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@neonbasschild neonbasschild released this 12 Jun 13:36
· 4 commits to main since this release
v1.0.0
e686cd0

Day/Night Theme Switcher — FoundryVTT Module

Automatically switches the Foundry UI between dark (night) and light (day) themes based on the actual in-game sunrise and sunset times provided by Calendaria.

This means the threshold shifts with the season, the active calendar (Gregorian, Harptos, Exandria, etc.), and the climate zone of the current scene — not a hardcoded clock time.

Requirements

Module Version
Calendaria Latest
Foundry VTT v12+ (v13 verified)

Installation

  1. Copy the day-night-theme/ folder into Data/modules/.
  2. In Foundry, go to Add-on Modules and enable Day/Night Theme Switcher.
  3. Make sure Calendaria is also enabled.

How It Works

On every in-game time change Calendaria fires the calendaria.dateTimeChange hook.
The module then calls:

const sunrise = CALENDARIA.api.getSunrise(); // e.g. 6.25 → 06:15
const sunset  = CALENDARIA.api.getSunset();  // e.g. 19.5 → 19:30

These values are derived from the active calendar's seasonal model and the active scene's configured climate zone. The current in-game time (in decimal hours) is compared against them:

  • sunrise ≤ currentTime < sunset → light theme (day)
  • otherwise → dark theme (night)

The GM's client performs this check and (optionally) broadcasts the result to all connected players via Foundry's socket, so everyone's UI switches at the same moment.

Settings

Setting Scope Default Description
Transition Duration (ms) Client 1500 CSS crossfade speed. Set to 0 to disable.
Apply to All Players World true Socket-broadcast theme to all connected clients
Show Notifications Client false Show a brief UI popup when the theme switches

Fallback Behaviour

If Calendaria is not loaded (e.g. disabled for testing), the module falls back to updateWorldTime + a static 06:00 sunrise / 20:00 sunset. A console warning is shown.

Customising the Palette

The module adds dnt-day or dnt-night to <body>. All colours are CSS custom properties in styles/day-night-theme.css. Override any variable in your own world styles:

/* Make daytime backgrounds cooler/bluer */
body.dnt-day {
  --color-bg: #eef0f4;
}

Calendaria Climate Zones

Calendaria lets you assign a climate zone to each scene (Arctic, Temperate, Desert, Tropical, etc.). The zone affects the sunrise/sunset calculation — arctic summers have very short nights, desert campaigns near the equator have consistent 12-hour days, etc.

Configure zones in Scene Configuration → Calendaria tab within Calendaria's settings.

Troubleshooting

Players don't switch theme.
→ Make sure Apply to All Players is on, and the GM's Foundry tab is open.

Theme never changes despite time advancing.
→ Confirm Calendaria is active and CALENDARIA.api is accessible in the browser console.
→ Check that the scene has a climate zone configured in Calendaria if you expect seasonal variation.

CSS conflicts with another theme module.
→ Increase selector specificity in day-night-theme.css, e.g. body.dnt-night.dnt-night { … }.

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