分形之拆分三角形（Split Triangle）

static void SplitTriangle(const Vector3& v1, const Vector3& v2, const Vector3& v3, Yreal angle, Vector3* pVertices)
{
    Vector3 dir12 = v1 - v2;
    Yreal len12 = D3DXVec3Length(&dir12);

    //Vector3 dir13 = v1 - v3;
    //Yreal len13 = D3DXVec3Length(&dir13);

    Vector3 dir23 = v2 - v3;
    Yreal len23 = D3DXVec3Length(&dir23);
    dir23 /= len23;

    Yreal len = len12*0.5f/cosf(angle);

    pVertices[0] = v2 - dir23*len;
    pVertices[1] = v1;
    pVertices[2] = v2;

    pVertices[3] = v3 + dir23*len;
    pVertices[4] = v3;
    pVertices[5] = v1;
}