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Here is the .blend file

enter image description here I'm fairly new to blender and am trying to model a low poly style car. I drew out the shape of the car by extruding and scaling planes. I selected groups of vertices between planes and pressed F to fill. This was working great until one of the faces was darker than all the rest. I went online to ask why and tried everything I found.

  • I selected all and recalculated normals. (The normal for the triangle is perpendicular to what it should be but I could not change it.).
  • I selected all vertices and merged by distance in case there were overlapping vertices.
  • I selected interior faces (there were none) and tried deleting.
  • I deleted all of the faces and vertices and rebuilt them to approximately the same place then filled again. Similar dark triangles appeared.

Car with face orientation and normals. I'm not sure how to caption these pictures. I'm sorry.

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  • $\begingroup$ Are there faces, with more than 4 vertices? These would be called N-Gons, and might cause some issues like that. Kinda hard to tell without a screenshot tho $\endgroup$
    – quest-12
    Commented Jun 9, 2022 at 10:46
  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented Jun 9, 2022 at 12:44
  • $\begingroup$ The thing where the normal isn't going where you expect it sounds very suspect to me. I would assume incorrect geometry that you somehow can't see as a result of that, and I think that is possibly the issue. $\endgroup$
    – Ben
    Commented Jun 9, 2022 at 13:43
  • $\begingroup$ Can you upload the blend file? $\endgroup$
    – Paul
    Commented Jun 9, 2022 at 19:43
  • $\begingroup$ Because of what Ben said I checked the coordinates of the troublesome vertices and it turns out they were just a hair off on the x axis, making that segment not perfectly flat like the rest. This caused the light to calculate weird. I copy pasted the correct x coordinate and it is fixed. Will upload blend file shortly. Thanks so much everyone!. $\endgroup$
    – Jay K
    Commented Jun 9, 2022 at 20:03

3 Answers 3

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Your object has its Z Scale set to $4.10339e-08$ or $0.0000000410339$. It transforms your geometry, introduces floating point inaccuracies and obscures the actual problem. Increasing the Scale back to 1 reveals the geometry is huge on Z axis. In particular, the Z coordinates of 4 vertices around building the 2 problematic triangles are:

  1. 22023472 m
  2. 22023460 m
  3. 22227340 m
  4. 22023472 m

Vertices 1. and 2. are on the same Z, vert 2. is 12 m away, and vert 3. is 200 km away. This is why the face normals seemingly are parallel to the faces - because scaling of those faces is so severe that their scaled versions of themselves become almost perfectly parallel to their original selves.

The solution is ⭾ Tab to go to Object Mode and ✲ CtrlA, S, to apply scale.

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    $\begingroup$ Thank you so much. That was such a technical, detailed answer. I have no idea how my geometry got so messed up. $\endgroup$
    – Jay K
    Commented Jun 10, 2022 at 9:56
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Have you tried selecting 1 vertex on the border of the dark polygon and moving it? Having used various 3d programs I have found when manually building an object via extrusions/filling/bridging (as opposed to deconstructing a solid sphere/cube primitive) you will encounter doubling issues whereby duplicate vertices/edges/faces are created. Sometimes the merge by distance doesn't work. By selecting one vertex only by clicking on it (not drag selecting) and trying to move it you will be able to confirm if no duplicates have been created.

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  • $\begingroup$ I grabbed and moved all connected vertices and there seems to be no duplicate vertices. $\endgroup$
    – Jay K
    Commented Jun 9, 2022 at 19:47
  • $\begingroup$ I've seen you've managed to resolve this. Your existing model I assume is static so clean edge loops don't apply so much. If you're modelling organic models such as characters especially if they're going to animate you have to take care not to model polygons in the way you have as any deforming areas will present problems like you've experienced. $\endgroup$
    – Helpme
    Commented Jun 10, 2022 at 17:05
  • $\begingroup$ Thanks for the advice! I'll be wary of that in the future :) $\endgroup$
    – Jay K
    Commented Jun 10, 2022 at 19:35
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The thing where the normal isn't going where you expect it sounds very suspect to me. I would assume incorrect geometry that you somehow can't see as a result of that, and I think that is possibly the issue. – Ben 6 hours ago

Because of what Ben said I checked the coordinates of the troublesome vertices and it turns out they were just a hair off on the x axis, making that segment not perfectly flat like the rest. This caused the light to calculate weird. I copy pasted the correct x coordinate and it is fixed. Will upload blend file shortly.

X coordinate of vertex is slightly off Corrected X coordinate, now normals are fixed and light is proper Thanks so much everyone!

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  • $\begingroup$ I have no idea how to mark a post as solved. $\endgroup$
    – Jay K
    Commented Jun 9, 2022 at 20:29
  • $\begingroup$ You may mark your answer as accepted after 48 hours. Read here for more information on self-answers. $\endgroup$
    – Timaroberts
    Commented Jun 9, 2022 at 20:43

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