Simulation Statistics

Interface

In this section we will have a quick look at the statistics information that PhysX collects every simulation step. Usually, this information can be explored in the PhysX Visual Debugger (OmniPVD) (see Omniverse Visual Debugger) but we do offer a PhysX API method as well to allow applications to access the data directly.

After a simulation step and a call to PxScene::fetchResults(), the simulation statistics for the processed step can be retrieved through the PxScene::getSimulationStatistics() interface. The method copies the data to a user provided PxSimulationStatistics structure. For details about the individual members please refer to the API documentation.

Note

Do not fetch the simulation statistics while the simulation is running.

Usage

The provided simulation statistics is mainly meant to help investigate performance issues. It provides a quantitative summary of the work done, i.e., the number of objects or combination of objects which have been processed in the current simulation step. For example, if you encounter performance spikes in certain frames, then the simulation statistics might give some insight into possible causes. For instance:

  • Has a large amount of volumes been added or removed from the broadphase in one single step? You could try to distribute the addition/removal of objects over a couple of simulation steps.

  • Are there suddenly many more collision pairs processed than expected? This could be caused by a badly configured collision pair filter or maybe some PxPairFlags have been accidentally raised.

  • etc.

Please keep in mind that the simulation statistics are currently less a measurement of what the scene contains but rather what got processed. So it is only partially helpful to detect whether objects have been configured and arranged properly.

Example code to get simulation statistics:

PxScene scene;

// Do simulation...
// scene().simulate(...)

scene.fetchResults(true);

// Now we can extract the data from the last simulation step
PxSimulationStatistics st;
    scene().getSimulationStatistics(st);

printf("Number of dynamic bodies : %d",st.nbDynamicBodies);

For more fine grained statistics please use PhysX Visual Debugger (OmniPVD) (see Omniverse Visual Debugger)