Clip geo and shadowmatte

[Anonymous]

Hi all,

if I put a clipgeo material on a scene that contains a shadowmatte material I'll get strange artifacts on the alpha and on the shadows.

Here's the normal "right" scene:

..and here with the right Alpha:

But...... After putting the geoclip material on the red box, the shadows look bugged. I always get strange straight lines on the shadows on the ground plane:

..and this is the resulting alpha: it looks that the shadow matte stops working.

So.. maybe a bug or am I miss something giant under my nose 🙂 ?

I work a lot with shadowmatte.. and these artifacts with geoclip are hard to workaround.

The max file that generated this sample is here.

clip.zip

Thank you in advance!

PS: any updates coming on the GPU lack for the clipgeo and for the shadow matte?

[pproestos]

Maybe is this case?

https://www.youtube.com/watch?v=vKBEk5Wn4c8

I mean to assign a trace set to the floor...

[Anonymous]

@Petros .. sorry I forgot: this behaviour is independent from trace sets. I tried also that.
And it is also independent from excluding the shadows casting from the arnold properties.

[madsd]

Swap out the map to material with the actual Matte closure, it removes some of those glitches.

Also note, that when you insert a box to cut a plane, there is only 1 place it can sit and that is with the bottom face at the exact same location as the plane.
Else you will get edges as seen in your alpha shot.
You can also use a plane to cut another plane with a leaning on the clip geo since clip geo is a projection effect, it will trace the entire object sitting above it when only a small contact has been made.

[Anonymous]

Thank you Mads, but unfortunately i'm forced to use the shadow/matte for compositng, to separate shadows passes +diff+mask.

The main problem is that adding a geoclip shader in the scene, the plane catching the shadows stops working.

The artifacts appears also when not intersecting. And also between solid objects (= no single sided planes)

The most important fact is that if I delete the clipping object, the shadow matte will turn on " perfecting working" immediately

In this case the clipping box is floating.

.. and the alpha is 100% white.

And "a strange squared shadow" appears on the ground (bigger than the clipping box).

[madsd]

Did you try what I wrote in the first line?

[Anonymous]

Yes, but alpha looks wrong. (better, but not right to be suitable for final production renders)

In this case, I used the matte as you wrote, and this is the resulting alpha

PS: the clipgeo objects is floating

[madsd]

upload this scene, and set it so it returns the exact thing on your image when rendering.

I assume you want the box on the floor to be hidden?
Or do you want a hole there.

Upload and explain either case you want.

[Anonymous]

Here's the scene:

clip2.zip

The box floating over the floor shoud be hidden.. without affecting in that strange way the floor/shadowcatcher.

I tried to rotate some dregees the box.. but the square on the plane remains does not follow the rotation...

[madsd · Accepted solution]

I put this as a separate answer so you can potentially flag this solved.
It comes with a clause however, but you can get it working, today.

For some reason the bug, and yes there is a bug, I will note dev about this thread so they see this so it can be fixed. - is related to scene scale and units. oddly enough.

It means little to non in a practical scenario since I "corrected" it and uploaded a version of your file that works perfect as seen here:



Do note, that due to the nature of this bug, you will not be able to change your Unit settings and make the box go away, you need to have a reset max with this setup, and force converting your scene into this new Unit.
It is likely that you can use values you normally use and the error has to be found in the way you inject different Unit setups both places.

I have attached a max 2020 file that works ace.

Feel free to flag this post as accepted, and I will go and report this issue to dev now.


clip2.zip

[Anonymous]

A big bow to you, Mads! 🙂 Thank you for your precious time and help.