]

There is no emitter noise... I would still expect some to be found on the walls. Something strange is going on and the glowstone isn't emitting any light. For you.

2.2.0-319

Can you send me a copy of those builds so I can test them my end?

[aTom3333]

Sure, here is the 2.2.0-322 build with its version file
2.2.0-322.zip

[jackjt8]

Much confusion.

[aTom3333]

I'll redownload your scene to be sure i didn't change something

[aTom3333]

Same version, same scene, different result...

[aTom3333]

Oh, found the problem x)
I was using minecraft 1.12 as texture pack. Switching to minecraft 1.15 give me the same thing you have

The water texture must be different and change how light is reflected

[jackjt8]

I would assume that's why 1.4.6beta2 has this issue and not 1.4.5. 1.4.6b2 has support for 1.13 resource packs.

[aTom3333]

So, just to confirm, the changes of this PR do not change how the water surface is illuminated