[solved] addSphereSceneNode/polyCount and PrimitiveCount

[miko93]

Hello there,

I just noticed that when adding one debug sphere to my scene, the primitive count goes up more than I'd expected:

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gl_Data.pSceneManager->addSphereSceneNode(0.2f,16,0,-1,vPosition);

gives me an increase in primtive count of 512. Checking this with

Code: Select all

gl_Data.pVideoDriver->getPrimitiveCountDrawn()

Now, instead of 512, I'd expected to see an increase of 16 here, as the polyCount value given to addSphereSceneNode is 16. As far as I checked, my code is not executed more than once.

I understand I got the term "polyCount" wrong. What exactly does it stand for?

Thanks a lot for your help

[vitek]

The value 16 that you are passing to addSphereSceneNode() is not the total number of polys to use to make the sphere, it is the number of polys per row/column of the sphere.

Imagine you had a sphere with 16 rows and 16 columns and unwrapped it into a grid. The total number of cells in the grid would be 16 * 16 = 256. Now imagine that each cell of the grid is made of two triangles [primitives]. The total number of primitives for your sphere can would be (16 * 16) * 2 = 512. More generally, it would be (polyCount * polyCount) * 2.

Travis

[miko93]

vitek, thanks a lot.
I felt free to ask for adding this explanation to the irrlicht helpfile (over there in the bug reports forum).

miko