Control movement

Your goal is to connect held keys to direction values, elapsed time and bounds.

Back up your current app. Copy keyboard Main and Mover into src/main/java/ using the switching steps. Run and click the canvas.

Before trying them, predict Main's direction values:

Held keys	horizontal	vertical
None	0	0
Left	-1	0
Right and Up	1	-1
Left and Right	0	0

Explain how separate if statements allow more than one held key to contribute. Run each case. Positive y moves down, so Up subtracts from vertical.

Main passes direction, elapsed seconds, width and height to Mover explicitly. Mover stores its own coordinates and uses:

x += horizontal * speed * seconds;

With speed 180 and seconds 0.05, Right moves 9 pixels on that update before the bounds check. Frame durations vary; do not assume that every frame takes 0.05. Moving diagonally updates both axes, so the original example moves faster overall on a diagonal than along one axis.

The circle's radius is 18. Its centre is limited from radius to width minus radius, and likewise for height. Limiting the centre to 0 would leave half the circle outside the canvas. Read Math.min as choosing the smaller value and Math.max as choosing the larger value.

1. Change speed from 180 to 90. Compare the movement without changing the time calculation.
2. Change radius from 18 to 28. Predict the allowed centre positions on the 640 × 400 canvas: x from 28 to 612, y from 28 to 372. Test all four edges.
3. In Main, change the right-key condition to accept either Right or D:

if (keyDown(KeyCode.RIGHT) || keyDown(KeyCode.D)) horizontal++;

Replace the original right-key statement with this one; do not add a second increment. Check D alone, Right alone and both together: all should produce the same rightward speed. Keep the other arrow controls.

Hold each direction against its edge: the whole circle should stay visible. Try opposite keys, diagonals, releasing all keys and changing window focus. Movement should stop on release or loss of focus; click the canvas before resuming.

Show one change and explain Main's input responsibility versus Mover's movement responsibility. Record an edge check and the D/Right/both comparison. Predict what would happen if Main stopped calling mover.update(...) but kept drawing it.