Interference pattern on overlapping meshes/facets

Questions
,
1

I have created two Meshes by adding triangular facets’ data. These meshes are initially in same plane and represent a sheet of paper. First mesh represents top side of the paper, and the second one represents the back side. I have set backculling true for both the meshes.

Now, these two messhes exactly overlap, but have opposite normals.

When I fold this paper by 180 degrees (let’s say mid-line) i see an interference pattern.
After the fold, stack ideally is like:

top-> back facets normal up -> front facets normal down-> front facets normal up -> back facets normal down

all these facets are in the same plan (overlap).

How do I resolve this interference pattern? Ideally, only backside should be visible now as there is not transparency.

2

Hi @vipaggar and welcome to the forum :slight_smile:

If you wan to render two faces of a plane, inverting the normal is not enough. Normals are used to compute lighting (basically) but not the face culling/visibility.

Check this article on Khronos site:
https://www.khronos.org/opengl/wiki/Face_Culling

So, I think the interference you see is zfighting. 2 faces are at the same position and depending on depth and float precision, you see pixel fragments from 1face or the other.
Once you have fixed the face winding, the interference should disappear.