public void scrollVertically(ScrollBar scrollBar) {
		if (image == null) return;
		if (imageHeight > visibleHeight) {
			final int oldOffset = displayFDC.yOffset;
			final int newOffset = Math.min(scrollBar.getSelection(), imageHeight - visibleHeight);
			if (oldOffset != newOffset) {
				paintCanvas.update();
				displayFDC.yOffset = newOffset;
				paintCanvas.scroll(0, Math.max(oldOffset - newOffset, 0), 0, Math.max(newOffset - oldOffset, 0),
					visibleWidth, visibleHeight, false);
			}
		}
	}