Octane Scatter in Houdini - arbitrary 4 object limit?

[andrewprousalis]

Hi!
Am I correct in seeing that the Scatter functionality in Houdini is limited to 4 scatterable objects? In C4D, this does not seem to be the case. I'm curious if there is a technical limitation here? I has hoping to utilize the Scatter tools to get around the million-instance slowdown bug, but I'm not sure how to get around this possibly arbitrary limitation?

Thanks!

[dom_otoy]

Hey there!

So yes the octane scatter on surface/volume has a 4 object limit, this is the same in Octane standalone.
That being said you can use instancing or packed primitive instancing and this has no such limit.

For packed primitive instancing, just pack your geometry inside of your object and instance (for example with copy to points node etc). Just make sure to enable "packed primitive instancing" in the octane object settings.
The other option is to use the houdini instance object. You can use a pointcloud with typical instancing attributes (orient, pscale, scale etc) combined with an @instance attribute which contains the path to the objects to instance (for example obj/box1) (or if just a single object you can skip the @instance attribute and just use the object parameter. Turn on "point instancing" in the instance object settings to see it in the viewport.

Hope that's helpful! Will be making a video on this soon.

[andrewprousalis]

Hi Dom, thanks for the info!

I am currently using the packed primitive technique, but it's proving to be quite cumbersome to use after the point count gets over a million or so. Does this instance object with "fast point instancing" technique utilize the point cloud/octane scatter under the hood? or does it make an entry in the orbx for each instance? The trouble I'm having is that I have about a 100 or so instance types, instantiated with a count of between 100,000 and 1,000,000. If I'm not mistaken, the instance object approach would require one instance node per instance type, correct?

Thanks a bunch for the help!

[dom_otoy]

So you don't have to setup a new instance object for each type, the points can point at different objects using the @instance attribute.
The object instance method is about twice as fast to load as the packed primitive method, which is negligible with small instance counts but can make a big difference with bigger numbers. We're hoping to improve this, but for now this is how it is.
Either form of instancing uses octane scatter under the hood, they are just extracted from Houdini in different ways, thus the performance difference.

In the meantime for very large instance counts (in the millions) i very much recommend the object instance workflow (i know its more cumbersome...)

In terms of overall performance though, having many different instance types very much increases the load on the system. And Octane currently has a limit of about 19 million instances overall if you have motion blur enabled (further depends on the motion blur sample counts too). If you can decrease instance variations, that will very much improve performance.

There is some more interesting info here on instance performance (its in c4d but should mostly apply in the same way):
https://www.behance.net/gallery/161313935/Resource-Management-Findings-for-Octane-RenderC4D?locale=en_US

[andrewprousalis]

Great info here, thanks Dom!