anti-aliasing : Java Glossary

2008-02-05 by Roedy Green ©1996-2008 Canadian Mind Products
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anti-aliasing

A technique of making fonts look smoother on screen by using blended colours in the pixels around the edges of letters. It fools the eye into thinking that the edges are sharper than they really are.

You can get W2K/XP to anti-alias with Start ⇒ Control Panel ⇒ Display ⇒ Effects ⇒ Smooth edges of screenfonts. You can get Vista to anti-alias with Start ⇒ Control Panel ⇒ System and Maintenance ⇒ Performance Information and Tools ⇒ Adjust Visual Effects (on left) ⇒ smooth edges of screen fonts.

. You can get Vista to anti-alias with Start ⇒ Control Panel ⇒ System and Maintenance ⇒ Performance Information and Tools ⇒ Adjust Visual Effects (on left) ⇒ smooth edges of screen fonts.

With an LCD monitor, you want subpixel anti-aliasing called ClearType. To turn it on click Start ⇒ Control Panel ⇒ Appearance and Personalization ⇒ Personalization ⇒ Windows color and appearance ⇒ Open classic colour and appearance ⇒ Effects ⇒ ClearType.

Without anti-aliasing, you will see jagged diagonal lines especially in the large sizes of spidery fonts with thin diagonal lines (e.g. e.g. Bodoni, Book Antiqua, Garamond, Serif and Zapf Calligraphic) especially on the capital W. Sun, even when anti-aliasing, pays no attention to the font rendering hints. This why small font sizes are so grungy looking. Anti-aliasing is primarily to make large font sizes look better.

Appearance	In JDK 1.6
In JDK 1.2	Anti-aliasing Gotchas
In JDK 1.3	Links
In JDK 1.5

What Does Anti-aliasing Look Like?

You can compare the same fonts anti-aliased and plain using the FontShower for Swing amanuensis which will display fonts in various sizes and colours with and without anti-aliasing and in the FontShower for AWT Applet in canvas mode. You are certain to see fonts without anti-aliasing in the FontShower for AWT Applet in canvas mode under W95/W98/Me/NT/W2K. You are certain to see anti-aliasing in the FontShower for Swing under XP/W2K3/Vista. The font where the differences are most obvious is DPCustomMono2.

Without anti-alias	Anti-aliased

The further back you stand, the more the samples look alike. Anti-aliasing is a similar sort of blurring that ironically creates the illusion of sharpness.

Several influences combine to decide whether you will get anti-aliasing:

Whether your OS/Windowing system supports anti-aliasing.
Whether you have anti-aliasing turn on system wide.
Whether your browser is turnning on anti-aliasing.
Whether the program is turning on anti-aliasing.
Whether the font supports anti-aliasing.
Whether your text contains unusual characters. Some will turn off anti-aliasing.

Anti-aliasing in JDK 1.2

To anti-alias fonts in AWT, you have to go through a gambit like this in your Canvas paint method:

There is another technique that uses an undocumented Sun class.

It won’t do you any good to override the paint method of a peered Component such as Label, TextField or TextArea since the rendering is handled by the peer. Whether they are anti-aliased is determined by the OS Control Panel.

Anti-aliasing in JDK 1.3

Anti-aliasing in Swing is similar to AWT, except that you override paintComponent instead of paint.

Smooth Metal LAF adds anti-aliasing to various Sun LAFs.

WrapLF is a LAF that lets you insert your own code.

Anti-aliasing in JDK 1.5

In JDK 1.5 you don’t have to override paint methods.

// Making a JTextArea use anti-Alias fonts
// only works in JDK 1.5+
jtextArea.putClientProperty(
                           com.sun.java.swing.SwingUtilities2.AA_TEXT_PROPERTY_KEY,
                           Boolean.TRUE );

Since JDK 1.5, it is possible to set the system property globally with swing.aatext=true. You can do that with java.exe -Dswing.aatext=true on the command line. Unfortunately the results are not always desirable. Sometimes small fonts look worse anti-aliased.

Anti-aliasing in JDK 1.6

The Java 1.6, has yet another anti-aliasing scheme, one that allows sub-pixel anti-aliasing that takes advantage of the geometry of the tiny red, green and blue phosphor dots on a CRT, or the equivalent dots on an LCD panel, that make up each pixel. Microsoft uses a scheme like this in Vista they call ClearType. In JDK 1.6 there is a system property called awt.useSystemAAFontSettings you can use to control anti-aliasing. Possible values include:

lcd
use ClearType style sub-pixel anti-aliasing.
false
no anti-aliasing. Fast with jaggies.
on
Gnome Best shapes/Best contrast. Not available in Windows.
gasp
Windows standard anti-aliasing.

In JDK 1.6+ there are also new values to use in setRenderingHints key and value, including VALUE_ANTIALIAS_OFF to turn anti-aliasing off.

Anti-aliasing Gotchas

Rendering character \u0e3f in a JTextArea inhibits antialiasing, ditto \ufdfc. \u0e3f is a Thai Baht currency sign like a capital B with a line through it. \ufdfc is the Yemeni Rial currency sign. It looks like Arabic script. Using one of these characters turns off anti-aliasing for the entire JTextArea. They seem to have no such effect in AWT with drawString or with TextArea. This strange behaviour has been observed both in Win2K and Linux.
I reported this to Sun and they explained the anomaly is a feature.
Internally when Swing sees a Thai or Arabic character, it switches to using a TextLayout for rendering. A TextLayout is created with a FontRenderContext, and the anti-aliasing Component of that FontRenderContext is applied when rendering too. In other words the usual anti-alias gambit does not work because it is anti-aliasing the wrong Component when you have Thai or Arabic characters.
Java 1.6 defaults its anti-aliasing to whatever the OS desktop setting is, making it behave like AWT peered components.

Learning More

Sun’s Javadoc on the RenderingHints class : available:

on the web at java.sun.com
in the current JDK 1.6.0_10 or in the old JDK 1.5.0_16 on your local Windows J: drive.

Sun’s JDK Technote Guide on anti-aliasing : available:

on the web at java.sun.com
in the current JDK 1.6.0_10 on your local Windows J: drive.

ClearType
fonts
FontShower for AWT: display fonts in various sizes and colours without and without anti-aliasing
FontShower for Swing: display fonts in various sizes and colours without and without anti-aliasing

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