render elements alpha

Krakatoa for 3ds Max
1

hey all,

I am trying to use a custom render element but am running into a problem with the alpha channel(it seems to be the same with other kraka elements aswell). My beauty pass alpha doesnt match the element alpha.It looks to me like the Density Exponent isnt being calculated with the element, cause if i set the exponent to 0 the alphas match. Is there a workaround for this or some nodes i should connect in magma ?

cheers,

Craig

2

As far as I know, this is not a bug. The Render Elements save a SOLID alpha because they accumulate particles without blending. The Render Elements will draw particles on top of other particles, so if a pixel had 10 particles influencing it in the Beauty channel, the RE will show only the CLOSEST particle to the camera, overwriting all others. This is because data like Z-Depth and Normal make no sense if blended together or anti-aliased.
Since Krakatoa is a Volumetric renderer, the concept of Render Elements is slightly foreign to it, and it outputs its RE data as a sort of “closest surface” representation instead of “volume”. The correct way to do this would be using some sort of Deep Compositing data where the values are represented along each view ray, but right now Krakatoa does not support that (in fact, no renderer supports this yet since WETA and ILM are still figuring out the correct workflow).

3

thanks Bobo,

hmm … I was wondering if it were a bug or something like this was the answer.

I understand there is no need for anti-aliasing but it just seems a little odd that if particles that are no longer closest to the camera are rendered in the element and are no longer there when the density exponent is used . The way my brain is seeing it is the particles that are deeper in the volume will be affected by colors in the element that were closer to the camera.

I hope that makes sense!

I’ ll run a check and render a custom pass as an element and then do a seperate render with the same flow and render a beauty with KCM overide and see if it makes any difference to the compositors.

cheers,

Craig

4

I just did a test and it makes a huge difference to compositing.

So is there a way to have multiple beauty passes with one render ? or is the only real option to save to disk then render all the passes with a PRT loader ? :frowning:

cheers,

Craig

5

Nope, you will need some form of Render Pass Manager to do that, and it will be a separate render for each.
I am not 100% sure what exactly you expect to output from the multiple Beauty passes, can you provide a short bullet list that explains your needs?

6

I just need to give the compositors something they can play with or else they’ll complain that they cant do thiks or that.

  • red to blue color by speed,
  • custom normal pass that comes out as expected (apart from depth issue sometimes the krakatoa colors come out a bit funky).
  • RGB positon pass.
  • depth pass

like I say it seems to be a problem with render elements that they render particles that are not there any more, as they dont take into account the density exponent.

try it yourself render with a custom element and then render the same pass as a beauty with a KCM overide and see the difference when you set a matte in composite.(obviously you need to try with the density exponent less than 0)

Craig

7

Those particles are there. If you don’t see them because they aren’t dense enough, cull them. It makes the render faster.

As to your listed passes, “will it blend?” No. They only way those would is if your beauty pass was rendered with super high density.

8

thanks for your time Chad and Bobo,

i’ll just have to render multiple beauty passes until the render elements become more useable.

Craig

9

Because you are changing the per-particle data, a render elements may not be the way to go, but a render pass system.