Hey everybody,

Went head first into Karma with my latest project which is just a camera path animation working it's way through textured planes of which some are sequences. Hopefully these are obvious questions from my lack of experience with Karma. Oh I am not using solaris but using the 'new' direct method of just using a ropnet Karma node. (but did some quick small tests with solaris and seemed not to make a difference)

- most important for this project was the intersections of image planes which creates an alpha 'line' where they intersect. Tried the same in Mantra and looks fine.

https://www.jottacloud.com/s/255a044f57014bc41a085b89f16f7dfbdc4 [www.jottacloud.com]

- scratched my head to create just a plain alpha aov.

- so cryptomatte to the rescue. Works great... exept no denoising. Weirdly enough it does denoise in the preview.

- image sequences do not refresh correct most of the time in the viewport especially when you use more than one. They show as white blocks making it impossible to see the rest of the scene. They work fine at rendertime by the way.

Laters, Szann

Cannot imagine nobody has encountered any of these basic issues...

szann
- most important for this project was the intersections of image planes which creates an alpha 'line' where they intersect. Tried the same in Mantra and looks fine.

There's not much you can do about that. It looks like its ray bias--each transparent part of the plane is tracing to the next intersection, but it starts raybias distance away. This can cause it to start the trace from outside the next hit. The only remedy is to use a ray bias that is small enough. The gap will be there but hopefully will be too small to see. The better option is to not place transparent edges coplanar to other edges. Leave a gap at least as large as the ray bias.

jsmack
There's not much you can do about that

Mantra is clearly doing something about it, it doesn't skip the bottom plane even with very large ray bias
In fact Mantra doesn't seem to use global ray bias for opacity samples at all

tamte
Mantra is clearly doing something about it, it doesn't skip the bottom plane even with very large ray bias
In fact Mantra doesn't seem to use global ray bias for opacity samples at all

yeah, Karma is clearly treating opacity samples differently than mantra. It seems like they are actually refraction.

I think the ray bias only affects Mantra in ray trace mode from memory, could be wrong though.

Thanks for mentioning the ray bias. It doesn't completely solve the problem but works in most cases.

Info from the source itself:

This is due to the intersector used by karma applying ray bias when it's continuing rays after hitting partially opaque surface. Mantra doesn't have this issue because it collects all intersections in one go. Unfortunately this behaviour in karma is unlikely to be changed any time soon. However, you can adjust ray bias and reduce its value until the artifacts are no longer visible. (If you're using Houdini build 19.0.458 or newer, you can try setting it to 0)

I updated Houdini to .458 and indeed a ray bias setting of 0 works

Oh and in .458 the refresh of the animations in the viewport is way better. Not 100 but at least no more full white blocks. Very workable now.