How fog of war works

This page walks through what actually happens when a token moves on a fogged scene, what role walls play, and how the edge of a reveal is shaped.

The reveal flow

When a token moves on a scene with fog of war:

1. The engine computes the token’s visibility polygon — the shape of the area it can see, which is a circle (or cone) clipped by any walls in the way.
2. That polygon is stamped into the fog texture, erasing fog inside it.
3. The newly-revealed area stays revealed, even after the token moves away.

So as a token walks down a corridor, the fog peels back wherever it can see — not just where it currently is.

Walls clip the reveal

If there’s a wall between the token and what it would otherwise see, the wall stops the reveal. The wall casts a shadow into the fog and the area beyond stays black.

This is what creates the “exploring a dungeon” feel — the player can see into the room they enter, but not through the wall to the room beyond.

The polygon is computed live: every frame the engine runs ray-casts from the token’s position out to its vision range, and any wall they hit truncates the ray. The resulting closed polygon is the shape that gets revealed.

Tip

Detection modes like Blindsight and Truesight bypass walls entirely. A token with Blindsight reveals fog through walls within its blindsight range. See Detection modes.

Soft vs hard reveal edges

The shape of the revealed area’s edge depends on the token’s Edge softness setting (Vision section of the token’s Settings dialog):

• Edge softness 1 (default) — soft radial fade at the edge. The reveal looks natural, with fog gradually returning at the rim.
• Edge softness 0 — hard cut at the edge. The reveal is a crisp boundary, like a paper cut-out.
• Intermediate — partial fade band near the rim.

Use a hard edge when you want the boundary to feel definite (an arcane sphere of vision). Use soft for naturalistic exploration.

The same edge softness drives light-driven fog reveals — see Light-driven reveal.

The fog tool — manual paint, erase, reveal-all

Sometimes you want to reveal or hide fog manually as the GM. The Fog tool in the toolbar (shortcut F) gives you three operations:

Operation	What it does
Reveal area	Draw a polygon to clear fog inside it.
Apply fog	Draw a polygon to re-fog an area (paint fog back on).
Reveal all	Clears fog over the whole map. Useful when starting an outdoor encounter where everyone can see everything.

These overlap with movement-driven reveal — manually revealing a room before the players arrive lets you skip the “exploration” beat for areas that don’t need it.

Persistence

Fog state saves with the scene. Closing and reopening the scene restores the explored areas. If you want to “reset” exploration:

1. Open the Fog tool.
2. Use Apply fog with a large polygon, or use the slash command for full re-fog.

Or paint over selectively to reset only certain rooms.

Multiplayer / players seeing fog

Each player’s fog view is the shared scene fog — when one player’s token reveals an area, every player sees it as revealed. (PostRoll currently has shared fog; per-player fog is on the roadmap.)

The GM sees through the fog regardless. On the GM view, fogged areas appear as a light dim overlay rather than full black, so the GM can prep ahead of the party.

Related

• Light-driven reveal — make a scene light contribute to fog reveal even without a token.
• Fog memory — keep explored-but-unlit areas dimly visible.
• Detection modes — which token senses bypass walls (and reveal through them).