void scrollVertically(ScrollBar scrollBar) {
		if (image == null) return;
		Rectangle canvasBounds = imageCanvas.getClientArea();
		int width = Math.round(imageData.width * xscale);
		int height = Math.round(imageData.height * yscale);
		if (height > canvasBounds.height) {
			// Only scroll if the image is bigger than the canvas.
			int y = -scrollBar.getSelection();
			if (y + height < canvasBounds.height) {
				// Don't scroll past the end of the image.
				y = canvasBounds.height - height;
			}
			imageCanvas.scroll(ix, y, ix, iy, width, height, false);
			iy = y;
		}
	}