Author Topic: Daily Builds 1.7  (Read 166867 times)

2017-08-15, 12:25:32
Reply #300

PROH

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I've had this alpha problem in v1.6.1 also.

2017-08-15, 13:45:32
Reply #301

Frood

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I think this is correct. Refraction "sees" environment there (something we would love to have for masks :) And the solid plane is just not enough to cover all refraction directions. If you would put a semisphere above the scene, alpha should get solid white.


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2017-08-15, 15:30:17
Reply #302

PROH

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Yes, the refraction "sees" the environment as you describe, but it doesn't "see it" in the viewers direction, and therefore you can't use the alpha channel as a mask for replacing the background.

2017-08-15, 15:55:50
Reply #303

Ludvik Koutny

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Making refraction always produce opaque alpha would be devastating for some of the compositing workflows. What's on the picture is correct - there's environment being refracted, and environment has 0 alpha.

If you want to override it, just select your glass material, and in advanced options rollout, set alpha mode to always white.

2017-08-15, 16:52:34
Reply #304

PROH

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I'm do not want refraction to always produce opaque alpha. Just saying that when there's solid geometry behind your glass, water or whatever refractive material, the alpha behavior is not always logical or even "correct". The workaround you suggest doesn't always work either, when for example the refractive object is placed partly in front of solid geometry, and partly in front of the background.

In most cases it's not a big problem to fix it in PS tho.

2017-08-15, 19:11:02
Reply #305

Fluss

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The alpha channel should be white in this case, nothing else.

2017-08-15, 20:37:34
Reply #306

naeq

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Probably you guys right, probably it's correct, but in most cases in my professional projects, alpha like that makes only problems.
Maybe there should be a trigger in material for solid alpha in refraction?

2017-08-15, 21:34:32
Reply #307

Ludvik Koutny

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Come on guys, did you even read my post entirely? :)

In the advanced options rollout of CoronaMTL, there is an alpha mode dropdown, that allows you to override alpha of your glass to pure white (opaque alpha)


2017-08-15, 23:58:58
Reply #308

naeq

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This doesn't solve entire problem. I've attached image that should explain what we're looking for.
Anyway, alphas for refraction are little too solid in my opinion.

2017-08-16, 01:25:32
Reply #309

shortcirkuit

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hey guys - what is this feature in the latest daily?

Added support for scripted light plugin rendering

2017-08-16, 08:49:31
Reply #310

Ondra

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it is for when you extend corona light by  maxscript. lumiere is using  that
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2017-08-16, 08:52:16
Reply #311

romullus

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This doesn't solve entire problem. I've attached image that should explain what we're looking for.
Anyway, alphas for refraction are little too solid in my opinion.

Corona is tracing alpha according to material's IOR and the laws of physics, you're expecting to get some arbitrary alpha, based on your feelings, mood or whatever else. How on earth renderer could guess what alpha you're expecting at specific situation in given moment of time?

As for your example, you could try to decrease Max Ray Depth to very low value, like 1-3 and see if that would help to get rid of unwanted refractions in alpha. Unfortunatelly that would inevitably degrade beauty pass as well.
I'm not Corona Team member. Everything i say, is my personal opinion only.
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2017-08-16, 09:08:28
Reply #312

Njen

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Yeah, there's a solid plane behind that diamond.

Not if parts of the environment being refracted have no alpha.

2017-08-16, 09:44:55
Reply #313

Fluss

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alpha and refraction are NOT the same. Naeq example is good.

The real question is : is that usefull for compositing ? It's not. The composited background will not be affected by IOR so it's useless.

2017-08-16, 11:19:11
Reply #314

Ludvik Koutny

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alpha and refraction are NOT the same. Naeq example is good.

The real question is : is that usefull for compositing ? It's not. The composited background will not be affected by IOR so it's useless.

You seem to be unable to see further than the boundaries of your own workflows. There are quite a few compositing packages, such as fusion, which allow you to import geometry and put realtime GPU computed refraction on it, then use that to refract the background added on postprocessing and mask it out by alpha which takes refracted environment opacity into account. And there are some pipelines that rely on it.

The exact same thing that's happening here in Corona is happening also in V-Ray, when you set refraction to affect alpha channel. And V-Ray has been used for quite many feature films in quite many VFX pipelines, and they don't get people complaining about this behavior, because it works as intended.

I am not implying that everything V-Ray does is right, but in this particular case, it is.