Normal Map Shading
polycounter lvl 11
I apologize if this has been answered elsewhere in the forums. I read through the pinned normal map thread but I didn't see anything that explicitly addressed my issue.
I have a model that I have been trying to normal map for awhile now but I keep on seeing what appears to be [FONT=verdana, arial][FONT=verdana, arial]per-vertex Gouraud shading[/FONT][/FONT][FONT=verdana, arial][FONT=verdana, arial] in my model.
I thought that once the model was using per-pixel shading you would no longer be able to see any hint of the underlying geometry in the shading.
So is this the case, and I am doing something wrong or am I just confused?
Thanks
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I have a model that I have been trying to normal map for awhile now but I keep on seeing what appears to be [FONT=verdana, arial][FONT=verdana, arial]per-vertex Gouraud shading[/FONT][/FONT][FONT=verdana, arial][FONT=verdana, arial] in my model.
I thought that once the model was using per-pixel shading you would no longer be able to see any hint of the underlying geometry in the shading.
So is this the case, and I am doing something wrong or am I just confused?
Thanks
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Replies
Possibility #1: It could be that your rendering program and your map-baking program used a slightly different method to calculate tangent space, and ended up with slightly different results.
To test this possibility, apply a flat blue (127,127,255) normal map to your object. Do you still see the problem?
If the problem persists with a flat blue normal map, it must be something wrong in your rendering code. See below.
Possibility #2:
If you rule out possibility #1, then it could be a problem with your pixel shader. Without knowing what your shader looks like, I can only offer a generic advice.
Make sure that you're normalize all your unit vectors inside your pixel shader. It's not good enough to just normalize them in your vertex shader, because interpolation between vertices will denormalize them, which might cause something like this.
I tested the model with a comletely flat blue texture and I can still very easily see some of the faceting of the triangulated mesh when I move the light around.... Is this normal, or is xNormal rending things weird?
I'm open for correction.
Also, I loaded ONLY the model up in Unreal 3. With the default material on it I can see the exact same shading problem. So that suggest to me that it has NOTHING to do with my map, and you can indeed see some of the faceting of the model with tangent space normal maps just like TSM said.
If someone could confirm this I would appreciate it. I am just confused as to whether or not I should build my model caring about the per-vertex shading or not. I assumed since everything was per-pixel it no longer mattered and I could cut down on the number of polygons by ignoring shading problems.
If you want to use the former, you will need to adjust the topology of the low-res model. Moving some verts around can help, subdividing/chamfering can also help.
Also, I finally did get the exact result I wanted with TANGENT SPACE normal maps inside xNormal. However I am completely unable to re-produce the effect inside unreal3 with the exact same normal map and the exact same mesh.
If xNormal can take a tangent space normal map and produce the effect that I am seeing then why cant Unreal, is there some fundemental differnce, and is the faceting that I am seeing "normal" for this type of normal map?
Thanks for all your help so far.
This is just guess cause it is usually what gives me problems.
:poly114b: <-- this looks like the normal map smiley. beaten but still happy.
Either select the Green channel in Photoshop and Invert it (Image -> Adjustments -> Invert), or change the Swizzle coords in Xnormal as Odium said.
Flipping the green channel in pshop fixed the shading in unreal. Now I am much much closer to what I am seeing in xNormal. However I still cant figure out why I am getting ZERO faceting in xnormal but I am stilling getting some in Unreal.
Once again is this "normal"? I was inclined to think that but after seeing what xNormal can do with the exact same mesh and texture I am still a little confused.
For 100% perfect match you'll need a programmer though(like did 8monkeylabs with their Stooge importer).... or use object space normals instead of tangent space...
Does anyone know if unreal even uses bitangent data for sure, and how you would go about ensuring its preserved. Would you need to then generate your maps inside your 3D package and then export them using ActorX?
Also how important are bitangents, because in Xnormal I can load up models I have exported fresh out of maya that have never had a normal map rendered on them and load them up in Xnormal with an already rendered map and they look fine.
I am really interested in understanding the topic but the results that I am seeing are telling me that you dont need them? Can somone please clarify?
normal, tangent, bitangent
if tangentsapce of "baker" and "runtime shader" dont match, you will have errors...
creating the tangentsapce is typically done by engine (and/or its tools). Xnormal supports adding custom tangentsapce generators to make sure engine and baker match.
however when you dont know for sure how unreal creates them then you are kind doomed to trial & error of different "generators".
That should help the faceting, but you are also likely to get some along UV seams as the engine sees that as a vertex split/hard edge, and I'm not certain that is accounted for in the normal map rendering of U3.