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Realtime rendering- Normals seam problem

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#1

I was wondering if anyone would have any useful information that might help me overcome my realtime normal rendering issue.

The problem i'm having has to do with the seams on various parts of a skull glowing (A-1). The model was unwrapped in Max2009 and I believe that may be where the problem is coming from.

My theory is- the top of the skull has a different orientation than the rest of the skull therefore creating a problem where the normals fight for the proper direction creating a glowing seam.

In Max I have the material set up with Direct X so I can preview the normal in realtime. The glowing seams are visible in the viewport but when the render is made the glow goes away. Looking at the model from a top down view in the viewport the seam only glows on one side of the model (A-2). the only way i've been able to eliminate this problem in the max viewport is by breaking the edges around those seams and then averaging the resulting normals per vertex (A-4). this fixed the glow in the max viewport but not for the software the model was intended for, instead it gave the model a noticeable specular inconsistency (A-6).

As a test I took a neutral normal tone (125,125,255) and applied it to the model and the same glowing seams occurred (A-5). Can this problem be fixed? Any help on this subject would be greatly appreciated.
[NormProb01.jpg]NormProb03.jpg

Attachments

NormProb02.jpg

#2

your glowing is only at the seams of the UV map correct? Is the model “mesh-smoothed” or anything else to it? If you could upload an image of the wire frame that would help to understand the issue. How are you creating the normal maps? Zbrush or Max? Are they tangent space maps or Interpolated? What program is the final image for? Are those seams there when the edges aren’t split with the 128.128.255 in your final program? Are any sections of the map scaled differently (granted, that shouldn’t really matter with the base color applied to the nrml map)

It is most likely a tangent issue, as you said it fixes when you split the model and take the resulting normals.

I have never run into this myself, but I’m sure at some point I will…I seem to find every other problem. I’ll keep checking back on this thread to see where it goes.

#3

The model has not been mesh smoothed but I did export it at the second level of subdivision (I have also tried with original mesh).

It has 1 smoothing group. The normal map was generated using ZMapper and it is a tangent space map. The model goes into an OGRE rendering engine but shows the same problems in the Max viewport. The Scaling should also be consistant between all the pieces. so far the only way ive been able to alleviate the problem was by eleminating some of the seams. but the glowing is still present... [[ATT=]NormProb04.jpg[/ATT]](http://javascript%3Cb%3E%3C/b%3E:zb_insimg%28%27%27,%27NormProb04.jpg%27,1,0%29)[](http://javascript%3Cb%3E%3C/b%3E:zb_insimg%28%27%27,%27NormProb04.jpg%27,1,0%29)

Attachments

NormProb04.jpg

#4

As you’ve observed, it’s a viewport error. Basically, the viewport gives a quick and dirty render of your model, lacking many of the settings that a full render has. Sometimes that creates no problems at all. But with normal maps, it is not at all uncommon to see artifacts in the viewport. Don’t worry about them. The problems don’t exist in the actual render, which is where it really matters.

#5

This model is intended to be used as an educational tool in a realtime rendering, medical related software. so the actual interface it will be displayed in is practically a viewport. like a videogame, almost. im still troubleshooting to see if i can at least reduce the amount of glowing seams but so far, re-doing the uv mapping is the only thing that that made it look better… splitting the edges fixed the glow but creates a different problem.

#6

Have you tried it in the actual engine, though? Very often, problems in an animation package’s viewport go away in the actual engine.

#7

The images from A5 and A6 are from the engine. I think its because my UVs are fudged… im going to unwrap it again and see if i can match the angles of the polygons better and try to get the seam to go vertically instead… it’ll get figured out eventually…

#8

One thing to keep in mind is that tangent space maps like you’re using involve a mathematical routine that forces normal flipping across UV borders. That creates visible artifacts in the render. So with tangent maps it’s always best to lay out the UV’s to hide those edges as much as possible.

There’s also a tutorial here that can help: http://www.zbrushcentral.com/zbc/showthread.php?t=56882

#9

Well, we finally discovered that it was a problem with the shader code, but now another problem has presented itself. This one ive actually seen before though, ive just never found out or asked if anyone knew how to fix it.

The problem has to do with the seams opening up as I zoom out on the model. I dont know if this is unavoidable by just hiding the seams better but it seems like it would be fixable…

any help is appreciated.
[NormProb07.jpg](javascript:zb_insimg(‘113868’,‘NormProb07.jpg’,1,0))