The Multi-Window System

Why Mimir uses four separate windows and how they communicate.

The Problem

Running a D&D session with a digital tool presents a tension: the DM needs full control of maps, monsters, and notes — but players should only see what’s been revealed. A single window can’t serve both needs at once.

Four Windows, Four Roles

Mimir solves this with four distinct application windows, each built as a separate Vite entrypoint with its own HTML file and Vue app instance:

Main Window

The primary interface. Campaign management, character sheets, module prep, settings — everything you do outside of active play happens here. This is a full Vue Router application with navigation between campaigns, modules, characters, and reference materials.

DM Map Window

A dedicated map view for the DM during play sessions. Shows the full map with all tokens (including hidden ones), fog of war controls, and light source management. Opens as a separate window so the DM can position it on their screen while the player display runs on a projector or TV.

Player Display Window

What your players see. Shows only the revealed portions of the map — fog of war hides unexplored areas, hidden tokens are invisible, and the viewport is controlled by the DM. Designed for a second monitor, projector, or TV facing the players.

The player display has no interactive controls. Players can’t pan, zoom, or click on anything. The DM controls exactly what appears.

Sources Window

A standalone D&D 5e reference browser. Monster stat blocks, spell descriptions, item properties — all searchable and browsable. Opens as a separate window so you can keep reference material visible while working in the main window or running a session.

Why Separate Windows?

Independent Positioning

Each window can live on a different monitor. A typical two-monitor setup:

Monitor 1 (DM): Main window + DM Map Window side by side
Monitor 2 (Players): Player Display full-screen

Or with three monitors:

Monitor 1: Main window (prep, notes)
Monitor 2: DM Map Window (tactical view)
Monitor 3: Player Display (player-facing)

Isolation

Each window is a separate Vue application instance. A crash or heavy rendering in one window doesn’t affect the others. The player display stays smooth even while the DM is loading a complex map in another window.

Focused UI

The player display strips away everything players shouldn’t see — no toolbars, no sidebars, no token lists. The DM map view shows everything. Same data, different presentations.

Communication Between Windows

The windows share data through two mechanisms:

Shared Database

All windows read from the same SQLite database. When the DM places a token in the main window, it’s written to the database. When the DM map window loads, it reads the current state.

Tauri Events

Real-time synchronization uses Tauri’s event system. When the DM:

Reveals fog of war → the player display updates immediately
Moves a token → both map windows reflect the change
Changes the viewport → the player display pans to match
Toggles blackout → the player display goes dark instantly

Events are typed and scoped — the player display only receives events it needs to render, never internal DM state.

Theme Synchronization

When you change the application theme (light, dark, or hyper), a Tauri event broadcasts to all windows so they switch together. The DM map and player display default to dark theme regardless, since they’re typically used in dimly lit game rooms.

The Blackout Feature

A small but critical feature: the DM can instantly black out the player display with a single toggle. This is essential for:

Switching maps between encounters without spoiling the next area
Pausing to set up tokens before revealing a new room
“Theater of the mind” moments where you want players focused on narration, not the screen

Mimir - D&D Campaign Assistant