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<h1 align=center>AWT Desktop Properties</h1>

The following refers to standard AWT desktop properties that
may be obtained via the
<a href="../Toolkit.html#getDesktopProperty(java.lang.String)">
<code>Toolkit.getDesktopProperty</code></a> method.
<p>
Each desktop property is named by a unique string, which
is the "name" of that property.
<p>
Desktop properties supported by the AWT but not documented
elsewhere - typically because there is no suitable
method or class - are documented here.
<p>
Desktop properties documented elsewhere are those which are
tightly coupled with a method or class which documents them.
<p>
Since desktop properties abstract an underlying platform
setting, they may not be available in environments that do
not support them. In the event that a desktop property is
unavailable for any reason, the implementation will return
<code>null</code>.
<p>
The following table summarizes the desktop properties documented
here, and their value types.
<p>
<table align="center" border="0" cellspacing="0" cellpadding="2" width="%95
  summary="Standard AWT Desktop Properties">
<tr bgcolor="#ccccff">
<th valign="TOP" align="LEFT">Property Name</th>
<th valign="TOP" align="LEFT">Value Type</th>
<th valign="TOP" align="LEFT">Summary Description</th>
</tr>
<tr>
<td valign="TOP"><A href=#awt.font.desktophints>awt.font.desktophints</A</td>
<td valign="TOP"><a href="../../util/Map.html">java.util.Map<a/></td>
<td valign="TOP">Font smoothing (text antialiasing) settings.<a/></td>
</tr>
</table>
<p>
<h2>Desktop Font Rendering Hints</h2>
<b>Desktop Property: <A name="awt.font.desktophints">"awt.font.desktophints"</A></b>
<p>
Modern desktops support various forms of text antialiasing (font smoothing).
<p>
These are applied by platform-specific heavyweight components.
However an application may want to render text using the same text
antialiasing on a drawing surface or lightweight (non-platform) component using
<a href="../Graphics2D.html"> <code>Graphics2D</code></a> methods.
This is particularly important when creating
<a href="../../../javax/swing/JComponent.html"> Swing components</a> which
are required to appear consistent with native desktop components or other
Swing components.
<p>
<h3>Basic Usage</h3>
The standard desktop property named
<b>"awt.font.desktophints"</b>
can be used to obtain the rendering hints that best match the desktop settings.

The return value is a
<a href="../../util/Map.html"> Map<a/> of
<a href="../RenderingHints.html"> <code>RenderingHints</code></a> which
can be directly applied to a <code>Graphics2D</code>.
<p>
It is a <code>Map</code> as more than one hint may be needed.
If non-null this can be directly applied to the <code>Graphics2D</code>.
<pre><code>
Toolkit tk = Toolkit.getDefaultToolkit();
Map map = (Map)(tk.getDesktopProperty("awt.font.desktophints"));
if (map != null) {
    graphics2D.addRenderingHints(map);
}
</code></pre>
<h3>Advanced Usage Tips</h3>
<p>
<h4>Listening for changes</h4>
<p>
An application can listen for changes in the property
using a <a href="../../beans/PropertyChangeListener.html">
<code>PropertyChangeListener</code></a> :
<pre><code>
tk.addPropertyChangeListener("awt.font.desktophints", pcl); 
</code></pre>
Listening for changes is recommended as users can, on rare occasions,
reconfigure a desktop environment whilst applications are running
in a way that may affect the selection of these hints, and furthermore
many desktop environments support dynamic reconfiguration of these
running applications to conform to the new settings.
<p>
There is no direct way to discover if dynamic reconfiguration
is expected of running applications but the default assumption
should be that it is expected, since most modern desktop environments
do provide this capability.
<h4>Text Measurement</h4>
<p>
Text always needs to be measured using the same
<a href="../font/FontRenderContext.html"> <code>FontRenderContext</code></a>
as used for rendering. The text anti-aliasing hint is a component of
the <code>FontRenderContext</code>.
A <a href="../FontMetrics.html"> <code>FontMetrics</code></a>
obtained from the <code>Graphics</code> object on which the hint
has been set will measure text appropriately.
This is not a unique requirement for clients that specify this hint
directly, since the value of the <code>FontRenderContext</code> should
never be assumed, so is discussed here principally as a reminder.
<h4>Saving and restoring Graphics State</h4>
<p>
Sometimes an application may need to apply these hints on a shared
Graphics only temporarily, restoring the previous values after they
have been applied to text rendering operations.
The following sample code shows one way to do this.
<pre><code>
/**
  * Get rendering hints from a Graphics instance.
  * "hintsToSave" is a Map of RenderingHint key-values.
  * For each hint key present in that map, the value of that
  * hint is obtained from the Graphics and stored as the value
  * for the key in savedHints.
  */
RenderingHints getRenderingHints(Graphics2D g2d,
                                  RenderingHints hintsToSave,
                                  RenderingHints savedHints) {
     if (savedHints == null) {
         savedHints = new RenderingHints(null);
     } else {
         savedHints.clear();
     }
     if (hintsToSave.size() == 0) {
         return savedHints;
     }
     /* RenderingHints.keySet() returns Set<Object> */
     for (Object o : hintsToSave.keySet()) {
         RenderingHints.Key key = (RenderingHints.Key)o;
         Object value = g2d.getRenderingHint(key);
         savedHints.put(key, value);
     }
     return savedHints;
}


Toolkit tk = Toolkit.getDefaultToolkit();
Map map = (Map)(tk.getDesktopProperty("awt.font.desktophints"));
Map oldHints;
if (map != null) {
     oldHints = getRenderingHints(graphic2D, map, null);
     graphics2D.addRenderingHints(map);
     ..
     graphics2D.addRenderingHints(oldHints);
}
</code></pre>

<h3>Details</h3>
<ul>
<li>The return value will always be null or a <code>Map</code>
<p>
<li>If the return value is null, then no desktop properties are available,
and dynamic updates will not be available. This is a typical behaviour if
the JDK does not recognise the desktop environment, or it is one which
has no such settings. The <b>Headless</b> toolkit is one such example.
Therefore it is important to test against null before using the map. 
<p>
<li>If non-null the value will be a <code>Map</code> of
<code>RenderingHints</code> such that every key is an instance of
<code>RenderingHints.Key</code> and the value is a legal value for that key.
<p>
<li>The map may contain the default value for a hint. This is
needed in the event there is a previously a non-default value for the hint
set on the <code>Graphics2D</code>. If the map did not contain
the default value, then <code>addRenderingHints(Map)</code> would leave
the previous hint which may not correspond to the desktop setting.
<p>
An application can use <code>setRenderingHints(Map)</code> to reinitialise
all hints, but this would affect unrelated hints too.
<p>
<li>A multi-screen desktop may support per-screen device settings in which
case the returned value is for the default screen of the desktop.
An application may want to use the settings for the screen on
which they will be applied.
The per-screen device hints may be obtained by per-device property names
which are constructed as the String concatenation
<pre><code>
"awt.font.desktophints" + "." + GraphicsDevice.getIDstring();
</code></pre>
<p>
An application can also listen for changes on these properties.
<p>
However this is an extremely unlikely configuration, so to help
ease of development, if only a single, desktop-wide setting is supported,
then querying each of these per-device settings will return null.
So to determine if there are per-device settings it is sufficient to
determine that there is a non-null return for any screen device using
the per-device property name.
</ul>
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