Weird shapes appearing on part in darkness

[Zyrac]

So, I'm making a habitat module thing, and I noticed a weird thing that happens when the part's in the dark. Some weird shadowy shape things appear on it that aren't visible in the VAB or when it gets light. Any idea what's going on? You can see them on the roof and window in the first image, and that they're gone in the second.

[SpannerMonkey(smce)]

Hi . that looks to me to be a problem with the models normals,  it looks very much like you have and edge running through that panel, so the resulting panels are not properly triangulated ,  rather than a diagonal edge running from corner to corner of that large segment, it would display much better if each of those visible window panels were re triangulated individually.  The how of that will very much depend on the modelling app you've used.

Or as a quick unity fix, that sometimes works for small errors, allow unity to calculate the normals,  be warned if you've carefully set up smoothing groups etc doing this can change the appearance quite dramatically

[Zyrac]

Well, I'm really at a loss.  I tried the Unity fix, but the issue persists. What I don't understand is where exactly the problem is occurring. This is the original mesh in Blender (as you can see, there are no edges running across the faces where the issues appear):

[Zyrac]

So, I believe I've found a fix. I experimented with extruding the window faces a little and it seems to have made the problem go away. I've still no idea what caused the problem in the first place or why extruding the faces fixed it, but I suppose all that matters is that it did. 

EDIT: Well, it certainly mitigated the problem slightly, but it's not fixed, and in some cases it didn't really make any difference at all. What's weird is that the problem seems to be created between Unity and KSP, since there don't seem to be any signs of it in Blender or in Unity scene view.

Edited April 22, 2018 by Zyrac

[Bonus Eventus]

My guess is blender is auto triangulating on export to fbx. Like @SpannerMonkey(smce) said, try pre triangulating the faces to control where the splits happen. Likely you have extra verts on some of your edges. Extruding the faces is probably unnecessary. You can also try applying unique smoothing groups to those faces so the normals aren’t average with the other polygons around the window frame. I always use smoothing groups myself.

[Shadowmage]

On 4/21/2018 at 8:55 PM, Zyrac said:

What's weird is that the problem seems to be created between Unity and KSP, since there don't seem to be any signs of it in Blender or in Unity scene view.

The artifacts you are seeing look to me like a known and long-standing issue with 3D rendering and some of the 'optimizations' taken to make shadows usable in real time.

Specifically, look at the Shadow Bias setting in the Unity documentation

https://docs.unity3d.com/Manual/ShadowOverview.html

(this isn't something you can fix in the model, it is a part of the rendering engine)