Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 155

Fig. 10.12 An object made of three parts and its UVs
Calculating Texmap Size
Resolution contrast (Sect. 8.10 ) happens when adjacent objects are textured with
maps that have different pixels-per-linear-unit ratios. Regardless of what the difference
is, if there is a difference, one object will look crude compared to the other. Projecting
your coordinates while using a global size reference will avoid this problem
for objects that share the same material, but what if they don't? What if you have
several materials, and you have to use as much of each map as you can by fi lling the
texture space completely (Fig. 10.12 ) . If that is the case, simply projecting the UVs
to scale is not enough. You must also modify the size of your texture maps.
In Fig. 10.12 , the text in each reference map for the three materials is about the
same dimensions, indicating that the scale is correct across all parts of the geometry.
In Fig. 10.13 , the UVs of each piece are scaled so that each fi lls the UV space with-
out distortion.
Because the largest of the UV groups extended more than 1.0 unit in U, it had to
be scaled to fi t within legal UV space. Because all of the pieces have to match, they
must all be scaled together. Left at this scale, each of the three maps would require
a map of the same resolution, though two of those maps would use much less of the
available pixels than the third.
By using the grid squares in your UV editor as a reference, you may determine
exactly how much of the UV space is being used relative to the largest of the
three (Fig. 10.14 ) . Based on this analysis, if map “3” is 1,024 × 1,024, then “2” will
be 717 × 973, and “1” will be 307 × 840. If you had a square power-of-two size
limitation, you could add the maps for 2 and 3 into one 1,024 × 1,024 map. Instead
of three maps then, you'd have two.
In Fig. 10.15 , the UVs have been scaled non-proportionately to fi ll UV space in
both directions. If you look at the polyset on the left, you will see the original object,
and to its right, the new one. The reference map repeats more times on the new
version than the old, indicating that the texture treatment is higher resolution than it
was originally, although two of the maps are smaller and the third is the same size.