Alpha materials not visible through water surface about crest HOT 6 CLOSED

Yes this is a common problem with refract surfaces like water. I brainstormed some "solutions" below, but i dont think any of them are perfect..

Solution A: Render your transparents as opaque..!? Sounds dumb but maybe with it can be faked to look transparent or something!

Solution B: Render using alpha test - if this helps at all?

Solution C: If you're using TAA, you might be able to go full stochastic transparency - render as alpha test and randomly accept or reject pixels using a noise function and the desired alpha as the probability. I'd be surprised if this can work really well but its possible i guess..

Solution D: Refuse to accept that alpha does not work and strong arm it into submission:

1. Render your alpha towards the end of the opaque pass (!) - perhaps queue 2450 or something (so Geometry+450). EDIT: as i've just discovered the hard way, Renderer.sortingOrder takes priority over the queue setting it seems, so additionally you'll need to see the sortingOrder to less than say -16, to render before any ocean lods.
2. When it blends onto the background it will need to fake depth fog between itself and the opaque surface behind. So if it is 5m above the sea floor, it should compute scattering using the same technique as the ocean shader, using the same density values. This will give an alpha value and colour which it should be able to incorporate into its final colour, so it will appear to have water behind it when it blends onto the opaque geom. The problem is knowing how far you are from the sea floor - perhaps that can be fed to the shader using raycasts etc. Or perhaps you know your stuff will always be some distance from a relatively flat sea floor. I'm sure this step 2 is very confusing - you might experiment with faking stuff/tweaking by hand before going full math and trying to get all of this working.
3. The shader needs to write depth (turn ZWrite On). The ocean will use this depth later to do refraction and depth fog/scattering for water in front of the alpha surface.
4. Hope that two jellyfish do not overlap! This does not support overlapping surfaces.

This is not a robust, general solution, but could get your across the line for specific cases.

Solution E: Turn on MSAA and use alpha to coverage. I have never used alpha to coverage so I'd need to refer you to google.

Out of all the above, i think E is the only once i really believe in, but it relies on MSAA and i've never used it in practice so i cant speak to the trade offs..

What do you think? If others have ideas please add them!

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( @Midda-C - probably of interest )

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Yeah, we did notice this limitation early on, but pretty much wrote it off as a thing we'd need to live with. I don't think we'll need to display any transparent objects under water (the one thing we were we simply changed to dithered alphatest which looks better for us anyway). Solution C is interesting, though. I have wondered how using a simple bluenoise flipbook might look (not for this issue specifically, just for avoiding transparency in general). Unrelated, but I should play with that some more. :)

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Ha option C, i like it! If you do happen to experiment with this there are some GPU-friendly noise functions that might be useful for quick experiments. https://twitter.com/stormoid/status/1021397559699558401

And of course it would be very interesting to discuss any results!

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Will need to play with opt C. Right now we are doing dithering when spawning stuff or despawning things like fish where the dither into and out of existence. Works really well but have not tried it with something like persistent alpha objects like jelly or bottles.

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I think I will close this - for now - as I don't think much will be done from my side for now or in the near future, although I'll definitely keep it in mind and return to it if I have thoughts or if I see something that could be of use.

I would of course be very happy to hear any experiences you guys have if you try this stuff out, please do post back if you do.

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