Hello

I'm trying to create a little animation, so my pipeline is :
xara (draw 2D shapes) > Moi (convert 2D shapes to 3D surface) > messiah (animation & render).

First I draw in Xara (I used it for years, so I work faster in Xara), I get a few forms , and export in AI format :




Then I import AI file in Moi and use planar tool to convert line to surfaces (and set style to red) and export in obj and lwo format.


Then I import "obj" files in Messiah, and I can see that some surfaces are hidden.


In fact, when I turn around I can see the missing surfaces


If I use lwo, I get this :



On the messiah forum, I've been told :
=====
Every face on a mesh has a normal, a vector that describes the face's direction. This normal is part of how the surface gets shaded. When an application shows you both sides of a mesh, it's basically extrapolating this normal for the back face from the front. However, there is only one normal for each face stored in the mesh and if, as you're constructing your mesh, this normal gets directed inwardly instead of outwardly, your mesh will likely disappear when you import it into Messiah. The answer is to go back into your modeler and use it to "flip" the normals of the object. This will make the in-side normals into outside normals and should fix your problem. You will also likely want to "unify" them to make sure they all face out or in and aren't split between the two. Most modelers will allow you to turn off backside facing in display as well, so that you can see which side of your mesh is actually there. However, to answer your question, Messiah doesn't choose what side to use at all. It uses the normals of your mesh. If you've messed them up in construction, Messiah just shows you what you've done.
=====


So my question is : can I choose normal direction when exporting surfaces meshs from Moi3D ?

Thanks for any help.

Menu Option Import/ Export Modo Normal Style? whithout certitude :)

And use Meshlab? Wings3D for inverse normal...

Hi PP,

I do not know a way to check the normal direction in MoI, but you can "Flip" the normal before export. So for what you are seeing, you can go back into MoI, select the planer objects who`s normals are reversed and then press the "tab" key and type "Flip". You could also set up a shortcut key for that command.

In the applications I use, they do render both sides of a plane(option is usually: show/hide backfaces), but if the software does not support that, maybe you would be better to add a thickness to the planer objects. After you have created the planes, select them and use "shell" and add a thickness of, for example, 0.01, which creates solids and you would then have the normals facing outward on all sides and save having to go back into MoI.


- Steve

Thanks for your answers.

Frenchy Pilou (PILOU) : I think that "modo" is the default option for vertex normal style for lwo export (but I tried with lightwave, and the result is the same).

steve (STEVE_HOME) : To "Flip" objects I need to know which one I need to flip, so I need to export first, then check which objets are hidden, then flip those objets, then export once again.
So I think I will add a thickness.

I've used cinema 4D to display normal, and now I'm now almost sure that my problem come from normals :

Hi PP,

Yes, the problem you are seeing will be the normals, but the normals in MoI are generated from the direction of the curves that are creating the surfaces. So your construction lines made in xara are what are actually causing the "problem"

Adding thickness is probably the best/easiest way to stop this problem.


- Steve

Hi PP, yeah the easiest method will be to make those surfaces into solids by extruding them by a small distance as Steve mentioned above.

When your object is a solid that encloses a volume, MoI will automatically set the normals to point towards the outside of that solid.

When you only have open surfaces in MoI that do not enclose a volume, there isn't really a good way for MoI to automatically decide which side of the object is meant to be the "outside" part, so with open surfaces it is possible for the normals to be pointing in either direction. Which direction it is will depend on things like whether you initially drew the initial curve in either a clockwise or counter-clockwise orientation.

Often times there is an option in rendering programs to do a "2-sided" rendering where it will display both sides of an object instead of just only the positive normal side. I'm not sure if Messiah has an option to do that, but if it does you would probably want to just set that option and then you would not need to worry about this issue - that's why for example when you imported into Cinema4D the objects with reverse normals are showing up in C4D, because it does not only display one side of the object. It's kind of easier to set this option when it is available.

If there is no method in Messiah to do 2-sided rendering or display then that makes it even more likely that you'll want to extrude your objects into solids so that they won't just disappear when your camera rotates around them in an animation or stuff like that.

Re: Modo/Lightwave option for vertex normals on LWO export - that actually controls something slightly different - the "vertex normals" of a mesh are used for shading and are normals that are attached at every vertex of the mesh. Those are in addition to the face normals that indicate which direction the entire polygon mesh face is facing.

- Michael

Michael,

While I understand the theory, MoI has a Flip command but no way of showing what has been flipped. It would be nice if the face colours could be varied depending on which direction the normal is pointing. Then the issues can be sorted in MoI rather than have to export and come back to fix.

Hi Steve, yup a method for showing which side is the positive normal direction side is on my list of things to add to MoI.

- Michael

In Messiah, you can display both sides of an object instead of just only the positive normal side.

To do so, I select "render" tab, then "surface" tab, then clic on "defaut" under object name. And then I can see under the surface tab, another surface tab, with "double sided" option.

But instead, I will flip hidden objects, in messiah. It take not so much time and it will render more quickly.

"Display normals" would be a good feature to add to Moi.

Thanks everybody for taking time to help me.

> yup a method for showing which side is the positive normal direction side is on my list of things to add to MoI.

Ah good, this is something that I need too :)

Maybe a mode you can turn on where it shows with an arrow or line on each non-solid surface?

Hi NightCabbage,

> Maybe a mode you can turn on where it shows with an
> arrow or line on each non-solid surface?

Yeah either something like that or another possibility is to do it by color, with having the outwards facing stuff drawn in gray but reverse facing stuff drawn in some other color like red. That tends to make the reversed ones a bit easier to see immediately.

- Michael

< That tends to make the reversed ones a bit easier to see immediately.
Maybe yes :)