> Nothing makes it repaint.
Use MyPaintBox.Invalidate and make all your drawings your the
MyPaintBox.OnPaint event handler. You should never draw to a TPaintBox
from outside this event handler. If you need a control that "remembers"
previous drawings use a TImage with a TBitmap (at the cost of more
memory usage). Of course you can also use a TBitmap internally which you
paint to your TPaintBox.Canvas in its OnPaint event handler.