topic Re: Backfacing color in 3ds Max Forum

Backfacing color

markus — Thu, 21 Dec 2017 10:17:18 GMT

Hi. I have a model imported from another software (Keyshot via FBX). The model has a lot of flipped normals, however they render fine so it's not a problem. But it's annyoing that for some reason it will sometimes show the backfacing as black in the viewport (backface culling is off), somtimes not (if I change something in the material editor it seems to update and display correctly, but after starting a render it resets back to black again. I can't remember having this issiue in previous versions of max. Does anyone know a way to control it, a workaround or setting, anything? I don't want to spend time on manually flipping the normals on all the wrong surfaces, since it doesn't really matter for the final output, but it would be nice to have a better preview in the viewport!

Viewport will display flipped normals as black (sometimes, not always)

Re: Backfacing color

darawork — Thu, 21 Dec 2017 10:48:07 GMT

Hi,

I wonder if this MaxScript would help you?

https://forums.autodesk.com/t5/3ds-max-forum/toggle-quot-2-sided-quot-for-all-materials-of-selected-objects/td-p/6806846

The idea is to make all your scene materials double-sided, that way it won't matter as much if there are some normals flipped.

Btw, have you tried applying a Normal Modifier to all the scene entities? You can select all objects and apply one modifier to all at once.

Re: Backfacing color

markus — Thu, 21 Dec 2017 10:59:41 GMT

The script won't help, because the materials are already 2-sided materials (Vray materials). The thing is this only happens when I start interactive rendering in Vray (the viewport changes). I'm not sure why this happens and I would consider it as a bug/defect.

Adding a normal modifier doesn't solve anything. The meshes use explicit normals from Catia, and the normal modifier will destroy those. It also flips all, both correct and incorrect normals. The surfaces aren't welded so it can't "unify" anything either)

Re: Backfacing color

darawork — Thu, 21 Dec 2017 11:19:21 GMT

Ahh ok.

I presume you are aware that vRay RT doesn't have the same scope of material rendering capabilities as vRay ADV, that said do you notice anything that seems not supported in your scene from this list:

https://docs.chaosgroup.com/display/VRAY3MAX/V-Ray+RT+Supported+Features#V-RayRTSupportedFeatures-Materials

I stopped using vRay RT because I found it too restrictive in this regard.

Re: Backfacing color

markus — Thu, 21 Dec 2017 11:22:26 GMT

I'm not rendering in RT. Vray ADV has Interactive rendering since version 3.5 or something.

Re: Backfacing color

markus — Thu, 21 Dec 2017 11:24:59 GMT

As you can see the rendered surfaces look just fine:quick IPR preview from Vray Advanced 3.6.04

Re: Backfacing color

darawork — Thu, 21 Dec 2017 11:43:21 GMT

Ahh, I jumped ship at 3.4 (Sorry, unintentional pun) to move over to Corona.

Btw are you using a version 3DSMax post 2016? Because in my opinion that would account for the 'less-than-perfect' viewport display of materials/faces.

:edit: another thing to check would be the models distance from the world origin point 0,0,0

Re: Backfacing color

markus — Thu, 21 Dec 2017 11:46:23 GMT

hehe, I hear Corona is nice too, but I'm happy with Vray, most of the time anyway. The IPR rendering in Adv is one of my favorite features, although it has been prone to crash Max on occasion. I'm hoping this latest update (max 2018.4 and Vray 3.6.04 is going to be more stable, but I've only used it for a few days).

Anyways, its the absolute latest iterations of Max and Vray I'm using right now.

Re: Backfacing color

darawork — Thu, 21 Dec 2017 12:01:07 GMT

Yeah Corona is our preferred rendering engine of choice in the office now, and with the merger of Corona and Chaos earlier this year we are slowly getting the best of both worlds. We still use vRay (3.4) for revising older projects. Anyway the choice of rendering engine should not effect the viewport display too much.

In my brief foray into 3DSMax 2017 I found the viewport to be less than ideal in many situations, blackfacing being one of the constant annoyances encountered, along with materials burning too bright, and sunlight systems not working properly, etc...

I managed to reclaim some normality with the use of PowerPreview ( http://www.frogsinspace.at/?p=1227 ), but it was also a step too far in terms of stability for some projects, and in the end we went back to 3DSMax 2016.

The only other thing I can think to mention is updating display drivers, and cursing W10?

Perhaps the conversion pipeline code for importing between Keyshot and FXB files not working optimally, which wouldn't be at all surprising.

Re: Backfacing color

electrotoast_old — Thu, 21 Dec 2017 17:44:18 GMT

Hey @markus if you select those faces, you can do a flip normal in the edit poly panel, it should fix those. I've had that happen with Rhino files in the past where Rhino (and most CAD apps) don't really care about the normal direction. In Rhino I would have to do a view normals command and fix per surface. Other times, I just didn't worry about it as along as the render would consider everything 2-sided. This can be an issue if the object was exported from a CAD program prior to going into Keyshot. Then when exported from Keyshot, under the hood it still keeps the normal set 'wrong'.

You can also triage these issues using the xView setting of Flipped Faces.

Re: Backfacing color

markus — Fri, 22 Dec 2017 10:29:19 GMT

Hi @electrotoast_old! I know why the normals are flipped, and I know how I can fix them by manually selecting faces and flipping in edit poly (too much work). That's not the issue though. The rendering is fine since V-ray renders 2-sided surfaces. The problem is just in the viewport. It works fine some of the time, but it keeps switching the shading of backfaces to black (in the viewport) every time I start rendering in Vray framebuffer. I'll try to make a screencast when I find more time, so you can see exactly how it is triggered.

Re: Backfacing color

markus — Fri, 22 Dec 2017 13:56:06 GMT

@electrotoast_old: On a side note, here is the reason I imported to Keyshot first, then transferred it to max via FBX.

I hope your team has time to prioritize improving CAD importers for the next iteration of Max. If you need I can send you some test files you can use. We create a lot of models in Catia and Solidworks, and I'm sure we can find some examples you can use for testing.

Anyways, Happy Holidays, I'm taking the next week off! See you in the new year!! 🙂

3dsmax STEP conversion (ATF to mesh)3dsmax Step Conversion (ATF to mesh)Keyshot Step Conversion (resulting in better surfaces from the same file)

Re: Backfacing color

JezEmin — Sun, 24 Dec 2017 19:10:43 GMT

I've seen this kind of behaviour myself and usually been too engrossed with my project to stop working on that to start identifying why things like this happen.

I *usually* associate this type of behaviour to being NVidia driver related. I'd gotten the 1080ti's soon after they came out and have noticed my viewport performance has improved over time from a while ago (can't remember the last time I experienced what you mention).

So, might be worth taking a look at that side of things.

PS - I'm on 3DS Max 2017 and V-Ray 3.60.04.

Re: Backfacing color

markus — Tue, 02 Jan 2018 13:16:46 GMT

Hi,

I took the time to record a screencast to show how it is triggered, and I hope it clarifies what I mean.

http://autode.sk/2A5YX7F

The problem is not that the model has backfacing surfaces in the first place, since that doen't affect rendering. The problem is just that the viewport changes when I start rendering with V-ray IPR. The Vray materials are 2-sided, but it changes in the viewport while in IPR rendering mode. To reset it I have to make a change to the material in the Material Editor, and that refreshes the material in the viewport. It's not a huge deal but it has to be done for each material.

I'm not sure if this is an issue that must be fixed by Autodesk or if it's something Chaosgroup can take care of on their own. I've posted in both forums now.

[edited. I forgot to finish a sentence].