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[Fwd: Re: [JAVA2D] Proposal for compound Composites]

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"Jan Bösenberg (INCORS GmbH)"

Hi Scott,

sorry for the late reply. I spent a few days in Bulgaria with my family
and needed some time to catch up to recent events (I did not expect the
ComboBox bug to generate that much noise, but it looks like you guys
found the best solution possible).

Other than Chris, after thinking again about my initial idea, I do not
think that CompoundComposite will ever work the way I thought it would,
and I think we should simply forget about this idea. I conducted some
tests and found that this is the wrong approach (but I still may be
wrong). On the other hand, the setAlpha() method with having the
RepaintManager handle the this through intermediate images seems to be a
great idea, since this is probably what people will be need in most of
the cases (you can expect a bunch of people trying to mimic some of the
Vista effects with Java at the beginning of 2007).

One important question that should be asked is in what way people will
use Composites in future, and if the setAlpha() method will in some way
comflict with these usages. For example, what if the developer decides
to set an alpha composite inside a paintComponent() method to paint an
icon translucently. Will this work as expected? If so (and I understood
from Chris' explanation that it will), the setAlpha() method is just
what I (and I suspect others as well) need.



P.S.: Chris, thanks for the extensive information, very interesting read.

Scott Violet wrote:

> Hi Jan,
> I wanted to get feedback from you on JComponent.setAlpha. Does Chris's
> explanation of how JComponent.setAlpha would work make sense? Is it
> what you are after?
> Thanks,
> -Scott
> ------------------------------------------------------------------------
> Subject:
> Re: [JAVA2D] Proposal for compound Composites
> From:
> Chris Campbell
> Date:
> Thu, 12 Oct 2006 00:01:30 -0700
> To:
> Jan Bösenberg (INCORS GmbH)
> To:
> Jan Bösenberg (INCORS GmbH)
> CC:
> Romain GUY , Richard Bair - Sun Microsystems -
> Santa Clara United States
> Hi Jan,
> This is an interesting proposal. It's also timely in that we've
> recently been discussing the possibility of adding a
> JComponent.setAlpha() (or similarly named method), and you touch upon
> some issues that came up in that discussion.
> Swing and Java2D developers have certainly run into this issue
> before, and our advice has typically been to use "intermediate
> images" [1] to achieve your effect. Using this approach, you can
> isolate parts of your rendering routine that might use a different
> composite or alpha value than other parts of your routine. Taking
> your example, you could make this work by doing the following:
> Composite myComposite = createMyComposite();
> Composite originalComposite = g2D.getComposite();
> BufferedImage img = ...;
> Graphics2D gimg = img.createGraphics();
> paintALot(gimg);
> gimg.dispose();
> g2D.setComposite(myComposite);
> g2D.drawImage(img, ...);
> g2D.setComposite(originalComposite);
> This works well most obviously in the SrcOver case (which I'd say is
> the 95% scenario), but it can work for other types of compositing as
> well. The downside of course is that it requires a lot of manual
> intervention on the part of the developer, and what if paintALot() is
> in some library that isn't under the developer's control? Before you
> know it, tin-hat paranoia takes hold and you're applying this
> technique all over your code, even when it's not necessary :)
> The SVG spec has something called "group opacity" [2], which is very
> similar to what I describe above, and probably very similar to the
> functionality that (I think) you're looking for. Here's a quote from
> section 14.5 of the SVG spec:
> "Object/group opacity can be thought of conceptually as a
> postprocessing
> operation. Conceptually, after the object/group is rendered into
> an RGBA
> offscreen image, the object/group opacity setting specifies how to
> blend
> the offscreen image into the current background."
> The SVG authors were going for that 95% scenario that I described
> earlier, in that the blending used is essentially SrcOver with a
> varying "opacity" value. Again, the nice thing here is that you can
> have lots of subelements within a group that each have different
> (individual) opacity settings, and then the "group opacity" setting
> is applied to that entire group (the conceptual image). This is the
> combination effect that (I believe) you are seeking.
> This also happens to be the approach that we're leaning towards if/
> when we implement JComponent.setAlpha(). The benefit here is that
> Swing's RepaintManager will essentially be doing all that dirty work
> that I showed earlier (with intermediate images behind the scenes as
> necessary). Going back to your original example, it should be as
> simple as calling label.setAlpha(0.5f), which will work equally well
> whether the content of the label is painted full opaque, or with
> translucent elements, as in your example. Either way, you'll get the
> results you're looking for, with minimal fuss. We'll need to specify
> this method, hopefully with pictures, so that developers understand
> what it really means to "set the opacity/alpha of a component", but
> right now we're aiming in this direction since it seems to solve the
> 95% case.
> As an aside, JXPanel today uses the naïve approach, and basically
> calls g.setComposite(SrcOver(alpha) at the top of its paint()
> method. This of course will work for the most simple scenarios, but
> it won't work for anything more complicated, like your example. You
> can achieve some "interesting" effects using JXPanel, most of which
> are incorrect, but anyway... :)
> Okay, so I'm rambling, and I haven't even gotten to your
> CompoundComposite proposal yet. I think that CompoundComposite could
> probably work as you describe, where the compose() methods are
> chained together, and you'd probably end up with the desired effect.
> My main concern with this approach is performance: we almost never
> use Composite.createContext() directly, but instead bypass it
> altogether with accelerated loops. If we had to fall back on
> createContext() and compose() for each operation, performance would
> suffer. I suppose we could find a way around this, maybe analyze the
> individual Composites within a CompoundComposite, and maybe collapse
> them if they're simple (like if you're trying to chain two SrcOver's
> together). Regardless, even if you could get all of this working and
> spec'd out properly, the conceptual model may be difficult for
> developers to understand. At least, it's not quite as
> straightforward as comp.setAlpha().
> Anyway, I hope that somewhere in here I've answered your questions
> sufficiently. I also hope that the setAlpha() method that's on the
> table for JDK 7 will solve the most common cases. Going forward, if
> we decide to add SVG and/or a "layers" API (for which Romain pines),
> it seems that both would fit in well conceptually with the "group
> opacity" and setAlpha() approaches. Thoughts?
> Thanks,
> Chris
> [1] Chet doesn't necessarily talk about the compositing issues here,
> but he does describe the general intermediate image approach:
> [2]
> masking.html#ObjectAndGroupOpacityProperties
> On Oct 6, 2006, at 6:19 AM, Jan Bösenberg (INCORS GmbH) wrote:
>> 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:
>> Composite myComposite = createMyComposite();
>> Composite originalComposite = g2D.getComposite();
>> g2D.setComposite(myComposite);
>> paintALot(g2D);
>> g2D.setComposite(originalComposite);
>> 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:
>> 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);
>> Since 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 very simple. What if its
>> createContext() method 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 of each of the simple 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 does what my
>> proposed CompoundComposite class would do.
>> Cheers,
>> Jan
>> ======================================================================
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