public void LoadHairShader(string path_to_cso)
    {
        // release existing shader
        if (m_hshader)
        {
            HairWorksIntegration.hwShaderRelease(m_hshader);
            m_hshader = hwHShader.NullHandle;
        }

        // load shader
        if (m_hshader = HairWorksIntegration.hwShaderLoadFromFile(Application.streamingAssetsPath + "/" + path_to_cso))
        {
            m_hair_shader = path_to_cso;
        }
#if UNITY_EDITOR
        RepaintWindow();
#endif
    }
 [DllImport("HairWorksIntegration")] public static extern void          hwSetShader(hwHShader sid);
 [DllImport("HairWorksIntegration")] public static extern bool          hwShaderReload(hwHShader sid);
 [DllImport ("HairWorksIntegration")] public static extern void          hwSetShader(hwHShader sid);
 [DllImport ("HairWorksIntegration")] public static extern bool          hwShaderReload(hwHShader sid);
 public static extern bool hwShaderReload(hwHShader sid);
 public static extern bool hwShaderRelease(hwHShader sid);
 public static extern void hwSetShader(hwHShader sid);