Eevee Alpha Planes: Holdout Collection problem

Support Compositing and Post Processing
1

Hello,
I am working on a large environment render using several render layers composited together. I am rendering everything in Cycles, except for some volumetric clouds and fog set in a separate scene that uses Eevee to render the fog ( to save time rendering volumetrics) using the technique in this video. https://www.youtube.com/watch?v=aErwJVcoprc&t=249s

The problem I am running into is that I also have alpha plane trees set as holdouts in the fog collection/eevee scene and Eevee is rendering the entire object as a holdout not taking into account the material’s transparency.

I have put together a simple demonstration of the issue below.

Top: The Alpha transparency is not being taken into account when set as a holdout collection in Eevee., (notice sharp edge of the plane)

Below is rendered with cycles, notice how the alpha plane transparency of the leaf is acting as expected.

node snip
node snip946×1066 124 KB

Is there anyway around this? I do have film> transparent activated and alpha hashed on in the material properties. I am still relatively inexperienced at compositing so I apologize if this is hard to understand. Thank you for any help or advice.

2

In EEVEE You have to enable transparency per material:

3

Thanks for pointing that out, but I do in fact have alpha hashed turned on. Unfortunately that does not seem to solve the issue. To be clear the object is transparent if I simply render the leaf. The issue seems to stem from its use as a holdout collection

4

I would recommend using Alpha Clip here, and changing the threshold until the edge of the plane disappears

2 Likes
5

Hmm, yea holdout seems dont take in account alpha.

obraz
obraz1183×983 124 KB

Would that do the job for you if You would manually add eevee holdout to Your materials?

2 Likes
6

Thank you so much! I have been using Blender for years, but didn’t know you could set the material outputs differently for cycles and eevee in the same materal. I had tried duplicating my entire scene and giving them all separate holdout materials T_T but this is so much better.

Really appreciate the help :slight_smile:

7

It’s been 2 years, and HOLDOUT still does not support ALPHA in EEVEE?
Why?!