Is it safe to use the same parameters for input and output in D3DX functions?
Using the D3DX library that is a part of directX, specifically directx9 in this case, I'm wondering if it's safe to use the same matrix (or vector etc) for input and ouput
D3DXMATRIX mat;
D3DXMatrixInverse(&mat, NULL, &mat);
I've been avoiding doing so, assuming 开发者_如何学JAVAthat it would result in bad things happening when parts of the array got partly overwritten as results are calculated but I see an awful lot of code around that does exactly this.
A brief test indicates that it seems to work ok, so I'm assuming that the D3DX functions take a copy where necessary of the input data, or some other method to ensure that this works ok, but I can't find it documented anywhere so I'm reluctant to rely on it working.
Is there any official statement on using the functions like this?
Yes, it is. From msdn:
Each of the functions can take the same object as the passed [in] and returned [out] parameters
I'm pretty sure the answer is yes. I can't find anywhere where this is said for sure however ...
Edit: Flicking through D3DX9Math.inl it looks like care HAS been taken to make sure you can. For example if we look at the code for D3DXVec3Cross:
D3DXINLINE D3DXVECTOR3* D3DXVec3Cross
( D3DXVECTOR3 *pOut, CONST D3DXVECTOR3 *pV1, CONST D3DXVECTOR3 *pV2 )
{
D3DXVECTOR3 v;
#ifdef D3DX_DEBUG
if(!pOut || !pV1 || !pV2)
return NULL;
#endif
v.x = pV1->y * pV2->z - pV1->z * pV2->y;
v.y = pV1->z * pV2->x - pV1->x * pV2->z;
v.z = pV1->x * pV2->y - pV1->y * pV2->x;
*pOut = v;
return pOut;
}
You can see that it performs the cross product into a temporary and THEN, in the final step, it copies it into the return. It would be nice if this was stated somewhere for sure.
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