ディレクショナルライトのスクリーン空間のシャドウマスクが計算される前
Directional lights when using non-mobile shadows "gather" shadowmap into a screenspace buffer and do PCF filtering
during this step. Later on actual object rendering just samples this screenspace buffer.
This light event will execute command buffers when the screenspace mask render target is set and cleared, shadow cascade parameters are set, but the shadow mask is not computed yet.