@aGorm/Everybody:
Welding is, basically, the process of
eliminating un-needed vertices from a model, for maximum efficiency while rendering.
Any 3D model consists of 3 or more points in space, which form the corners of the polygon. These corners are known as vertices.
When two or more vertices meet in space, it is more efficient to simply combine them into one point, thus saving the amount of XYZ data being stored, sorted, and then sent to the rendering pipeline. This is what welding essentially does.
However, due to the nature of rasterizing rendering, welding has other benefits. Good welding can give a model's "rounded" areas a much more rounded look within a 3D engine, because the engine can average things like light sources across multiple polygons that form the welded mesh. This gives things a smoother appearance than would normally be the case- after all, unless a mesh's resolution is so fine that one face < one pixel, it's essentially a collection of flat planes in space.
Welding can cause serious problems, however, if your models aren't carefully made. When the vertices are welded together, they may form surfaces with "bad" vertices. These are vertices where one or more n-gons (the formal term for a polygon of n-vertices) formed by them results in a surface that is not valid- i.e., it is concave, or twisted.
This causes rendering problems. When the rasterizer goes through the model and hits bad vertices, it may even fail entirely, because it cannot evaluate the geometry. Usually, though, it just causes really horrible-looking dark smears on the model, caused by the renderer being unable to determine which side of the polygon is "out".
To prevent these problems in low-poly mesh modeling, follow some basic rules of thumb:
1. If you can model it with discrete, sharp edges and
then weld instead of modeling with mushy curves, do so.
2. Model using booleans and lofting whenever possible. Avoid direct editing of the mesh unless you are sure what you are doing, and always look very critically at the results. It's very easy to create badly-welded models, for example, by modeling a mesh at X size, then scaling it later on. If you're going to scale, do it early, before you're turning the pieces. If you have to get something perfectly fitted at an odd angle... do a test, write down the scalar values used, then do it again with the model in rest position. I have stressed modeling in rest position before, but this is yet another reason to do so!
Those of you using Wings are in a somewhat-bad fix. You don't really have super-good boolean tools, and based on my attempts to work with it, it's not exactly a super tool for doing scalar work with.
However, there are ways around its problems. Several software tools exist for working with meshes and fixing the flaws- including UVMapper Pro, which is what I use. You can, for example, completely unweld a model in UVMapper Pro by using the Split By Angle feature, and giving it a split angle of 179.9999 degrees, which will effectively un-weld the entire model by forcing all non-planar polygons to have discrete vertices. There are other tools out there that can do these things as well (yes, some of them are free, although I don't really recommend them).
To see, a lot more clearly, what welding problems look like, see this sterling example shot:
As you can see, this model has a very serious welding flaw. That back triangle on the "house" is black because it and the other triangle that form the "wall" were welded together, and the back verts, which were welded to the "roof", etc. apparantly twisted the face. I tried un-welding this in Rhino3D (my primary modeler) and it didn't work. I could've split it all out in UVMapper Pro, but quite frankly, if I have to do
that much work to save geometry that would take me 3 minutes to make myself in Rhino, I don't bother
I dont even know what welding is yet.
