UV Unwrapping - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 119

unwrapping the Spider Bot
For the Spider Bot, I did my best to squeeze the
model's entire UV unwrap onto a single texture
(see Figure 8-13), excluding a few parts that would
receive only procedural materials. Because much
of the model used similar materials, it was easy
to edit the whole texture at once. By starting with
the big elements, like the body and the legs, and
then squeezing the smaller parts into the gaps in
between, I could produce a very efficiently packed
set of UVs, ensuring that important elements got
the texture real estate they needed. You can always
check that the different parts unwrap with the right
scale and without stretching using a UV grid texture
(see Figure 8-13).

Applying Modifiers and Duplicates
In previous chapters, I used modifiers to model and
retopologize the Spider Bot's body and legs symmet-
rically. By doing so, I reduced the amount of work
required and duplicated some of the parts for the
legs. While I could have kept the leg pieces as dupli-
cates, it was better to apply some of the modifiers
at this stage, especially Mirror modifiers, because
otherwise the textures would be mapped to both
sides of the objects symmetrically. This would result
in some obvious symmetry down the middle of the
objects; worse, if I were to use any text or graphics in
my textures, they would appear on the mirrored side
of the mesh backward! For this reason, I applied
the Mirror modifiers assigned to many of the Spider
Bot's constituent objects.
Unfortunately, Blender won't allow you to apply
modifiers to objects that share their mesh data
with other objects. This makes applying modifiers
to the model difficult when, as for the Spider Bot,
I have used linked duplicates to copy parts of the
model, like the legs, which now have many objects
that share the same mesh data. To get around this,
use the Mesh from the Curve/Meta/Surf/Text
operator ( alt -C), which will apply any modifiers
to an object and convert them to proper geometry.
Because you want to apply only the Mirror modifier,
not the Subdivision Surface modifier, remove all but
the Mirror modifier first and then use the operator.
You will then need to remove the Mirror modifiers
from the other duplicates because they will now be
using the already mirrored mesh data.

Figure 8-13: In the case of the Spider Bot UVs, most of the
unwrapping was done with Unwrap. Once I unwrapped it, I
packed all of the UV coordinates for the model to occupy the
same space. (You only need to unwrap each duplicate part
once. So, for example, the parts of the legs don't all need to
be unwrapped separately, as long as the duplicates all use
the same mesh data.)

Sharing UV Space Efficiently
For certain areas, I shared the UV space for simi-
lar parts (see Figure 8-14). For example, for the
mechanical elements beneath the legs, I placed
all of the UV islands on a patch at the top-right cor-
ner of the UV grid. Doing so will cause errors when
baking textures, but by painting a generic texture
over these areas, I can texture multiple parts of
the model without using as much UV space. (Since
these parts are relatively hidden, the lack of unique
textures on these areas won't make too much of a
difference.)