Tutorial 10 :: Preparing for Object Culling, a Simple Octree

[mikeschuld]

Tut 10 discussion

[mikeschuld]

I am going to be updating the octree to simply use the static manager for everything instead of having a member object in the HMGame class. This makes things a bit easier to deal with later on (which you will see in the next tutorial that I am working on right now.) I'll update the original when I get it all sorted out.

[letsrock]

Please use PDF Files for your tutorial documentation again... 

[mikeschuld]

oops did i upload the wrong one? I'll go change it now

[Iarus]

I haven't done tut 11 yet, so I don't know if it was changed, but when you add objects and distribute them, you look at each child node and see if the object could be contained in it. Once the node is found, there is no use in testing the other nodes, so we can break the foreach loop

Code: ( HMOctnode )

private void DistributeObjects()
      {
         foreach(HMObject obj in myObjects)
         {
            foreach(HMOctnode node in myNodes)
            {
               if(node.Contains(obj.Position))
               {
                  node.AddObject(obj);
                  break;                                                        // <--------------
               }
            }
         }

         myObjects.Clear();
      }

I know your tutorials are not optimisation one, but design tutorials
I thought I would share

[mikeschuld]

Actually, the reason it keeps checking is just in case an object is on a boundary. This will allow us some special handling of boundary cases later on if we need to take advantage of them by making sure both nodes contain the object.

[Iarus]

ok

what happens if I create 5 objects really close to each other?
it'll split the node until all 5 objects are not in the same node anymore.
it can do lots of splitting.

what if (for some really stupid reason) all 5 are at the exact same position? StackOverflowException? [edit]I just tried it, and yup! stack overflow![/edit]
would implementing some kind of security for that case be useful? does that really happen often?
something like limiting the recursion to 10-20 levels or so.

Damn I've just finished tut 11! I'm starting 12, then... nothing 

---

I tried to add lots of teapots in my scene, and only a handful of them are there.
Do you have a clue why it happen?

Code:

private static void SetupScene()
{
    //Existing code

     System.Random r = new System.Random();
     int q = 0;
     HMModel m;

     for(q = 0; q < 1000; q++)
    {
        m = new HMModel(@"Content/Models/teapot");
        m.SetShader("BS");
        m.Position = new Vector3((float)(r.NextDouble()*200 - 100), (float)(r.NextDouble()*200 - 100), (float)(r.NextDouble()*200 - 100));
        game.Scene.AddObject(m);
        HMOctreeManager.OctRoot.AddObject(m);
    }
}

[edit]
OK never mind I'm stupid!
It's not r.NextDouble()*200 - 100, but r.NextDouble()*100 - 50
most of the object were not really added to the octree
[/edit]

[mikeschuld]

I actually updated my own code last night to only allow octnodes of a certain size or large, after that it just stops trying to split. This is only one of many solutions (probably a temporary one) for the problem

[Neil_Knight]

Does anyone have the tutorial PDF or ZIP files for any tutorials over 8?

I can't find them anywhere.

[mikeschuld]

The old tutorials do no work anymore. They were too complicated and the base engine was updated too much to allow for them to still function like they were and I have pulled them. The 8 on the blog list are the only ones currently used by myself and most others.

I still have the old pdfs of the deprecated tutorials if you would like to see them, but some of the renaming and refactoring may make them difficult to use. Let me know and I can email them to you.

[Neil_Knight]

Hi Mike,
I would love to see all of the old tutorials.  I'm really keen to see how you implemented your quad tree, so if you have tutorials 10 - 13 I be really interested in seeing these.

Also, are you going to convert Tutorial 8 to XNA 4?  I have been following your series and now I can't get the PostProcessing to work

[mikeschuld]

Working on the conversions still. They did some last minute changes to things in the RTM of 4 so I had to go through the refactoring all again. Working on it all at the same time as the book review so it will be a bit but hopefully not forever :p

[Neil_Knight]

Could you send me the old PDF files like you mentioned in your previous post?

I am hoping you still have 9-13

[Neil_Knight]

Hi Mike,
Just wondering if you have those old tutorial files?

[mikeschuld]

I found 9, 10, and 11 pdfs in the archives. Here's a zip containing them. These will not be directly compatible with the current base code in the engine so you may have to do some tweaking to get them functioning correctly. Good Luck!