Bounce light on matte objects?

[Njen]

I want to make an object matte (black in RGBA channels), and I can't figure out how to do it.

The closest I've come to it is to put a shadow catcher material into a rayswitch, but I still see bounce light affecting the shadow catcher object.

Is there really no way in Corona to make an object matte? Or am I doing it wrong?

[Njen]

I think I've found a workaround for now: light material set to black with 'Visible to alpha channel' off. But I'm worried that this is some sort of hack and may actually cause problems on other ways.

If there is no native way to make an object matte, Corona really needs one, preferably by some sort of object property, or even a setting in the renderer to add objects to a list that makes them matte.

Doing it by a material creates all sorts of complications when attempting to set up multiple passes to render different layers because now I have to account for swapping materials using scripts.

[maru]

I can confirm the thing with shadow catcher catching GI even if it's set to 100% black, but I think this might be the intended behavior - since you always want to catch GI on the backplate, and that's how the shadowcatcher should be used.

The easiest solution I can think of to get an object which is 100% black in beauty and alpha is to make a standard Corona mtl, set diffuse color to black, and "alpha mode" to "always black". Is this what you need? Is it still too complex/too many clicks to set up?

[Njen]

That also works as a work around, thanks :)

I still would rather prefer an object property that when enabled makes an object matte similar to how other renders work.

[Njen]

I don't know why it's taken me so long to get back into this issue, but I've just realised that none of these options work, as none of them properly cut out the alpha channel. So unless I'm mistaken, there is no way to properly matte an object in Corona?

[maru]

Not sure how exactly you are doing this, but here is what should happen in 1.7 hf2 when using Corona mtl or Rayswitch mtl.
Please explain if this is about something else.

[Njen]

Oh, it seems that this daily build produced the issue:
Corona_2018-01-16.exe

Reverting to 1.7 hf2 produces the intended result.

Do you know if this is fixed in later daily builds?

[maru]

Oh, it seems that this daily build produced the issue:
Corona_2018-01-16.exe

Reverting to 1.7 hf2 produces the intended result.

Do you know if this is fixed in later daily builds?

I have just confirmed this issue with the newest daily build, and reported this to our devs. We also have an open case where the shadowcatcher is always white in the alpha regardless of it's mode, so it seems these two may be related. Both will be definitely fixed ASAP.

[Frood]

so it seems these two may be related.

Maybe these three:

+ https://corona-renderer.com/bugs/view.php?id=2954


Good Luck

[Njen]

Ahh, good to know this is confirmed.

The silly thing was that when we talked about this issue eariler in the thread, in the back of my mind, I thought we did in fact solve my dilemma. But when I saw the results in the daily build I discounted those thoughts.

Thanks!

[maru]

In the newest daily build everything is working as expected now. (all shadowcatcher modes, refractive material in thin mode, alpha always black mode)

[maru]

Just a small update on the matter:
-Matte objects will be redone at some point in the future - currently we don't have any specific timeframe, so it's definitely not expected for v3 or v4
-There is a "shadow amount" parameter in the Corona Shadow Catcher Material - in case of some issues (e.g. catching too much GI), you can try increasing this value to max (10) - it should get rid of all/most GI.