[Solved] Need help with LOD generation on xbuf models

Ali_RS · August 28, 2016, 11:08am

Hi

I tried to generate lod on a model imported with xbuf. but it did not generate.(tried both in SDK and code). it generate OK if i import it directly from .blend —> .j3o

So i decided to generate LOD in blender using “Decimate” modifier.
I generated two LODs then imported them along with my main model to JME.
And set them using mainGeometry.getMesh().setLodLevels(vertexBuffer);

but the result is strange :

here is main model with lod_0 (model’s original index buffer)

wit lod_1

with lod_2

here is how it looks like in blender

here is code :

public static Node loadModel(ModelKey key, AssetManager assetmgr) {

        Node model = (Node) assetmgr.loadModel(key);
       
        if(model.getChild("LOD") != null){
            System.out.println("found LOD");
            
            //This is the node i have all lods for my model loaded from blender
            Node modelLODsNode=(Node) model.getChild("LOD");
            modelLODsNode.removeFromParent();
            
            SceneGraphVisitor visitor = new SceneGraphVisitor() {
                @Override
                public void visit(Spatial spatial) {
                    if (spatial instanceof Geometry) {
                        Geometry geometry=(Geometry) spatial;
                       
                        //Create an array of buffer to save LODs
                        VertexBuffer vbuf[]=new VertexBuffer[3]; //mode has 2 lods with it's main mesh
                        //vbuf[0] keeps model's main index buffer
                        vbuf[0]=geometry.getMesh().getBuffer(VertexBuffer.Type.Index);
                        for(int i=1;i<3;i++){
                            //Getting lod levels from modelLODsNode
                            Spatial lod= modelLODsNode.getChild(geometry.getParent().getName()+"lod"+i);
                            if(lod!=null){
                                Geometry lodMesh=(Geometry) ((Node)lod).getChild(0);
                                //Getting lod index buffer
                                vbuf[i]=(lodMesh.getMesh().getBuffer(VertexBuffer.Type.Index));
                                System.out.println("set lod level"+i+"to: "+spatial.getName());
                            }
                           
                        }
                        //setting lods to main geometry 
                        geometry.getMesh().setLodLevels(vbuf);
                       
                        geometry.setLodLevel(1);
                        geometry.updateModelBound();
                        geometry.getMesh().updateCounts();
                        

                    }
                }
            };
            
            model.depthFirstTraversal(visitor);
        }
    
      
        return model;
    }

Model download link :
https://drive.google.com/open?id=0B35eWZpi0dBoNlVwZjA3S21rOVE

Can you please help

Ali_RS · August 28, 2016, 5:01pm

To make it simple, I tested it on a simple sphere.
This time JME SDK could generate LOD but the same problem happens:

for sure something goes wrong with xbuf importer in the case of VertexBuffers.
So i decided to update the whole mesh instead of setting LodLevels.
So i changed this :

VertexBuffer vbuf[]=new VertexBuffer[3];
geometry.getMesh().setLodLevels(vbuf);

to this:

Mesh lodMeshes[]=new Mesh[3];
geometry.setMesh(lodMeshes[xx]);

And everything goes fine.
But i need to write my own LODControl then.

Domenic · August 28, 2016, 8:08pm

Is it possible to just copy the code from the “normal” LodControl to your own control and change those 2 lines?

Ali_RS · August 28, 2016, 8:24pm

Yes, i think.
normal control calculate level based on how many pixels on the screen the spatial is taking up.[Javadoc] .
I created my simple and light control which select lod based on distance from camera.

nehon · August 29, 2016, 7:20am

Could be interesting to dump the data from the position and index buffer of the model imported with blender and the model imported with xbuf.

Ali_RS · August 30, 2016, 7:05am

here you are :

Quick info :

xbuf    Index Buffer State:VertexBuffer[fmt=UnsignedInt, type=Index, usage=Dynamic, elements=37827]
Xbuf    Position Buffer State:VertexBuffer[fmt=Float, type=Position, usage=Dynamic, elements=113481]

Blender Index Buffer State:VertexBuffer[fmt=UnsignedInt, type=Index, usage=Dynamic, elements=37827]
Blender Position Buffer State:VertexBuffer[fmt=Float, type=Position, usage=Static, elements=27282]

** Note to Position buffer “Usage” (one is Static the other is Dynamic)

Buffer data was too long to put here. I uploaded it here:
https://drive.google.com/open?id=0B35eWZpi0dBoRFVTcEFOcGVxZFU

Buffer data printed in one long row for better comparison. So you may turn off wrap text mode in your text editor.

https://atom.io/ opens it fine.*

Regards

nehon · August 30, 2016, 7:59am

Well…xbuf has almost 4 times the vertex number that’s really strange…
It’s just right after importing right?

@david_bernard_31 do you do some special operation on vertices?

Ali_RS · August 30, 2016, 8:03am

Yes, right after importing
first i converted both to .j3o then directly loaded j3o and got the above information.
if you want I can try directly load them without converting to .j3o

david_bernard_31 · August 30, 2016, 8:45am

tesselation is run on blender side before export (to only export triangle)
the exporter don’t de-duplicate vertices

Maybe a bug in xbuf, I’ll investigate (when back to home)

nehon · August 30, 2016, 9:04am

ok so the mesh is already triangulated… maybe the lod generator doesn’t like that…

Darkchaos · August 30, 2016, 9:07am

The Blender Importer also performs triangulation.
Maybe the Generator doesn’t like duplicated vertices, though.

Edit: Does the Engine even support other Geometries than Triangles?

david_bernard_31 · August 30, 2016, 6:49pm

I did a quick test (in the train) export the default blender cube:
blender: 8 vertex, 6 faces
import .blend: 12 triangles (6 quad faces x 2), 36 vertex (12 triangles x 3 vertex)
import .xbuf: 12 triangles (6 quad faces x 2), 24 vertex (8 vertex x 3 quad faces)

So I have the opposite result xbuf vertex < import .blend vertex. So I need to do more test (eg with the sphere/mesh provided by @Ali_RS)

Maybe the issue is caused by the a trick I used:
xbuf use the blender mesh tesselation (not triangulation), it generates mesh with triangles or quads, in the case of quad the xbuf exporter export the 4 vertices but it generate 2 triangles only via indexes:

# xbuf
1--2
|\ |
| \|
4--3

indexes: 1,2,3,1,3,4

# import blend (hypothesis)
1--2
5  |
|\ |
| \|
|  3
4--6

indexes: 1,2,3,5,6,4

nehon · August 31, 2016, 6:30am

mhhh you mean the blender loader splits all the quads? that seems very strange…
Also, from what you say, I would expect the opposite result with LOD… and with the number of vertices of the character model.