Map a pointer-event coordinate (in the canvas overlay's local pixel
space) into normalised 0..1 source-content space. Coordinates outside
the content rect are clamped — keeps strokes inside the visible
video, which is the intended behaviour even when a user keeps
dragging into the letterbox bands.
Map a pointer-event coordinate (in the canvas overlay's local pixel space) into normalised 0..1 source-content space. Coordinates outside the content rect are clamped — keeps strokes inside the visible video, which is the intended behaviour even when a user keeps dragging into the letterbox bands.