Bug 129214 [Field Assist] - Decorated Field attachments not centering images horizontally
DecoratedField is supposed to center decorations horizontally on each side. The current attachments are not doing so. Also consider whether grid would have been a better choice for internal implementation.
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/DecoratedField.java
hoverShell = new Shell(parent, SWT.NO_TRIM | SWT.ON_TOP
					| SWT.NO_FOCUS);
			hoverShell.setBackground(display
					.getSystemColor(SWT.COLOR_INFO_BACKGROUND));
			hoverShell.setForeground(display
					.getSystemColor(SWT.COLOR_INFO_FOREGROUND));
			hoverShell.addPaintListener(new PaintListener() {
				public void paintControl(PaintEvent pe) {
					pe.gc.drawString(text, hm, hm);
					if (!CARBON)
						pe.gc.drawPolygon(getPolygon(true));
				}
			});
			hoverShell.addMouseListener(new MouseAdapter() {
				public void mouseDown(MouseEvent e) {
					hideHover();
				}
			});
		}
		/*
		 * Compute a polygon that represents a hover with an arrow pointer. If
		 * border is true, compute the polygon inset by 1-pixel border. Consult
		 * the arrowOnLeft flag to determine which side the arrow is on.
		 */
		int[] getPolygon(boolean border) {
			Point e = getExtent();
			int b = border ? 1 : 0;
			if (arrowOnLeft)
				return new int[] { 0, 0, e.x - b, 0, e.x - b, e.y - b,
						hao + haw, e.y - b, hao + haw / 2, e.y + hah - b, hao,