func (p *MyWidget) mouseReleaseEvent(e *ui.MouseEvent) {
p.line = append(p.line, e.Pos())
p.lines = append(p.lines, p.line)
p.line = []ui.Point{}
p.Update()
}
func (p *MyWidget) mouseMoveEvent(e *ui.MouseEvent) {
p.line = append(p.line, e.Pos())
p.Update()
}