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View Full Version : Bullet Dynamics "How to speed up calculations"



jboudreau
04-07-2013, 03:07 PM
Hi Guys

I have a scene where a coffee cup falls into a pile of coffee beans. If I just run bullet dynamics on the cup alone with no coffee beans in the scene the calculations are almost real time (I can play it back real time on the time line no calculation process at all. As soon as I add the coffee beans to the scene the calculations get really slow even though I never added dynamics to the coffee beans yet. Why would this be?

Here are the issues I have come across using bullet dynamics

- When you add geometry to a scene with dynamics even though that new geometry has no dynamics attached to it the calculations are extremely slow but are really fast if you delete the new geometry from the scene.

- When you have two objects with dynamics enabled on both objects when you disable the dynamics in the items properties panel the calculations are slow like it's still calculating for the extra geometry even though dynamics is disabled.

- When you use (shape - Convex pieces for example on the coffee beans for this example) every time you open up your scene or just switch from layout to modeler with the hub running even though you make no changes to the geometry for this case the coffee beans layout starts converging the geometry again which takes quite a bit of time.

Has anyone else came across any of these issues

Thanks,
Jason

dwburman
04-10-2013, 12:08 PM
How many polys are the coffee beans. Does the scene play smoothly with all dynamics turned off?

jboudreau
04-10-2013, 12:41 PM
How many polys are the coffee beans. Does the scene play smoothly with all dynamics turned off?

Hi

Thanks for the response

The coffee beans are 117320 polygons. The scene is made up of dynamics. The cup falls on top of the beans. If I turn off all dynamics their won't be anything to play back. The scene responds very fast when no dynamics are added. No issue with polygon count or anything like that.

Thanks,
Jason

LW_Will
04-10-2013, 03:14 PM
Can't you instance the beans?

jboudreau
04-10-2013, 06:23 PM
Can't you instance the beans?

Hi

I'm not 100% sure but I don't think you can use instances with bullet dynamics.

Thanks,
Jason

dwburman
04-10-2013, 11:25 PM
I'd suggest using one of the collision shapes that don't require a mesh evaluation on the beans (perhaps sphere or capsule), but that's not the main issue you're asking about and I don't know if that'd work with you bean shapes.

jboudreau
04-10-2013, 11:30 PM
I'd suggest using one of the collision shapes that don't require a mesh evaluation on the beans (perhaps sphere or capsule), but that's not the main issue you're asking about and I don't know if that'd work with you bean shapes.

Yeah it's not really the issue of how slow it is calculating. The issue is more that when I just have the cup in the scene the dynamics are super fast but slow down as soon as I add other objects to the scene. The other object don't even have dynamics added to them so it makes no sense why it would slow down the scene and calculations.

Thanks,
Jason

Surrealist.
04-11-2013, 04:50 AM
It sounds like a bug or weak feature/something not quite right. Sounds like it is considering all of the geometry in the scene for the calc which is not right. I would report it with scene examples. Also try and upload some kind of scene here to see if anyone can repeat it, try and determine if it is universal or just in your case.

jboudreau
04-12-2013, 03:53 AM
It sounds like a bug or weak feature/something not quite right. Sounds like it is considering all of the geometry in the scene for the calc which is not right. I would report it with scene examples. Also try and upload some kind of scene here to see if anyone can repeat it, try and determine if it is universal or just in your case.

Yeah I think it is a bug.

The problem I am having is If I am using the hub and I go into modeler to make a simple change to the texture (UV MAP) of the coffee cup in the scene and save my object. When I go back into layout the decomposing starts all over again and so does the simulation. Why would a texture change effect the simulation or the convex pieces makes no sense and it's a real pain to work with. It makes it almost impossible to work back and forth between modeler and layout because the decomposing and simulation keep calculating all the time.

Another example say I go and model a new object in modeler and save the object as soon as I go back to layout decomposing and the simulation start all over again.

I'll upload a test scene in a few days.

Thanks,
Jason