ka1nong

Results 4 issues of ka1nong

![image](https://user-images.githubusercontent.com/11147147/117263137-8da13300-ae84-11eb-832e-b19147cd761c.png) dynamic actor set all material->setFlag(PxMaterialFlag::eDISABLE_FRICTION, true); the crash is in the place shown in the picture

Since MBP is a multi-SAP implementation, why MBP does not perform as well as SAP when most objects sleep. My scene is too big, there are very few dynamic objects,...

raycast、swwwp、overlap and simulation.will there be a noticeable difference in their performance?Is there any relevant article to explain? thx