Understanding OctTree

luckymutt · Post by **luckymutt** » Sat Jan 07, 2006 3:59 am

Just trying to understand a little better how the OctTree works.
The way it has been described is:

The OctTree optimizes the scene a little bit, trying to draw only geometry which is currently visible.

Presumably, this means that it doesn't need to bother with anything that is up/down/left/right of the screen.
What about geometry that is behind other objects?
For example, standing outside of a building that has a bunch of geometry inside that can't be seen, of the same mesh as well as other meshes, will the OctTree clip those until they fall into a line of sight?

disanti · Post by **disanti** » Sat Jan 07, 2006 5:04 am

Octree (not octtree) pretty much splits a mesh into 8 pieces, and if those pieces don't have less or equal amount of faces as the minimum, then it splits those pieces into another 8, etc.

Then it culls the pieces with the basic frustrum culling.
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krama757 · Post by **krama757** » Sat Jan 07, 2006 6:46 am

Also, there is octress reduction right? It reduces the number of triangles needed by drawing large triangles when you are far away and smaller ones when you are close.

luckymutt · Post by **luckymutt** » Sat Jan 07, 2006 6:38 pm

disanti wrote:Octree (not octtree).

I was getting my spelling from the API.
Is "Octree" the industry spelling?

When you say:

if those pieces don't have less or equal amount of faces as the minimum

What is the "minimum" here?
I'm kinda not getting it. (not that that matters, I guess...I 'd just like to better understand it...right now its just magic)

jam · Post by **jam** » Sat Jan 07, 2006 7:25 pm

Octtree definition

disanti · Post by **disanti** » Sun Jan 08, 2006 9:30 am

The minimum I'm talking about is the variable you input into Irrlicht when you create an octree scene node... the default is 128 polygons in Irrlicht.
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