Hi lovely people,
I have some confusion about how Fresnel works on two-sided materials. According to the document, "In UE4, the Fresnel Material Expression node calculates a falloff based on the dot product of the surface normal and the direction to the camera. " What surface normal does it use when calculating on a two-sided material?
Let’s say we have a sphere mesh and a two-sided material applied to it. My guess is that when the camera is outside the sphere it uses the surface normal on the front-face and when it goes in it uses the backface normal. However, it seems that even if the camera is inside it still uses the front-face. In the beginning, I thought it was because the backface normals were not actually there. I plugged a PixelNormal into the BaseColor and it turned out that the backface normal is properly generated. And Fresnel works as expected when I plug PixelNormal into the normal vector in Fresnel. So Fresnel seems to not be able to use the backface normal for calculation when NormalVector input is default.
Is it true or there is something misunderstanding on my side?