Classroom performance:
- WebSocket server (ws-server.js) for low-latency cursor & stroke preview
Replaces HTTP POST per event → eliminates per-message auth overhead
Session member cache (30s TTL) avoids SQLite query per WS message
Fallback to HTTP POST when WS not connected
- Cursor throttle reduced 100ms → 33ms (~30fps)
- Stroke preview throttle reduced 50ms → 20ms
- whiteboard.js: render() is now rAF-gated (_doRender/_rafPending)
Multiple render() calls within one frame collapse into one repaint
document.hidden check — zero CPU when tab is in background
visibilitychange listener restores canvas on tab focus
Guest board:
- guestClassroom.js route: public token-based read-only access
- guest-board.html: name entry + read-only whiteboard + SSE
- SSE: addGuestClient/removeGuestClient/emitToGuests
Screen share picker:
- Discord-style modal with tab switching (screen/window/tab)
- Live video preview before confirming share
- useExistingScreenStream() in ClassroomRTC
Fullscreen exit overlay:
- #cr-fs-exit-overlay button inside cr-board-wrap
- Visible only via CSS :fullscreen selector (touchpad users)
File sharing from library:
- Teacher picks file from library, sends as styled card in chat
- crDownloadLibraryFile() fetches with Bearer auth
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Minimap:
- Auto-shows in bottom-right corner when zoom > 1.05
- Renders full board content at scale (background + all strokes)
- Purple viewport indicator with darkened outer areas
- Click/drag to jump-pan the viewport
- Cleaned up on destroy()
Ruler/protractor property controls:
- Rotation handle (purple ↺) — drag to rotate around origin
- Resize handle (cyan ↔) — drag to change length/radius
- Protractor now supports rotation via ctx.rotate(ov.angle)
- Floating props panel in toolbar: angle° and length/radius inputs
- Panel auto-shows on first click/drag, hides when overlay toggled off
- Canvas-space hit testing with rotation-aware local coordinates
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Maxim Dolgolyov