I followed this video to get a simple opacity shader: https://youtu.be/dMzXXqO8kWw
However, it requires the mask to be a texture, that needs to be saved in the game files. I don't want to have any more textures than needed, and would much prefer to make this using a tileset or something similar, for the sake of disk space and ease of use (i wouldn't need to copy every single shape of a room in a graphics program). Is there a way to do such a thing?
If I left out some important info, please let me know.