final Scale scale = new Scale(shell, SWT.HORIZONTAL);
scale.setBounds(10, 570, 400, 80);
scale.setMaximum(255);
scale.setMinimum(50);
scale.setPageIncrement(10);
scale.addListener(SWT.Selection, new Listener() {
public void handleEvent(Event event) {
int perspectiveValue = scale.getMaximum() - scale.getSelection() + scale.getMinimum();
shell.setAlpha(perspectiveValue);
}
});