How The UVs Affect The Normals

This is very visible in Blender when viewing a mesh in Material Preview with a surrounding HDRI. The Smart UV Project has an option called “Rotation Method” that can affect how the normal map is behaving on the face(s). For this building mesh, I have one basic diffuse texture that use a normal map texture, making fake bevels. But since this material is using a normal map, it’s heavily affected by the UV rotation and the tangent space.

Some more information about this topic for this issue can be found here at blenderartists.org, especally what is pointed out by solo_GRV at https://blenderartists.org/t/why-does-uv-orientation-affect-normal-map-shading-2/1395223

For such flat building surfaces, I can make some variations in the shading and it still will be visible inside the GIANTS Engine.

A common mistake (human error) is to forget to change the color space. By default for normals, Blender is typically using the sRGB color space, while for normals it should be set to Non-Color.

This screenshot also fount at blenderartists.org, shows what’s going on:

Yes, the normal map should definitely point up since I used a color picker to get the value off the normal map node itself. The weirdest part is that if you unplug the flat image from the normal map node it looks just like it should, even though the image I feed to the node is literally the same exact color as the normal map node has on it by default.

https://blenderartists.org/t/why-does-uv-orientation-affect-normal-map-shading-trim-sheet-problem/1185586

Alternative Solutions

To correct some of these issues, one can select individual faces (usually one face) and rotate the UV. This is done by picking Face > Face Data > Rotate UVs (when in workspace Layout/Edit Mode).