Extruding makes reversed normals. Align/flip normals does not fix issue. #39135
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Reference: blender/blender#39135
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System Information
I7 3630qm, 8GB RAM, 750M GT 2GB, Win 8.1 64
Blender Version
Broken: (example: 2.70 RC1
19f7f9a
)Worked: 2.69
Short description of error
Polys get wrong normals when extruded. There seems to be no exact order for this to happen. Sometimes it works fine. Sometimes is so bad that half of the polys are right half are wrong. Using align normals does not fix the issue. It seems to align them opposite of the camera view or object exterior so to speak. Other times it keeps some in one direction, others in opposite direction, just flips them around.
Exact steps for others to reproduce the error
Changed status to: 'Open'
Added subscriber: @00Ghz
Added subscriber: @mont29
I cannot find any issue with normals, following your given steps… Pleas attach a file demonstrating the issue.
Bug.blend1
Here.
Normals are reversed when they shouldn't be.
I do not see the problem… just flip them (after having selected the whole mesh, obviously), and issue is gone.
No you don't get it. This happens a lot in other extrusions as well. It is annoying to flip every time. And as I said sometimes it doesn't even work at all. Some normals stay inside, some outside in the same selection.
It is definitely a bug that never happened in 2.69
I’m sorry, but I tried extruding following your steps, and could not reproduce this… Normals are always consistent here, as far as I can tell… So what we need is a file just before the extrusion where we just have to extrude to reproduce the issue you describe.
Ok.
Let me provide the steps again because I missed something.
The file is the same I uploaded, you can use that. Also it is very important you stay in top view(or left,right etc but didn't test with those) at all times and follow steps exactly otherwise bug won't happen.
I followed exactly those steps in both 2.70 and 2.69, in the former at least both normals are in the same dir, in 2.69 I get opposed (mixed inwards/outwards) normals…
Anyway, I do not see a bug here, in that kind of operation there is no real way to chose a right normal, it merely depends from the order in which faces use vertices…
Assigning to Campbell to get its advice, just in case.
that might be the case, but yet again sometimes in the same object with more complex selection this thing causes some normals to be inwards some outwards. Using align or flip normals won't do any good since it just reverses each individual normal.
Let me give you an example. Let's say you got an Object with A, B, C, D, E as all connected polys and will be using 0 for inwards normal, and 1 for outwards normal
What happens sometimes that you get A,B,C, as 1 and D and E as 0. Let's now align normals as you suggested to fix the issue. Result? A,B,C = 0, D,E = 1
Obviously flip will just get back to original values.
Now as I see it this is a bug, not something that should be happening at all. What I should get is A,B,C,D,E = 0 or 1 . All of them, not some.
Ok. Another issue with normals and this time ain't from top view.
Although I am using the latest build from graphical.org
Anyway steps:
Added subscriber: @ignatz
I tried that last one with the circle within EDIT.
Depending on which direction along the Z-axis you extrude (positive or negative) you get a different direction of the normals, either all pointing in or else all pointing out.
Changed status from 'Open' to: 'Archived'
Added subscriber: @ideasman42
Talked with @ideasman42 about this one, he confirmed me it’s not a bug. Yes, a flat face has a normal in a direction. Yes, a flat face being non-closed volume (actually, not volume at all), it does not have an “inside” or an “outside”. Yes, when you extrude, normals of org selection are kept, which can lead to inwards normals in some cases…
This is not a bug, and not a regression. Thanks for the report, but will close it now.