void Update()
        {
            if (Context == null)
            {
                return;
            }

            // [TODO] need to consider camera distane here?


            Frame3f sceneFrameW = Context.Scene.SceneFrame;

            if (sceneFrameW.EpsilonEqual(lastSceneFrameW, 0.001f))
            {
                return;
            }
            lastSceneFrameW = sceneFrameW;

            if (AdjustShadowDistance)
            {
                // use vertical height of light to figure out appropriate shadow distance.
                // distance changes if we scale scene, and if we don't do this, shadow
                // map res gets very blurry.
                Vector3f thisW   = lights[0].transform.position;
                float    fHeight =
                    Vector3f.Dot((thisW - sceneFrameW.Origin), sceneFrameW.Y);
                float fShadowDist = fHeight * 1.5f;

                // lights need to be in-range
                if (fShadowDist < LightDistance)
                {
                    fShadowDist = LightDistance * 1.5f;
                }

                // need to be a multiple of eye distance
                float fEyeDist = sceneFrameW.Origin.Distance(Camera.main.transform.position);
                fShadowDist = Mathf.Max(fShadowDist, 1.5f * fEyeDist);

                int nShadowDist = (int)g3.Snapping.SnapToIncrement(fShadowDist, 50);

                if (cur_shadow_dist != nShadowDist)
                {
                    QualitySettings.shadowDistance = nShadowDist;
                    cur_shadow_dist = nShadowDist;
                }
            }
        }