# how to define the norms of the polygons in geometry

(GhPGame) #1

Hi,

I need more explanation on how the double sided polygons work in FMOD geometry.
Let’s say there is a room, there are sources inside and outside of the room. In order to define the norms of the quads of the cube (simulating the room) I need to know how the ray is emitting from the source and the listener.
I need to know how I should consider the norms of the quads (whether to define the vertices anti clockwise or clockwise), and how does it change if we define the polygons to be double sided or single sided.
To be more accurate, I want to know how to define the norms in a way that when we’re outside the room we don’t hear anything from the inside, and when we’re inside we don’t hear anything from outside (I set the direct occlusion factor to be 1).
Thank you.

(Brett Paterson) #2

Hi,
That is odd that this detail is not in the documentation (i’ll have to fix it) but yes the polygons must be in order at least to produce the correct normal for front/back. Clockwise should mean it points towards you but of course this depends on which plane we’re talking about.

You would flip the order and make it anti-clock wise to change the direction the occlusion happens from.

(GhPGame) #3

Thanks Brett. But once I define the vertices in a clockwise order and set double sided flag, FMOD considers both inwards and outwards normals, right?

(Brett Paterson) #4

Hi, if it is doublesided then the normals dont really matter any more, just the consistency of the winding (ie in order). I think technically it checks against 2 normals yes.

(GhPGame) #5

Great, thanks