This is something I've been wondering for a while as I was using some Doom 3 models for testing my renderer.

Here's a screenshot.

http://i.imgur.com/J7O3iK9.jpg

Notice how down the middle, he has those seams. This is using my deferred shading engine and when I look at the normals in the Gbuffer, the normals are also full of seams there, while the diffuse output looks fairly OK.

The legs also have some nasty texture seam artifacts going on, and I can see these horrible seams when I render the specular gBuffer as well and see how the specular textures map on. The insides of the arms look especially bad.

I remember back in the day on my shitty graphics card, I'd have some seams down the middle of models and it seems to be a complaint around the web people have had. Forcing the normal maps to be uncompressed seems to have been the fix, and nowadays when I play Quake 4 and Doom 3 on higher than ultra settings by tweaking some cvars, I never see these seams.

My renderer is just loading the normal maps as they are in tga format in the .pak. I saw some dds textures in the paks as well and I assume Doom 3 actually uses those, but I don't have a dds texture loader just yet. (I'm also surprised at how much scratch work and useless stuff is inside the pak files that isn't really used by the game, but I'm also really greatful it's there)

Here's a forum post where they actually say to enable some sort of compression on normal maps.

http://forums.cgsociety.org/archive/index.php/t-182031.html

This is a common problem when baking normals, and can be improved by blending the connected pieces to together.

This is usually avoided by placing the seams in a unseen place like below the arm on the side, the only reason I can think of doing it like this is if a model is viewed from behind 95% of the time.

OK, I was actually using Assimp to convert the md5s to my own format. Maybe Assimp is messing something up. I might try to take a look. I can try debug drawing the tangents on the model and making sure they face opposite directions, which I think would indicate the handedness switch?

I'm not sure how to explain the ugly seams at the legs though.

One problem with md5mesh format is that it does not store normal vectors, so the mesh needs to be smoothed after it is loaded. If the artist used some custom smoothing schemes when baking the normals, the renderer has no chance of getting the correct results. I guess that Doom 3 smoothes the meshes uniformly or uses some sort of fixed threshold smooth angle, which is then also used when baking the normal maps.

Note that at texture seams, there are degenerate vertices, which should have the same normal. To properly smooth the mesh, it is not sufficient to compare if two faces share the same vertex index, but you must actually compare the vertex positions, possibly with some threshold distance.

OK, maybe Assimp needs to be tweaked. I don't really intend on using Doom 3 models for ever though, just while I'm developing because they're so friggin cool. Our artist would export things as Dae, With Normals, and then this would probably not be a problem for our real assets.

looks like when you make half of a body in 3d and you dont weld the vertices at the seam.