I'm doing a DOPs simulation which is quite heavy, Houdini keeps crashing saying insufficient RAM (although I have 2GB), can I attach a ROP output driver and set it rendering without first cooking the simulation? Will the ROP cook each frame and write the SIM file, or do you have to simulate the whole sequence first, then output it?

Interesting question.

I've done some testing on this very subject, and it seems to me that DOPs simulates a frame, then executes the ROP, whether that means rendering an image or writing out a .sim file. It may be more efficient to first write out all the .sim files, and then go back and read them in and render the results.

Or you may find it better to write out the geometry from the simulation (by extracting it from DOPs into SOPs and then using the Geometry ROP to save that to disk). Then you can go back and render that on its own, with no DOPs overhead.

In the end I had no choice, Houdini kept crashing (I'm running under Windows…is the general consensus that Houdini under Linux is much more stable? Seems that way to me…). I laid down a ROP_output driver and just hit render….it worked! It looks like it simulates and then writes, frame by frame. Maybe be a useful tip for anyone else with a particularly heavy simulation…of course you have to re-render to tweak the sim, but if the sim takes forever anyway…..