Backface normals lighting question

craigrmsmith

I've just recently got back in to 3d modelling and have spent the past three days solidly trying to work out bump maps etc.

I'm building a treasure chest and for some reason. My mirrored UV's seem to be lit from the back of the faces, as if they are using the same lighting direction as the original UV's.

Now reversing the normals fixes this issue, but surely when I import in to an engine those faces are going to be invisible as they are facing inside the model then?

I've tried flipping the UV's etc but again that doesn't fix the fact the faces are being lit from behind.

Just wondering if anyone has any suggestions?

craigrmsmith

http://imgur.com/ZjfNmM8
http://imgur.com/BfPDvYV

Here's a screen grab of what I mean. Hope that makes sense what I've said

Eric Chadwick

Good to put some more info in your post, like what software. Looks like Maya. Are you using Transfer Maps or some other baker?

Did you offset the mirrored and overlapped UVs at least 1 unit before baking? Only 1 forward-facing copy of the UVs should be inside the 0-1 UV square.

Did you Freeze Transforms before baking?

craigrmsmith

HI,

I'm using Maya 2014. I tried overlapping UV's then offsetting by 1 and that didn't work. This second one I did the normal map using transfer maps. I then redid the UV's for the mirrored sides and then offset by one.

Here's how they look now. http://imgur.com/mNZxUsp

I froze transformations and deleted history before baking.

They display correctly but only if I reverse the normals. But then the normals are facing inside the model. On the above pic of the UV editor it's the two offset shells that seem to be backwards I guess is the best way to describe it.

Eric Chadwick

The model has backfaces removed, right? What does the normal map look like?

craigrmsmith

Sorry I'm not entirely sure what you mean by removed? Turning double sided on/off in the object settings doesn't change anything if that's what you mean? sorry if that's really dense of me.

This is the normal map.
http://imgur.com/l6GJ1cD

Eric Chadwick

Ah, this is a world-space map. You can only mirror if you have a custom shader that mirrors worldspace maps.

craigrmsmith

Oh... Is that the way I baked the normal map so I need to use a different setting? Also how could you tell that just by looking at the map?

Thank you for the help it's greatly appreciated

craigrmsmith

I just re-bake it and it works perfectly now haha, one setting in the baking process caused me a 2 day headache... Ah it's just like being back at uni. Thank you so much for the help!

Eric Chadwick

Tangent Space maps are mostly bluish-purple. Object Space maps (also called world space, same thing basically) are rainbow colored.

Yeah, it's an option in Transfer Maps. http://download.autodesk.com/global/docs/maya2012/en_us/index.html?url=files/Lightingshading__Transfer_Maps.htm,topicNumber=d28e525558

Also, it helps to embed your images in the post... Click on your image in imgur until you get to the largest size, copy the URL (yours ends with .png), then here in the forum click the yellow Insert Image button, and paste your url.

craigrmsmith

Thanks, I'll make sure I do do that from now on and thank you again for the help.