HowTo:Unwrap
 Creating Ships in Wings3D
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 HowTos
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Creating your own textures 
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This article is intended to cover the topic of unwrapping meshes on both basic and advanced levels.
Contents
Unwrapping Basics
FIXME - write tutorial!
What is a UV map?
How do I unwrap my mesh?
Cautionary note
Please do not use multiple textures, like one for each material... least of all tiling textures. If you're used to modelling but have never modelled for games, you might be in the habit of using multiple textures. That's a unnaceptable for ships or stations--it slows the video card to a grinding halt. Please follow to make a UV map unwrapping to a single texture. And if your favorite tool doesn't do it, we reccomend that you use Blender (or Wings3D for simple jobs.)
Tips and Guidelines
Mipmap Friendly UV-mapping:
For a UV-layout to be mipmap-friendly, you need to subdivide the texture space into zones that are power-of-two fractions of the full texture in x and in y. Zones can be rectangular, of course, but they must meet the following simple rule, independently in both x and y: A zone's starting line must be a multiple of its size.
Example: Let's assume the texture is 1024 by 1024 --rather than speak in abstract terms of fractions of width--, and say you need a rectangular area for a long strip kind of shape, about 4:1 length-to-width ratio, and that you decide it could do with 256 x 64 pixels. With an x-size of 256, good placements are at x=0, x=256, x=512, and x=768. An example of a bad placement would be starting at x=128, not to speak of x=73 or somesuch. That's the reason the grid in the UV window goes by powers of 2 (at least in Blender it does ;-)).
Similarly, you can place that strip, vertically, starting at any multiple of its vertical size (64), such as y=0, y=64, y=128, y=192... but NOT y=32, or y=100.
The reason for all this is that, when the texture is sent to the videocard, mipmaps are generated on the fly, which are progressive downscalings by powers of 2, down to a single texel. At each scaling, each square set of 4 texels becomes 1 texel (average of the four), and the texture becomes more and more filtered. What you don't want is for that filtering to bleed color between islands. Subdividing the texture using the above rule minimizes such inter-island bleeding.
On the other hand, efficient use of the texture is as important as minimizing mipmap artifacts. And such mipmap bleeding is only noticeable if the colors of the inter-bleeding islands are different. Things on neighboring islands that will have similar texturing, therefore, can ignore the above rule, specially if they are continuous on the mesh itself --as in, the two islands being just the result of a seam separation.
Texturing-friendly UV-mapping:
Another guideline specific to WCU (but suggested as well to other mods) is we want to establish a "wind direction": We'd like to standardize the forward (nose of the ship) direction to the left, back (engines) to the right ("wind direction" left to right). Reason is, while working on the texture we can then use motion blurs globally to produce such effects as windmarks and scratches, which extend back from given points. If some of the front-to-back strips are horizontal, and some are vertical, and some go from right to left, wind-direction-wise, it becomes a tedious job to select and motion blur each section separately. Not to speak of other angles...
Neatness:
And since all longitudinal things would be oriended "left is front, back is right", then might as well also align them vertically, front to back (left to right) so that they make sense; and even order them vertically so that they make sense. So, let's say you could think of as grabbing your ship, nose to the left, engines to the right, sit it at the top of the texture, and unroll it down. So, front ailerons, if any, would be left from, and horizontally aligned with, the main wings on the right. It greatly helps with the texturing to have such orderings and alignments. Of course, often this isn't possible: --things like hardpoints and vertical rudders have to have their own islands outside of this unrolling continuum or else they might occupy too much space; but of course, small items can share space with other small items of similar size, rather than obey vertical alignment. But try, as much as possible, to keep some alignment rule, even for the smaller items, that makes it easy to figure out what's what, from where it is placed, rather than make the unwrapping a puzzle or IQ test.
Consistency:
Another general guideline, is keeping the scalings of the various parts on the same level. Exceptions to this could be things you want to look more detailed. Weapon hardpoints, for example, might conceivably use some nice texture greebling: round calibration screws and writings or warnings and locks and whatnot, and therefore could be enlarged, say about 2:1, relative to other parts of the mesh. Any part of the meshe where you plan to have some writing or pseudowriting, might be a good candidate for enlargement.
To overlap or not to overlap:
Okay, those two engines on either side look exactly identical and would use identical texturing, so how about we just grab the island of one of them and place it on top of the island for the other, and only have to texture once? Almost a good idea, I'd say, BUT, if you intend to use Radiosity Baking (and you should), you should not; unless you're going to overlap EVERYTHING that is symetrical, without exception. You can either go for FULL symmetry overlap, or NO overlap; --nothing inbetween. If you only overlap some parts and not others, it makes a mess with radiosity baking.
See also
| Creating Ships in Wings3D
|
HowTos
|
Creating your own textures
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