ZBufferParams

    static public Vector4 GetZBufferParams (this Camera cam)
    {
        var type = graphicsDeviceType;
        float near = cam.nearClipPlane;
        float far = cam.farClipPlane;
        float x, y, fn = far / near;

        if (type == UnityEngine.Rendering.GraphicsDeviceType.OpenGLES2 ||
            type == UnityEngine.Rendering.GraphicsDeviceType.OpenGLES3 ||
            type == UnityEngine.Rendering.GraphicsDeviceType.OpenGLCore)
        {
            x = (1f - fn) * 0.5f;
            y = (1f + fn) * 0.5f;
        }
        else
        {
            x = 1f - fn;
            y = fn;
        }
        return new Vector4(x, y, x / far, y / far);
    }