Face Orientation issue

[Matthias_S]

Hi,

When doing this exercise I went to rotate one of the faces. Looking into Blender it looked quite fine, so I just continued.
However when importing my shapes into Unreal Engine, I experienced the next issue: the top of the doorway was not showing. It took me a bit of time to figure out what was wrong and how to fix it.

In the end, within the “viewport overlays” menu, I added “face orientation” which showed that these faces were red instead of blue (the normals were turned). Then selected the faces which were red (in Edit mode) and still in Edit mode, went to Mesh → Normals → Flip. After this the faces were showing blue and when importing now in Unreal Engine it showed ok.

I hope this information can help others, if ever facing this issue.

[Medial]

Good job with finding it an resolving yourself!
This is called backface culling, and does exactly what you describe: dont show back of the face in renderer.
It works like this on Unity aswell, as a matter of fact Id be surprised to find any game engine that doesmt have that.

You can also switch it on im Blender, but it is not comfortable to work with this on.

Its always worth to check for normals (aka face orientation) as they can mess a lot of things.

[FedPete]

It’s normal in the 3D world to not to show backfaces, because basically in real world they can not be seen!. Like the inside of a box when it’s closed. Game engines do this by default to save calculation times. What not can be seen (rendered), doesn’t need to be calculated.

But Blender, a 3D design tool, does show it by default!

A. It helps the creator in the design process.
B. Blender used a sort of raytracing algorithm. Where light bounces from the backsides of objects (invisible to the viewer, but touched by light rays).