Swing Hacks

Add Translucence to Menus #12

Chapter 1, Basic JComponents

|

57

HACK

problem, you’ll need to develop a full repaint manager [Hack #53] that will force

Swing to always repaint the entire component tree, instead of just the menu

items. It’s a bit slower, but worth it if you really want this effect:

UIManager.put("MenuItemUI","CustomMenuItemUI");

RepaintManager.setCurrentManager(new FullRepaintManager( ));

One more bug is that the menu must fit within the frame. There are two

kinds of menus in Swing: heavyweight and lightweight. Lightweight menus

are normal Swing components. Heavyweight menus, on the other hand, are

drawn in their own top-level window. This means that there are two win-

dows being drawn: one for the real frame and one for the menu. If you use

heavyweight menus, the effect will stop completely because the windows

themselves can’t be transparent. Normally, Swing will use lightweight

menus, but if the menu has to be drawn outside of the frame—which can

happen if you have a small window or a really large menu—then it will

switch to heavyweight menus automatically and nothing can switch it back

until the application restarts. This means you should always make sure your

menus fit inside of your windows.

Future Ideas

This hack shows just one example of how you can completely change a

component’s behavior by customizing its Look and Feel class. Java2D gives

you the power to create a wide variety of graphical hacks. As an extension of

this technique, you could try blurring the components underneath the menu

or create a properly smoothed drop shadow.