d3dx8 [6/7] Implement D3DXMatrixStack_Push

[H. Verbeet]

On 08/04/2008, David Adam <david.adam.cnrs at gmail.com> wrote:
> +    This->current = This->current +1;
> +    HeapReAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, This->matrix, (This->current +1) * sizeof(D3DXMATRIX) );
> +    if ( This->matrix == NULL ) return E_OUTOFMEMORY;

Aside from being a bit suboptimal (doing a realloc on every push),
this probably doesn't do what you want. Consider what happens to the
size of the array when you do something like push/pop/push/pop/...etc.

It would be better to keep track of the current stack size, and then
grow it by a factor (eg. 2 or 1.5) if a push would overflow the
current stack. You could also consider shrinking the array again if a
pop would make it use less than a certain percentage of the current
size (eg. a third).

You should also assign the result of HeapReAlloc() to This->matrix
again. Although it's quite possible for HeapReAlloc to just grow the
current block without changing its location, there's no guarantee it
will. The NULL check is useless this way.