Yuzhu Wu

BryanRay
I have a definitive answer! Also, the docs have been updated to clarify:

Complexity
This setting is defined by USD and Hydra to control for the number of iterations to use to render “refine-able” (subdivision) surfaces. Karma mostly ignores this setting, since it measures the surface in screen space to decide how many iterations it needs to render the surface smoothly. Instead Karma uses this setting more like a subdivision on/off switch. If this is set to Low or Medium, Karma renders the (chunky) hull. If it is High or Very High, Karma renders the (smooth) limit surface.

Other renderers (such as RenderMan or Storm) will treat this setting differently, using it to determine subdivision quality. If you need to render the same scene in Karma and another renderer, remember to use High or Very High to make sure Karma renders subdivision surfaces smoothly.

In short, if you're rendering with Karma, Medium or Low performs no subdivision or other refinements, so the memory footprint will be significantly lower, but the geometry may not be smooth enough, depending on your topology.

thanks for the reply,and all the research,I'm using arnold renderer, maybe I should ask the qustion at arnold forum, and figure out what arnold use this option for.

what the 'complexity' option at usdrender rop do? if I set it to 'Very High', and hit render, it will take all my 128g computer memory, even though the sence is not that complexity. if I set it to 'Meduim', it will take about 20g memory, and it still can render out.