public void LoadHairShader(string path_to_cso)
    {
        // release existing shader
        if (m_sid)
        {
            HairWorksIntegration.hwShaderRelease(m_sid);
            m_sid = hwShaderID.NullID;
        }

        // load shader
        if (m_sid = HairWorksIntegration.hwShaderLoadFromFile(Application.streamingAssetsPath + "/" + path_to_cso))
        {
            m_hair_shader = path_to_cso;
        }
    }
 public static extern bool hwShaderRelease(hwShaderID sid);
 public static extern bool hwShaderReload(hwShaderID sid);
 public static extern void hwSetShader(hwShaderID sid);