By now, to keep the mask face the screen, i used WorldPos * ViewProjectionTransform output to calculate the mask position.
It worked well in NME,
but not well in project.
Beacause the mask position value is based on the world position, when mesh moved, mask did not, so i come here ask for help.
Hope the mask face the screen and keep its position following the mesh.
Reason for [face the screen]：To keep the inside things visible at any camera angle through the mask.
Reason for [follow the mesh position]：To filter out the correct shield position when mesh moving.