Transparency problems

[bohdan]

@Marvin Fröhlich

For the additional Shape3D flags: Just ask :).

Thanks Marvin!

@Yuri Vl. Gushchin

1. It is theoretically not possible to render mutually intersecting or self-intersecting shapes with standard OpenGL rendering modes.
2. The best one can do is to depth-sort geometry triangle-by-triangle, but it is too slow and even this does not guarantee correct result if some of triangles mutually intersect - you should cut trianges to smaller before sorting.
3. There are some combinations of alpha test, depth test and additive alpha blending that produce more or less good result, but in some angles they still do not work.

Alright… understand, that one I going to do going to assume transparent objects to be flat, which is mostly the case… and it should give much better results in general, especcialy if there is no intersection, though not always will be 100% correct…

@Yuri Vl. Gushchin

4. Most interesting. There are CORRECT TRANSPARENCY rendering techniques that can be implemented with modern cards and fragment shaders. At least one technique is called “Depth Peeling” which gives 100% correct result, but it is multipass (number of passes depend on the correctness required and degree of shape self-intersection).

Alright… yep, sounds very interesting!, haven’t heard of something like that exists… Great to know!

@Yuri Vl. Gushchin

OK, I will disclose one link that might be intersting for you: take a look at http://www.jproof.at/3d/. All examples there use Xith3D for the rendering. You should note that these examples are relatively old, and require JDK 1.4.2 (I think it will be installed on demand), so even don’t ask me to update them.

If you can run them (and I believe it is possible - some people from this forum confirmed they are running OK), check the House example, and take a closer look to the trees: they use 2-pass rendering with alpha test and render-to-depth-buffer, if I remember correctly. Also try to take out the house levels and you will see the transparency behavior when the level disappearing.

Thanks a lot for link and information! It was great to see, very nice done! Wokred fine, no problems. And transparencies handled surprisingly really nice there! It was good material to see how things can be possibly done!

[yvg]

Hi,

[quote]And transparencies handled surprisingly really nice there!
[/quote]
You can believe me - was a hell of work, and significant part of my contributions to Xith3D came that time when we at JProof made these apps.

Yuri

[bohdan]

@Yuri Vl. Gushchin

You can believe me - was a hell of work, and significant part of my contributions to Xith3D came that time when we at JProof made these apps.

Yes, I believe it was :), results are amasing…

Question to everybody… Can anybody ran Bleeding_Blending_test please? Same old version as it was before…
I get latest xith from CVS and experiencing odd behaviour of transparencies… Have difficulties to explain really :-, just need to get it working “normally” to test new sorting… please look at it and advice… something like color buffer is not cleared every frame + improper culling I guess as well, since top shape is freezing on revers go (like it is drawn once and that’s it)… anyhow very strange to me…

Bohdan.

Edit: and when I set shapes to be opaque - no animation is happenning at all ??? Like transform is not updated or something…

[Qudus]

@bohdan

Question to everybody… Can anybody ran Bleeding_Blending_test please? Same old version as it was before…
I get latest xith from CVS and experiencing odd behaviour of transparencies… Have difficulties to explain really :-, just need to get it working “normally” to test new sorting… please look at it and advice… something like color buffer is not cleared every frame + improper culling I guess as well, since top shape is freezing on revers go (like it is drawn once and that’s it)… anyhow very strange to me…

Edit: and when I set shapes to be opaque - no animation is happenning at all ??? Like transform is not updated or something…

Sorry, was my fault. Was easy to fix at last. Just setting the initial TransformGroupId to 1 instead of 0 :).

I also changed the test class to make it able to be run with LWJGL, which was not possible because of the Swing thing. I hope you’re not annoyed because of that.

Marvin

[bohdan]

@Marvin Fröhlich

Sorry, was my fault. Was easy to fix at last. Just setting the initial TransformGroupId to 1 instead of 0 :).

I also changed the test class to make it able to be run with LWJGL, which was not possible because of the Swing thing. I hope you’re not annoyed because of that.

Marvin

Thanks Marvin!
No problems ;D, going to check it out in a little while…