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 executes command buffers when the screen-space mask render target is set and cleared, and the shadow cascade parameters are set. Note that the shadow mask is not yet computed.