duckee opened this issue on Nov 11, 2004 ยท 29 posts
nomuse posted Sat, 13 November 2004 at 4:33 PM
Heh. Crescent beat it to me this time. Think of UV space as a square of graph paper. If you put a dot of paint at the topmost, leftmost square, it will always be at the topmost, leftmost square no matter how big the paper is. If you put a dot of paint in the exact middle, it will always be in the exact middle no matter how big the paper is. If you put a dot of paint half-way between the upper left corner and the middle, it will always be half-way between the upper left corner and the middle. It doesn't matter how big the paper is. This is why you can scale a template all you like. You can even -- and this might get confusing so be warned -- change the PROPORTIONS of the template. However, if you make a template that is twice the height of the original but four times the width, any pattern you paint on it will be placed on the model crunched up or squashed horizontally. That's because you are trying to get, say, forty inches of pattern on to twenty inches of object. I want to step back for a moment and re-iterate that UVmaps are a compromise. Except for the case of a map of a sheet of paper (or a rolled map, or a drapery, or something else that is topologically a simple sheet), the UVmap has to stretch, crunch, and break to fit around the complexities of a solid object. UVmapping is as much art as science, and involves weighing the trade-offs between distortion, useability, and readability. As a simple example: think of a barrel. Obviously you have to introduce at least one "cut" to the surface in order to get a cylinder unrolled on to a sheet of paper. But since the barrel bellys out in the middle you have a terrible choise to make. If you map so the surface remains equal your map has to "bulge out" in the middle -- that means the edges of the staves are all curved lines and hard to paint. If you map so each stave is straight, the texture will stretch around the middle of the barrel, making the wood grain get bigger and coarser there.