Swing Hacks

Anti-Aliased Text Without Code #54

Chapter 7, Text

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283

HACK

H A C K

#54

Anti-Aliased Text Without Code

Hack #54

Draw anti-aliased text without any code changes at all using two clever tricks

introduced in Java 5.0.

Since Java 1.2, UI programmers can draw anti-aliased text. Unfortunately,

anti-aliasing must be enabled for every Swing component by writing a few

lines of code for each of them

[Hack #53]. This hack describes a clever way to

turn on anti-aliasing for an entire frame by adding a customized repaint

manager. As every programmer seeks for effortless solutions, we will dis-

cover how to do the same without writing any lines of code.

The Java 5.0 Trick

Sun Microsystems released Java 5.0, a.k.a. Tiger, in September 2004.

Among many improvements, like a new theme for the Metal L&F, this

release of J2SE paves the way for application-wide text anti-aliasing support

in Mustang, the upcoming release of Java. To this end, the Swing team

added a special field in the hidden class

com.sun.java.swing.SwingUtilities2.

Meant for internal purposes only, this class is left undocumented by Sun’s

engineering teams.

If you look closely at its source code, provided in src.zip with Sun’s JVM,

you’ll discover a very interesting method:

drawTextAntialiased(JComponent c).

This method returns a

boolean value used by Swing’s painting framework to

know whether the specified component must be drawn with anti-aliased

text. Here is its complete source code:

private static boolean drawTextAntialiased(JComponent c) {

if (!AA_TEXT_DEFINED) {

if (c != null) {

return ((Boolean)c.getClientProperty(

AA_TEXT_PROPERTY_KEY)).booleanValue( );

}

return false;

}

return AA_TEXT;

}

As you can see, there are two ways to enable anti-aliased text. In the first

case, the static variable

AA_TEXT_DEFINED is set to false, and a check is per-

formed against the component’s properties. Hence, a component in which

the property

AA_TEXT_PROPERTY_KEY is set to true will be anti-aliased. You can

set this property to a given component with the following line of code:

myComponent.putClientProperty(SwingUtilities2.AA_TEXT_PROPERTY_KEY,

new Boolean(true));

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Chapter 7, Text

#54 Anti-Aliased Text Without Code

HACK

Add this line of code in any of your applications, compile it, and launch it

with J2SE 5.0 and you’ll see the magic happen. While extremely useful, this

trick is not enough since we sure don’t want to do that for every component

instance in our UI. The source code of

drawTextAntialiased( )

gives us a

clue to understand how to globally enable anti-aliased text. When

AA_TEXT_

DEFINED

is set to true, the value

AA_TEXT

is returned. Both are defined at the

beginning of SwingUtilities2.java:

static {

fontCache = new LSBCacheEntry[CACHE_SIZE];

Object aa = java.security.AccessController.doPrivileged(

new GetPropertyAction("swing.aatext"));

AA_TEXT_DEFINED = (aa != null);

AA_TEXT = "true".equals(aa);

AA_FRC = new FontRenderContext(null, true, false);

}

The variables we are interested in are computed according to the value of the

object

aa. This object is the value of a JVM property called swing.aatext,

and it is supposed to be a

String object. AA_TEXT_PROPERTY_KEY is true only

when this property has been set, and

AA_TEXT is true when the value of the

property is the

String value "true". Given this information, we just need to

set the

swing.aatext property of the JVM to enable anti-aliasing. This can be

done on the command line with the help of the –

D switch, as in this example:

java –Dswing.aatext=true WebHunter

Figure 7-20 is what an application looks like with swing.aatext properly set.

I have also shown a screenshot of the same application without this prop-

erty for comparison (in Figure 7-21).

This trick is very useful and extremely simple to set up. Best of all, it

requires no change in the source code of the application, allowing use of it

even with applications you did not write. Unfortunately, this hack has two

major drawbacks. First, it works only with Sun’s J2SE 5.0 and is not guaran-

teed to be available with other vendors’ implementations. Also, remember

Figure 7-20. Anti-aliased text with J2SE 5.0 swing.aatext property