Does Canvas detect split screen?

No. Window layout is a function of your operating system, not the browser. Canvas has no API to query the window manager and cannot tell whether its tab is full-screen, split alongside another app, or on a secondary monitor. What Canvas does detect is focus state — when its own tab gains or loses focus. So split-screen is invisible UNTIL you click the other window, at which point Canvas fires a page_blurred event.

Why can the browser see my window size but not other windows?

The browser knows about itself: window.innerWidth, window.outerHeight, window.screen.width, etc. These describe the browser's own dimensions. The browser cannot enumerate other apps or other browser windows; that information is held by the OS and never exposed to web pages.

Will resizing my window flag me?

Canvas does not log window-resize events. You can resize the quiz window freely. The only thing Canvas tracks at the window level is the focus/blur state — if dragging a window edge happens to move focus to another window, then that focus change is logged, but the resize itself is not.

What about a second monitor?

Same answer. Canvas cannot detect a second monitor is connected. Looking at the second monitor doesn't move focus, so Canvas records nothing. Clicking on the second monitor moves focus and fires a blur event — same mechanic as split-screen.

Does Canvas Track Split Screen? — Live Test (Free 2026)

Short answer: no — Canvas cannot detect that you have your screen split between Canvas and another window. But the moment you click on the other window, Canvas fires a focus event. So split-screen itself is invisible; interacting with the other half is not.

The live values below prove it. Resize this window. Drag it to a half-screen. Move it to a second monitor if you have one. Click another window. Watch what changes.

What the browser exposes about your window (live)

window.innerWidth × innerHeight

—

window.outerWidth × outerHeight

—

screen.width × screen.height

—

screen.availWidth × availHeight

—

document.visibilityState

—

document.hasFocus()

—

window.screenX, screenY

—

devicePixelRatio

—

All of these update live. They're what any webpage can see — Canvas included.

What this means for Canvas

✅ Canvas CAN see

That you exist (the page loaded)
Whether the Canvas tab is currently focused
Whether the Canvas tab is currently visible
The dimensions of the Canvas window
Your screen's total resolution
When focus changes (page_blurred / page_focused)

❌ Canvas CANNOT see

Other open windows or their contents
Which apps are running
Whether your window is half-screen, full-screen, or floating
Whether you have a second monitor
What's displayed alongside Canvas
Mouse movements outside the Canvas window

Try it yourself

Try each of these and watch the values above:

Resize this window. innerWidth changes. The focus state does not. Canvas wouldn't log anything.
Drag the window to half-screen (Windows: Win+◄; macOS: green button + tile left). innerWidth drops. Focus stays "focused" because you didn't click anything else. Canvas wouldn't log anything.
Click on another window or app. Focus drops to "blurred." Canvas would now log "Stopped viewing the Canvas quiz-taking page".
Hover your mouse onto a second monitor without clicking. If your OS uses "click to focus" (default on Windows/macOS), focus stays. Canvas sees nothing.

What other tools change this

Respondus LockDown Browser — replaces your browser with a locked version that blocks resizing, multi-window layouts, and screen sharing at the OS level. Different game entirely; if your exam requires it, the analysis here doesn't apply.
Honorlock / Proctorio — record your screen via WebRTC screen-capture (with your explicit permission). A human reviewer watching the playback would see split-screen, second monitors, the other app windows. Canvas alone cannot do this; only a proctoring extension can.
The Window Management API (experimental) — modern browsers expose richer multi-monitor info, but it requires a permission prompt and Canvas doesn't use it.

Split screen is safe. Clicking the other half isn't.

Privacy Guard makes clicks across split screens safe by intercepting the focus events Canvas would log. Read what you want on the other half, then click freely — without log entries.

Get Canvas Ninja

FAQ

Does Canvas log resize events?: No. Canvas does not track resize. Drag your window edge as much as you want.
What if I have two browser windows of Canvas open?: Each Canvas window has its own session. Switching focus between them fires blur/focus events on each — both windows independently log entries. If you're taking a quiz in window A and click into window B, window A logs "Stopped viewing."
Does looking at a second monitor count as a tab switch?: Only if focus moves. Pure visual attention — eyes on the second monitor — doesn't trigger anything. Clicking, scrolling, or typing on the second monitor moves focus and fires a blur event.
Does Window Management API change this?: Theoretically yes — it lets sites enumerate monitors with permission. In practice Canvas doesn't use it and isn't planning to. Even if they did, the permission prompt is conspicuous.

What the browser exposes about your window (live)

What this means for Canvas

✅ Canvas CAN see

❌ Canvas CANNOT see

Try it yourself

What other tools change this

Split screen is safe. Clicking the other half isn't.

FAQ

Related

Canvas Tracking Test (live)

What Can Canvas See?

Does Canvas Track Split Screen?

Can Canvas Detect Screen Sharing?