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Very often I'll delete faces, simplify things a bit (dissolving unnecessary vertices) and make faces again by selecting vertices and using the "Make Edge/Face" tool F. Sometimes the generated faces are in the wrong direction, i.e. normals pointing inward, so I need to check and flip them manually.

My question is, how is the normal direction determined when making a face? It doesn't seem to depend on the direction/order of selecting vertices and the result is quite random.

Are there any tips to make face normals point at the desired direction so that I don't need to flip them manually later?

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If you create faces connecting to existing faces, they will be used to calculate the direction. Otherwise the direction is undefined at the moment.

If you have a file that you think is making faces pointing the wrong way, I'd be interested to know, however this is more of a bug report.

The possibility of making faces that point towards the view for example, or as you suggest, using the selection order is interesting and may be added but currently isn't supported.

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  • $\begingroup$ The reason I think it might relate to the selection order is because, at least in OpenGL, face culling is determined by the vertices order. Perhaps not the case in Blender then. Perhaps the times this happens to me is when there are no adjacent faces. $\endgroup$
    – Alvin Wong
    Commented Jun 14, 2013 at 4:13
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    $\begingroup$ In blender as with opengl the vertex order is used to define the face flipping, its just that the face creation function ignores the order you select vertices. If you think you find a case where blender could do better feel free to upload blend or report a bug. $\endgroup$
    – ideasman42
    Commented Jun 14, 2013 at 11:11

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