Press a button on your controller to startButtons start red and turn black first time they are pressed. Joysticks should read about 0% in the center and ±100% at the edge. In the ideal world all joystick axes should be zero when released, but even high quality joysticks will have 3-4% deviation from zero, and 10% is not unusual. Most games have a "dead zone" of around ±15% to compensate for this.
All xbox controllers (one/360, etc) are detected as being 360 by current webkit browsers (e.g. Chrome, Edge). Firefox just knows what API is being used (Xinput). Webkit (but not firefox) allows triggering the vibration feature; test this by holding down 4 or more buttons simultaneously.
This is designed to visualize a standard dual-joystick gamepad, but may fail for devices that don't look like that. If it doesn't work, try this simpler version.
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