D3DXComputeBoundingSphere和D3DXComputeBoundingBox

函数D3DXComputeBoundingSphere和D3DXComputeBoundingBox分别计算出一个物体的外接球和外接体；使用D3DXComputeBoundingSphere和D3DXComputeBoundingBox计算Mesh对象的边界；边界范围接近对象真实的边界，可加速碰撞检测等计算。

函数原型如下；
HRESULT WINAPI D3DXComputeBoundingSphere(
    const D3DXVECTOR3 *pFirstPosition,
    DWORD NumVertices,
    DWORD dwStride,
    D3DXVECTOR3 *pCenter,
    FLOAT *pRadius
);

HRESULT WINAPI D3DXComputeBoundingBox(
    const D3DXVECTOR3 *pFirstPosition,
    DWORD NumVertices,
    DWORD dwStride,
    D3DXVECTOR3 *pMin,
    D3DXVECTOR3 *pMax
);

包围体：
struct BoundingBox
{
    BoundingBox();
    bool isPointInside(D3DXVECTOR3& p);
    D3DXVECTOR3 _min;
    D3DXVECTOR3 _max;
};

struct BoundingSphere
{
    BoundingSphere();
    D3DXVECTOR3 _center;
    float _radius;
};