Bullet Physics on Wii

[vswbmw]

I've used Bullet Physics to implement collision & dynamics parts of unannounced Wii game.
And I would like to describe some issues and advantages which I have encountered.

1. Data aligning & ATTRIBUTE_ALIGNED16 usage
Bullet use ATTRIBUTE_ALIGNED16 macro to align data e.g.

Code: Select all

ATTRIBUTE_ALIGNED16(class) btVector3
{
...
};

On most (non win32) platforms this gives result:

Code: Select all

class __attribute__ ((aligned (16))) btVector3
{
...
};

But on metroworks wii compiler, code above does not align the data.
To align data we must write something like this:

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class btVector3
{
} __attribute__ ((aligned (16)));

For our build I was defined macro like EXTRA_ATTRIBUTE_ALIGNED16 in btScalar.h and use it after class closing brace:

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#if MYPLATFORM
#define EXTRA_ATTRIBUTE_ALIGNED16 __attribute__ ((aligned (16)))
#define ATTRIBUTE_ALIGNED16(a)    a
#endif
ATTRIBUTE_ALIGNED16(class) btVector3
{
...
} EXTRA_ATTRIBUTE_ALIGNED16;

I'll post other issues later. Maybe there is some mistakes, anyway it works in my current build

[Erwin Coumans]

Have you tried

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#ifdef MY_PLATFORM
#define ATTRIBUTE_ALIGNED16(a) a __attribute__ ((aligned (16)))
#endif //MY_PLATFORM

ATTRIBUTE_ALIGNED16(btVector3) should expand to

Code: Select all

class btVector3
{
}__attribute__ ((aligned (16)));

which works fine for gcc compilers etc.

Thanks,
Erwin

[kester]

Hi,

We did the same thing, only named it ATTRIBUTE_ALIGNED16_BEGIN and ATTRIBUTE_ALIGNED16_END:

The only effect of the aligned attribute on Codewarrior is to pad the structure - it doesn't call any aligned allocators.

[vswbmw]

Have you tried

Code: Select all

#ifdef MY_PLATFORM
#define ATTRIBUTE_ALIGNED16(a) a __attribute__ ((aligned (16)))
#endif //MY_PLATFORM

ATTRIBUTE_ALIGNED16(btVector3) should expand to

Code: Select all

class btVector3
{
}__attribute__ ((aligned (16)));

which works fine for gcc compilers etc.

Thanks,
Erwin

Thanks for reply, how ATTRIBUTE_ALIGNED16(btVector3) expands to

Code: Select all

class btVector3
{
}__attribute__ ((aligned (16)));

When I can write ATTRIBUTE_ALIGNED16(btVector3) to do this?
Somewhere in class declaration? In Bullet on gcc this macro used as:

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ATTRIBUTE_ALIGNED16(class) btVector3
{
...
};

and expands to

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class __attribute__ ((aligned (16))) btVector3
{
...
};

Or I am not right?

[vswbmw]

Hi,

We did the same thing, only named it ATTRIBUTE_ALIGNED16_BEGIN and ATTRIBUTE_ALIGNED16_END:

The only effect of the aligned attribute on Codewarrior is to pad the structure - it doesn't call any aligned allocators.

We're using custom memory allocator which supports aligned allocations & call btAlignedAllocSetCustomAligned to override bullet allocator functions and define BT_HAS_ALIGNED_ALLOCATOR.