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[Patheros]

In my project I have objects that are some times very far from the camera, and other times are very near. When they are close I want to render them as a Model, but when they are far away I want to render them as a billboard. Is there a way to achieve this effect with a single Universe and multiple views? It would be cool if I could achieve this with a Switch node that changes based on the view currently being rendered.

[Marvin Fröhlich]

In my project I have objects that are some times very far from the camera, and other times are very near. When they are close I want to render them as a Model, but when they are far away I want to render them as a billboard. Is there a way to achieve this effect with a single Universe and multiple views? It would be cool if I could achieve this with a Switch node that changes based on the view currently being rendered.

This is a technique called LOD (level of detail). A model is rendered in different complexities when it is nearer or farer to the camera. And it is also imaginable, that the farest LOD contains just a billboard.

I don't know, if we already have this in Xith. I didn't find it anywhere but in some model loader implementations. I anyway wanted to implement such a technique in the core. It should not be very difficult. So if not anybody tells me, that it already exists, I would advise you to wait some days and it will be awailable.

Marvin

[Mathias 'cylab' Henze]

The Switch is already there: http://xith.org/javadoc/core/org/xith3d/scenegraph/Switch.html all you need is a scheduled operation, that checks the distance between the switch and the viewer and select the appropriate subgraph.

This is called discrete LOD contrary to continuous LOD, because the former just switches between different models while the latter continuously transform the models mesh to get the best triangle count.

[Marvin Fröhlich]

The Switch is already there: http://xith.org/javadoc/core/org/xith3d/scenegraph/Switch.html all you need is a scheduled operation, that checks the distance between the switch and the viewer and select the appropriate subgraph.

Of course the Switch is already there, and I would use it for built-in LOD support. But it would just be convenient, if I could do the following:

Code:

LODSwitch ls = new LODSwitch();

ls.addLODItem( new LODItem( node1, minDist1, maxDist1 ) );
ls.addLODItem( new LODItem( node2, minDist2, maxDist2 ) );
ls.addLODItem( new LODItem( node3, minDist2, maxDist3 ) );

So I will implement that.

Marvin

[hawkwind]

Whenever I see a billboard at the end its often pretty obviously different than a shape,  I would use a low poly count shape instead.

[Patheros]

Another idea I had is as follows.

I'm making a space environment centered around a planet. Most of the time you will be close enough to the planet that I just render it right there. However if you get far enough away it gets cut off by the far clipping distance. So rather than just decrease its level of detail, I'm thinking I could move it into the sky box and render it there appropriately.

[Marvin Fröhlich]

Another idea I had is as follows.

I'm making a space environment centered around a planet. Most of the time you will be close enough to the planet that I just render it right there. However if you get far enough away it gets cut off by the far clipping distance. So rather than just decrease its level of detail, I'm thinking I could move it into the sky box and render it there appropriately.

This is exactly, what the SkyBox is there for .

Marvin

[Patheros]

But it would just be convenient, if I could do the following:

Code:

LODSwitch ls = new LODSwitch();

ls.addLODItem( new LODItem( node1, minDist1, maxDist1 ) );
ls.addLODItem( new LODItem( node2, minDist2, maxDist2 ) );
ls.addLODItem( new LODItem( node3, minDist2, maxDist3 ) );

So I will implement that.

Marvin

Is this simplemented yet? And if so where is it?

[Patheros]

Another idea I had is as follows.

I'm making a space environment centered around a planet. Most of the time you will be close enough to the planet that I just render it right there. However if you get far enough away it gets cut off by the far clipping distance. So rather than just decrease its level of detail, I'm thinking I could move it into the sky box and render it there appropriately.

This is exactly, what the SkyBox is there for .

Marvin

The problem is it needs to move in the sky box. I allow the camera to view the planet from any side, so if above it, the planet needs to be in the bottom of the sky box, but as you move to the bottom of it the planet needs to move above you.

[Marvin Fröhlich]

Is this simplemented yet? And if so where is it?

Oh, sorry, I forgot. Had several other things to do. Please give me two or three days. OK?

The problem is it needs to move in the sky box. I allow the camera to view the planet from any side, so if above it, the planet needs to be in the bottom of the sky box, but as you move to the bottom of it the planet needs to move above you.

Hmm... The SkyBox is always fixed around the Camera. But it is not fixed in relative rotation. Did you test that, or is it just a theoretical thought? Please have a look at the SkyBoxTest in xith-tk (update SVN before!). It should demonstrate, what you want.

Marvin

[Patheros]

Oh, sorry, I forgot. Had several other things to do. Please give me two or three days. OK?

No problem at all.

Hmm... The SkyBox is always fixed around the Camera. But it is not fixed in relative rotation. Did you test that, or is it just a theoretical thought? Please have a look at the SkyBoxTest in xith-tk (update SVN before!). It should demonstrate, what you want.

I have looked at the SkyBoxTest and I'm actually using Background to put stars in the sky already.

I've been using the term SkyBox incorectly. I mean simply a Background node.

I want to render a sphere (the planet) on a Background node in such a way that it looks like you are able to fly around it and look at it from the other side.

[Marvin Fröhlich]

I have looked at the SkyBoxTest and I'm actually using Background to put stars in the sky already.

Well, I've just modified it in a way, that a sphere is rendered in the center. But I see, your problem is a different one.

I've been using the term SkyBox incorectly. I mean simply a Background node.

I want to render a sphere (the planet) on a Background node in such a way that it looks like you are able to fly around it and look at it from the other side.

Sorry, I don't understand you again. A Background Node cannot be flight around. That's why it is a Background Node, isn't it? If you want to fly around it, that you'll have to use a regular (far away) Node.

Maybe someone else has an idea?

Marvin

[Patheros]

A Background Node cannot be flight around. That's why it is a Background Node, isn't it? If you want to fly around it, that you'll have to use a regular (far away) Node.

Maybe someone else has an idea?

Marvin

My idea was to create the illusion of being close. Its a force perspective trick. If you close one eye and hold your hand up so your fingers appear to be holding a far away object, then move your head slowly from side to side, keeping your fingers virtually around the far away object you will see what I mean. It should look (a little) like your hand is far bigger than it is, and its at the distance of the far away object.

The whole reason I thought to do this was so I didn't have to have an enormously high far clipping distance. 95% of my objects won't be rendered at far distances, however a small percentage (like the planet) will be. Presumably the shorter the far clipping distance is the better performance is. No?

[Marvin Fröhlich]

Presumably the shorter the far clipping distance is the better performance is. No?

I don't think so. The nearer the far clipping plane, the better is depth buffer precision. But I will test the performance impact of that.

Marvin

[horati]

I definitely see your point that 1000s of objects between you and the drawn planet would benefit from a short clipping distance; however, you still want super large but super far away objects to appear.

Can't you achieve your goal by using an additional render pass?  You could draw the planet in its own (probably display list?) scenegraph rendered behind the primary scene graph with the short clipping distance you desire.