>Delivered-To: [EMAIL PROTECTED]
>MIME-Version: 1.0
>Date: Fri, 25 Jan 2002 12:29:44 -0500
>From: Mauricio Vives <[EMAIL PROTECTED]>
>Subject: [JAVA3D] Transparency and Ordered Groups
>To: [EMAIL PROTECTED]
>
>Kelvin and other interested readers,
>
>This message is in regards to Kelvin's response on Wednesday to Yuri about a
>problem we are having using basic transparency sorting and OrderedGroup
>nodes. By "basic" transparency sorting, I mean the default behavior of
>rendering transparent objects after opaque objects, a feature available even
>before Java 3D 1.3. You mentioned that any nodes under an OrderedGroup node
>will not be sorted; in effect, they will be rendered at random.
>
>Let me explain in greater detail what we are trying to do. We have a set of
>objects (BranchGroup1) that can be opaque and/or transparent. In addition,
>we have another set of objects (BranchGroup2) that we want to appear "on
>top" of all the other geometry. However, both BranchGroup1 and BranchGroup2
>can occupy the same 3D space. In order to achieve the desired effect, we
>need to do the following:
>
>1) Render BranchGroup1, with opaque objects first, then transparent objects
>with the depth buffer locked.
>(this is basic transparency sorting, which Java 3D provides)
>
>2) Render BranchGroup2, but with depth testing disabled.
>(this will make BranchGroup2 appear visible "through" any geometry in
>BranchGroup1, even if they occupy the same space)
>
>Thus, we need to use an OrderedGroup node to force BranchGroup1 to be
>rendered before BranchGroup2, but we also need basic transparency sorting
>for the children of BranchGroup1. However, as you mentioned in your
>response, no automatic sorting would be performed under BranchGroup1 because
>it resides under an OrderedGroup node.
>
>You also mentioned that we could simply perform our own sorting to separate
>transparent and opaque objects. Though this would be difficult, it can be
>done. However, if I understand you correctly, we would still not be able to
>take advantage of the "full" transparency sorting feature of Java 3D 1.3,
>and I don't think it would be reasonable for us to implement that feature
>ourselves (particularly since the Java 3D team has already done the work).
>
>I see no reason why Java 3D would not support the ability to do transparency
>sorting of the *grandchildren* of OrderedGroup nodes (or any other kind of
>sorting). Is there a reason why Java 3D can't do this? I would suggest
>this as a future Java 3D enhancement, if it is possible.
>
>Note that I agree that if there are transparent objects spread around the
>scene graph (under various OrderedGroup nodes), then even the enhancement I
>am suggesting would not lead to the proper transparency effect. However, as
>I explained above, with our application it would not matter.
>
>Kelvin, thanks for your help so far, and for any additional information you
>can give us.
>
>- Mauricio
>
You can try two things
(1) DecalGroup
(2) Turn on View setTransparencySortingPolicy for full scene
transparency depth sorting provided in v1.3 beta1.
Thanks.
- Kelvin
--------------
Java 3D Team
Sun Microsystems Inc.
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