The on-screen circular input disc let both the mouse and the gamepad drive
the knob outside the visible circle.
- Gamepad: each stick axis was clamped to [0,1] independently, so a full
diagonal push reached the square corner. Clamp the stick *vector* to the
unit disc (radially symmetric) before mapping to [0,1]; covers both sticks.
- Mouse: the circular variant clamped in normalised [0,1]^2 but the canvas
drew the knob across the full non-square panel against the inscribed circle,
so the disc rendered as an ellipse that spilled past the rim. Map both the
pointer and every drawn position (knob/pins/markers/trail/flash) through the
inscribed-circle geometry, and disc-clamp the auto-drift.
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