This is just a thought that I had yesterday when I used the AlphaComposite
class, but I thought it may be worth sharing with you:
Setting a composite when painting on java.awt.Graphics2D object is usually done
like this:
[code]
Composite myComposite = createMyComposite();
Composite originalComposite = g2D.getComposite();
g2D.setComposite(myComposite);
paintALot(g2D);
g2D.setComposite(originalComposite);
[/code]
Just yesterday I decided that this will not work in some cases. Imagine you
want to create a fancy effect by making a translucent panel. To achieve this
you set an AlphaComposite.SrcOver with 0.5f alpha parameter in the panel's
paintComponent() method . On that panel you have a bunch of labels with html
text. You decided that if a label is disabled, it should be translucent, using
an AlphaComposite.SrcOver with 0.5f alpha. This works well on a normal panel,
but with our fancy translucent panel the disabled text will suddenly look
exactly the same as the enabled text (both will be translucent with alpha 0.5).
The reason is simply that the composites are replaced, while they should be
combined to get the desired effect.
If you look at Romain Guy's recent blog entries, you will see that using
Composites will be used more frequently, and sooner or later someone will run
into a problem similar to the one I described. The solution would be to have a
class CompoundComposite, that simply takes two Composite objects in the
constructor. The code from the beginning would then look like this:
[code]
Composite myComposite = createMyComposite();
Composite originalComposite = g2D.getComposite();
if (originalComposite != null) {
CompoundComposite compoundComposite = new CompoundComposite(originalComposite,
myComposite);
g2D.setComposite(compoundComposite);
} else {
g2D.setComposite(myComposite);
}
paintALot(g2D);
g2D.setComposite(originalComposite);
[/code]
I do not know too much about the inner workings of Java2D, but I would like to
know if it is possible at all to create a class that can combine two arbitrary
Composites. Maybe it is even very simple. What if the createContext() method of
such a class creates a CompundCompositeContext with a CompositeContext from
each of the simple Composites (created by calling the simple Composites'
createContext() method). The CompundCompositeContext's compose() method would
then call the compose() method on each of these CompositeContexts.
What do you think? Am I on the right track? And if so, should this always be
used when working with Composites? And if so, should CompoundComposite maybe be
added to the java.awt package?
Just for the record, a similar problem exists for the AffineTransform, but here
the concatenate() method in the AffineTransform class does what my proposed
CompoundComposite class would do.
Cheers,
Jan
P.S.: Sending messages to this forum through [EMAIL PROTECTED] does not seem to
work for me anymore (no error messages, no replies, message just never
arrives). I have to use the java.net web interface. Does anybody have an idea
how I can fix this?
[Message sent by forum member 'jansan' (jansan)]
http://forums.java.net/jive/thread.jspa?messageID=160667
===========================================================================
To unsubscribe, send email to [EMAIL PROTECTED] and include in the body
of the message "signoff JAVA2D-INTEREST". For general help, send email to
[EMAIL PROTECTED] and include in the body of the message "help".
