Mirror command & flipped normals

[cheerioboy]

When using the mirror command with objects, the flipped object, if instanced, will have it's normals also flip.
What do people do to avoid this? Workarounds?

I've noticed that typically I don't catch this until later when I check 'backface cull' - and it doesn't really seem to matter in terms of vray rendering the objects. But now that I'm exploring importing my scenes into game engines, I'm seeing all the mess that I've made

The issue seems to resolve if I make the flipped object 'make unique'

But is there a way to maintain the objects as instanced, but not have the normals flip?

[Companioncube]

could use reference instead and put a xform on top of the mirrored object

[Vizioen]

When using the mirror command with objects, the flipped object, if instanced, will have it's normals also flip.
What do people do to avoid this? Workarounds?

I've noticed that typically I don't catch this until later when I check 'backface cull' - and it doesn't really seem to matter in terms of vray rendering the objects. But now that I'm exploring importing my scenes into game engines, I'm seeing all the mess that I've made

The issue seems to resolve if I make the flipped object 'make unique'

But is there a way to maintain the objects as instanced, but not have the normals flip?

This is an old 'bug' which unfortunately still exist. Basically 3dsmax mirrors an object by applying a negative scaling, which in turn flips the normals. There are a few workarounds, with xform or normal modifiers but the best one is to mirror an object using the mirror modifier instead of the mirror tool.

I had a lot of troubles in the day figuring this out because I used to import my models from sketchup and he did the same thing to mirrored imported objects although everything seemed fine in SketchUp.

There's a feature request on the autodesk website for a few years now but as usual we might wait a decade until this gets resolved: http://3dsmaxfeedback.autodesk.com/f...in-flipped-nor


You said that you don't experience vray giving you problems with it yet I found myself having trouble with refraction and dirt maps if I recall correctly, maybe other stuff too.

[cheerioboy]

Great tips, I'm going to try my hand with using References instead of Instances. And apply the xform modifier

thanks guys

[zoranm]

I use Symmetry instead of Mirror. It orients normals correctly. Of course, you still have to delete original object but it's still faster than re-orienting normal

[Vizioen]

I use Symmetry instead of Mirror. It orients normals correctly. Of course, you still have to delete original object but it's still faster than re-orienting normal

Why symmetry, mirror modifier works just as well without having to delete the original element. See attached screenshot. With Xview > Faces orientation you can see which ones are faulty. Mirror tool is in this case green and showing inverted normals.

[Da_elf]

i rememeber i had trouble with flipping a while back

http://forums.chaosgroup.com/showthr...with-mirroring

[cheerioboy]

i rememeber i had trouble with flipping a while back

http://forums.chaosgroup.com/showthr...with-mirroring

Hey, I am also using 2012 with the Nitrous display. I think several instances it is just a display issue, where when I remove the object as an instance, the normals flip back to normal without further modification. But the true test is when I export the mesh into Unity3d, and I see the issues with certain flipped geometry.

[DPS]

This isn't the case, it's a preview bug. I.e the dark red polys after mirroring make you think that they're flipped but they're not.

As far as I'm aware the only reliable way to check which way normals are facing is to convert to edit mesh and display normals.

So edit mesh is useful for something!

[alexyork]

You don't need to convert to edit mesh - just stick a fresh edit mesh on top of the stack.

It's a very very annoying max bug - you can select a flipped face, hit "flip" and it will not flip, visually or in reality. Stick a fresh edit mesh on top, do the exact same thing and suddenly it works. Very boring issue.