Return of per poly simulation issues?

Version 4.9.3

It may be something I’m missing, but I though we could run physics simulations on Static Meshes when “Use Complex Collision as Simple” was enabled, along with the Physics check boxes checked (mass, simulation enabled, gravity).

Problem is, I can run into the object, but it doesn’t simulate properly when I run into it. (Won’t move)

It will move with simple collision, but I can’t really do that with my project in the long term. (need precise hits and damage for space battles with laser hits, etc)

Anyway, I thought this used to work back around 4.7 I would say? I saw some other questions where this seemed to be tackled at that time, but I may have misunderstood.

I also get a warning in message logs after PIE saying “Trying to simulate physics on “xxx” but it has ComplexAsSimple collision.”

I also saw what appeared to be something similar on one of the recent live streams or other video where they were talking about per-poly simulation and I watched the asset fall through the floor. If they were able to tweak the settings to get it to work or not I forgot. I will try and find the video and see if they got it to work and how.

Is this behavior normal? Is this expected to change? If anyone knows, that would be great.

Bump. I’m having the same issue. If anyone know’s how to solve this, please help.

DoubleBump. Me to.

Hi -

This post on the forums from one of our Physics Engineers should help explain why you cannot use “Complex as Simple” collision for physics simulations.

The static mesh complex collision uses
a regular trimesh which is passed into
PhysX. This mesh is never updated at
runtime and can be used for scene
queries as well as static collision.
The mesh is cooked offline so that
various optimizations are done, for
example building a BVH and cleaning up
vertices etc…

A simulated object cannot use this
complex collision as PhysX needs to
store various values (for example
velocity) for each vertex, and this is
way too expensive for a trimesh.

So a simple recap of this is that you can use PerPoly collision (Use Simple as Complex) for static objects and for queries on dynamic objects, but it cannot be used for dynamic objects collision because it would just be too expensive.

I hope this helps clear up why you’re getting these results.

Tim

so, does that mean that it is disabled by the engine and can be enabled with a source build?

If you’re comfortable using source you should be able to look and find where the collision is being set for this. I believe this was actually enabled in earlier versions of UE4 like 4.1 to 4.4, but I cannot remember for certain and it has been at least a year and a half since I last used those. I could be wrong though, it’s just been so long.

I believe it was as well but I can’t actually remember. I’ll have to download one or more of those builds and test with it. If I manage to enable it, I’ll report my findings to this thread. I did manage to enable auto convex collision building in my source build. However, this process takes too long to be a viable option for my particular need. Actually, thinking about it now, it may just work if I am able to run the process in another thread and am able to store the results. I’ll have to look into that as well and determine which is best for my use case. Thank you very much for your time.

Hi,

Did you manage to enable physical simulation with per-poly collisions?

I am having the same problem, but I could not found any version having this working :frowning:

Thank you!