Manually managing octrees

[fenomas]

Hi,

 

Considering a minecraft-style world, where "chunks" of static scenery are created and destroyed as the user moves around: 

 

Is it possible to manually manage the scene's octrees in order to keep picking fast? Notionally, I want to tell BJS: "Okay, I'm adding 50 meshes but they are all inside the following bounding box, so add a top-level octree and assume they're all in it."  And then later: "Ok, everything in the octree I added before is now gone."

 

Obviously I need to avoid processing the whole scene when doing this. Is this possible, or more broadly, is it the correct approach?

[GameMonetize]

You can easily pick an OctreeNode and add whatever you want inside. The Octree structure is pretty simple (I hope:))

[fenomas]

You can easily pick an OctreeNode and add whatever you want inside. The Octree structure is pretty simple (I hope:))

 

1. Do you mean OctreeBlock?

 

2. Are there any docs/code samples? From the API I can see vaguely what's going on but many details are unclear.

 

3. Once you construct an octree how do you tell the scene to use it? Only API I can find is the one for auto-creating one.

[GameMonetize]

1. Yes sorry

2. There is an usage doc here: http://doc.babylonjs.com/page.php?p=22561

3. If an octree is defined, the scene will automatically use it:

https://github.com/BabylonJS/Babylon.js/blob/master/Babylon/babylon.scene.ts#L1179

[fenomas]

Thanks for the replies 

 

As for docs, I meant are there any code samples involving manual creation of Octree or OctreeBlock instances - the docs only cover automatic creation.

 

For example, both classes take in a creationFunc parameter, but what is it meant to be doing?

[GameMonetize]

You're right this section need more doc

Here are examples of the creationFunc:

https://github.com/BabylonJS/Babylon.js/blob/master/Babylon/Culling/Octrees/babylon.octree.ts#L98

https://github.com/BabylonJS/Babylon.js/blob/master/Babylon/Culling/Octrees/babylon.octree.ts#L104

[fenomas]

Okay, by digging through the source I was able to get this working. For posterity, the code runs along these lines:

 

  // octree for whole scene

  var octree = new BABYLON.Octree()

  octree.blocks = []

  scene._selectionOctree = octree


  // branch block for area from 0..100, 0..100, 0..100

  var bmin = new BABYLON.Vector3(  0,   0,   0)

  var bmax = new BABYLON.Vector3(100, 100, 100)

  var branch = new BABYLON.OctreeBlock(bmin, bmax)

  branch.blocks = []

  octree.blocks.push(branch)


  // leaf block for area from 0..25, 0..25, 0..25

  var min = new BABYLON.Vector3( 0,  0,  0)

  var max = new BABYLON.Vector3(25, 25, 25)

  var leaf = new BABYLON.OctreeBlock(min, max)

  branch.blocks.push(leaf)


  // add meshes to leaf

  leaf.entries.push(myMesh)

 

DK: Having gotten it working, it didn't actually turn out to help performance like I'd thought...

But I'll ask you about that in a separate thread.

[GameMonetize]

feel free to add this to the documentation page if you will