Preset areas to be revealed

When using fog of war (the simple kind), it takes a while to reveal complex areas with polygon reveal. Is it possible to define these areas ahead of time, then quickly reveal them during gameplay?

Kinda. If you have a complicated area of Fog of War, ahead of your session, do the detailed polygon work to set the room as it will be when revealed to the players. Then cover the area with a black rectangle on the Map Layer. You can draw a filled shape using the Roll20 drawing tools or use a 10 pixel by 10 pixel JPG of a black square (that you can re-size to however big you need it). When in the game, all you have to do is switch to the Map Layer and move or delete the black rectangle and your hard work with Fog of War is revealed in an instant.

Thanks. That's exactly what I was looking for.

If you put it on the Token Layer, you can cover tokens with it also, provided none of the players can control them.

Good point, Aaron. I have been using enemies on the GM Layer so I forget about that.