Think with your hands.

The source stores each pointer coordinate divided by the canvas rectangle width or height and clamps each to zero through one. A horizontal coordinate one quarter across a four hundred pixel paper is one hundred pixels. The same normalized point on eight hundred pixels is two hundred. These bars compare display positions. Resizing redraws stored geometry instead of storing a new absolute screen position. PNG export makes a new white canvas twice the logical width and twice the logical height. A synthetic four hundred by three hundred paper becomes eight hundred by six hundred. Its pixel area is four times larger. These bars compare the two widths at half a pixel per source pixel. Export resolution is separate from the live drawing buffer, whose device pixel ratio is capped at three. If two completed strokes are cleared, the current list becomes empty but undo can restore both. These bars compare two strokes with zero after clearing. The source retains at most eighty undo snapshots, stores strokes locally and offers PNG download. Redo follows undo; drawing again clears redo history. Browser storage failure does not promise a saved draft, and exported image content remains the users own drawing.