After I've joined 3 meshes into a single mesh with ctrl+j, part of it becomes transparent after I import it to Unity (see left side of the image). What could cause this and how can I fix it?
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3$\begingroup$ Looks like back-face culling to me, which would make sense if the normals of the bottom object were inverted. Try selecting everything in edit mode and pressing Ctrl N to recalculate the normals before exporting. $\endgroup$– gandalf3 ♦May 14, 2015 at 20:24
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$\begingroup$ Did you have any modifiers on the meshed before you joined them? $\endgroup$– DenisMay 14, 2015 at 23:47
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$\begingroup$ @gandalf3 It's strange, I had tried doing that earlier and it didn't work. Now after some more modifications to the model I rejoined the objects and found different parts to be transparent than before, and recalculating the normals fixed it this time. Thanks. $\endgroup$– mattboyMay 15, 2015 at 12:26
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$\begingroup$ @Denis Nope, no modifiers! $\endgroup$– mattboyMay 15, 2015 at 12:26
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1 Answer
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It looks like the normals of the bottom part are inverted, resulting in a transparent look due to back-face culling.
Try recalculating the normals with ⎈ CtrlN in edit mode (↹ Tab) with everything selected (A). Note that it's possible to create topology which cannot have consistent normals, which could be why this didn't work for you before.
answered May 16, 2015 at 5:38
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$\begingroup$ I've an object showing transparent faces (and black triangles), which I tried to fix after a Join. The object is not detected as non-manifold, normals are consistent and the problems are still present. $\endgroup$– minsDec 30, 2019 at 16:05
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$\begingroup$ @mins this is a wild guess, but is it possible you have a copy of your mesh overlapping in the same spot? $\endgroup$– gandalf3 ♦Dec 30, 2019 at 20:11
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$\begingroup$ Not the case. I found a bypass: Exporting the object (x3d) and reimporting it to create a clean mesh. $\endgroup$– minsDec 30, 2019 at 23:40
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1$\begingroup$ @mins glad you got it working, happy new year :) $\endgroup$– gandalf3 ♦Jan 1, 2020 at 12:28