Memory usage

[riptide]

I'm usinge Bullet physics in an iPhone game. It appears to really be pushing the limits of memory in my iPhone application -- creating an instance of btDefaultCollisionConfiguration appears to allocate ~40 Megabytes of memory. On an iPhone application, that just won't fly. Is there any way to reduce the memory usage of the collision configuration? A different config class or something? Forgive me, I know little about how Bullet functions internally.

Thanks,
- Marcus

[riptide]

Figured it out.
Usually, when initializing Bullet, there is code that looks something like this:

Code: Select all

collisionConfig = new btDefaultCollisionConfiguration();

Changing it to something like this works well:

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btDefaultCollisionConstructionInfo constructionInfo = btDefaultCollisionConstructionInfo();
constructionInfo.m_defaultMaxCollisionAlgorithmPoolSize = 1023;
constructionInfo.m_defaultMaxPersistentManifoldPoolSize = 1023;
collisionConfig = new btDefaultCollisionConfiguration(constructionInfo);
...

The defaults for MaxCollision and PersistentManifold pool sizes are 65535 each. When the construction info is set to the above values, memory usage appears to spike to around 8Mb and levels out at around 6Mb in my program which is very simple. That leaves plenty of memory for the rest of my game.

Hope this helps someone.
- Marcus

[Erwin Coumans]

Good point.

The default memory pools of Bullet 2.72 were way too big, so your solution is fine. You can also set the stack allocator usage to zero, reducing it by another 2Mb. Note that Bullet automatically switches from pool to dynamic memory allocations, so it is safe to use smaller defaults.

Upcoming Bullet 2.73 has much smaller pools in btDefaultCollisionConstructionInfo:
m_defaultMaxPersistentManifoldPoolSize(4096),
m_defaultMaxCollisionAlgorithmPoolSize(4096),
m_defaultStackAllocatorSize(0)

http://code.google.com/p/bullet/source/detail?r=1482

Thanks for the feedback,
Erwin

[sparkprime]

I've seen issues about configuring bullet for low memory platforms come up a couple of times, it might be a good idea to write a wiki page about it

[Erwin Coumans]

The new default lower memory pre-allocation will reduce the number of reported issue for iPhone etc.

But we definately need to document how to manage memory in the Wiki, doxygen and Bullet user manual.
Thanks,
Erwin