The first time I worked on a game doing environments, a programmer came up to me one day and gave me, very gravely, some instructions on how a game engine renders to the screen. The point of the discussion was that, since I was unwrapping models for texturing, I should use fewer UV islands. Every UV island, at least in a game engine, tends to represent a draw call, so the more of those you have then the more costly assets using the texture becomes. For a tree, for instance, if you have two textures (one for the wood and one for the leaves), that's two draw calls. On top of that, if your UV mapping has two islands for the front and back side of the tree trunk, for example, you're adding more draw calls. Games often have lots of trees, so efficiency is the key.
In the following steps we'll look at how to join two texture islands together, continuing from where we left off:
We have a strip of polygons and a flat circle. They are contiguous on the model...