Why WebGL Interfaces Need an Interaction Budget, Not Just FPS

A WebGL scene can run at a stable 60fps and still fail its users if buttons feel unresponsive or the experience collapses after two minutes on a mid-range phone. This piece argues that frame rate alone is too narrow a metric for judging whether an immersive interface is production-ready.

Instead, it proposes an 'interaction budget': explicit limits across five dimensions — response (input acknowledgement speed), render (CPU/GPU cost per state), residency (memory across network, decoded assets and GPU), sustainability (behavior under heat, battery drain and long sessions), and equivalence (reduced-motion and non-3D fallbacks that preserve the same task).

Concrete guidance includes decoupling input feedback from animation completion, splitting render-loop work from lightweight input handlers, treating device pixel ratio as an adjustable quality lever rather than a fixed target, tracking assets by their decoded size rather than just transfer size, and testing for sustained rather than peak performance to catch thermal throttling.

For engineers building 3D product configurators, viewers or immersive web experiences, this reframes performance work around preserving the user's next decision under real device constraints — not maximizing visual fidelity in isolation.