Vision & Lighting

Reference values and rules used by Mimir’s fog of war calculation.

For the toolbar controls, see Play Mode. For step-by-step usage, see Fog of War. For the design rationale, see Vision System.

Scale

One grid square equals 5 feet. All ranges below are in feet and converted to map pixels using the map’s grid size.

Token Vision Values

Each token carries four vision-related values:

Value	Meaning	Notes
Bright vision	Sight range in bright light	Unset = unlimited
Dim vision	Sight range in dim light	Unset = unlimited
Dark vision	Sight range in darkness	0 = blind in darkness; 60 ft = typical darkvision
Light radius	Dim radius of light the token carries	0 = no light; bright radius is half the dim radius

Ambient Light Levels

Level	Description	Vision range used
Bright	Daylight, well-lit rooms	Bright vision (usually unlimited)
Dim	Twilight, torchlit edges	Dim vision; rendered as dim sight
Darkness	Underground, night	The larger of dark vision and the token’s own light radius; darkvision counts as dim sight

The ambient level initializes from the map’s UVTT data when present and can be overridden per session from the map toolbar.

Light Source Presets

Source	Bright Light	Dim Light
Candle	5 ft	10 ft
Torch	20 ft	40 ft
Lantern	30 ft	60 ft
Spell / Custom	20 ft	40 ft (defaults; editable)

Token-carried light uses the token’s light radius value as the dim radius, with the bright radius at half that distance.

Light Level at a Point

The effective light level at a point is the best of:

Bright, if the point is within any active source’s bright radius
Dim, if the point is within any active source’s dim radius (when ambient is darkness)
The ambient level otherwise

A token must be inside a light’s radius to benefit from it: the light level at the token’s own position determines which vision range applies.

What Reveals Fog

Token	Reveals fog?
PC token, visible to players	Yes
PC token, individually hidden	No
NPC token	No
Monster token	No

The Fog and LOS toggles are separate buttons but not fully independent: enabling Fog forces LOS on, and the LOS button is locked until Fog is turned off. Reveal Map overrides both. The resulting states:

State	Map (player view)	Tokens (player view)
Fog off, LOS off	Fully visible	All player-visible tokens shown
LOS only	Fully visible	Only tokens within party line of sight
Fog on (LOS forced on)	Hidden outside party vision	Only tokens within party line of sight
Reveal Map	Fully visible	All player-visible tokens shown

Individually hidden tokens are never shown to players, in any state. See Play Mode for the controls themselves.

Wall Occlusion

UVTT maps include wall and portal (door) data:

Vision is computed as a visibility polygon by raycasting against walls
Closed doors block vision; open doors do not
The Fog and LOS toggles are only available on maps with UVTT data

Maps without wall data use circular (radius-only) vision with no obstructions.

Mimir - D&D Campaign Assistant