UV Unwrapping - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 111

and then use a single (nontiling) image to uniquely
texture each part of the object's surface. Both options
are shown in Figure 8-3.

(In order for this process to work for a closed
mesh, you'll need to mark some UV seams on
your mesh.)

Smart UV Project This will automatically project
your mesh by first projecting the largest chunk
possible from one angle, excluding invisible
faces or ones that point away from that viewport.
It will then project progressively smaller, more
difficult parts, splitting them into different UV
islands as it goes. This effect can work reason-
ably well for simple meshes, but when used with
more complex shapes, it often produces a lot of
little islands that can be difficult to work with.

Lightmap Pack This special UV unwrapping
option for baking lighting to textures projects
each individual polygon in a mesh to a separate
rectangular UV island. The Lightmap Pack
option uses up the UV coordinate space very
efficiently, which makes it useful for baking
lighting textures for game engines but not very
useful for practical texturing.

Follow Active Quads This follows the active quad
(the one highlighted when you have multiple
faces selected in Face Select mode—usually the
most recently selected one) and unwraps the
faces radiating out from it in an even grid. This
option works particularly well for meshes with
grid-like topology (that is, no poles), such as
pipes, cylinders, flat(ish) grids, and the like.
It works best when you unwrap one quad first
as a perfect rectangle with 90-degree corners:
1) Unwrap with U 4 Unwrap ; 2) select each edge
of the unwrapped quad in the UV Image editor
and scale it so it's perfectly horizontal/vertical;
3) unwrap the rest of the mesh by selecting it
with ctrl -L, which selects anything connected
to your current selection; 4) use the Follow
Active Quads unwrap operator to get a nice
even unwrap. This option, though, doesn't work
well for meshes with more complex topology.

Figure 8-3: Two options for UV unwrapping. Top: Packing
all of an object's faces into the UV grid to texture each part
uniquely. Bottom: Tiling an image over an object's surface.

When creating objects with fairly repetitive or
homogenous textures, such as brick walls or soil,
tileable textures can save you a lot of time. On the
other hand, when creating characters and other
unique objects, you'll need to pack an object's UVs
onto a single grid in order to texture each part
differently.

Unwrapping Tools
To start unwrapping a model, you'll need to be in
Edit mode (press tab to switch into it if you aren't
already there). You'll probably also want to switch
to Edge Select mode in the 3D Viewport header, as
tagging edges with UV seams is easiest when you
can select edges directly. To begin unwrapping your
object, press U in the 3D Viewport, which will bring
up several operators for unwrapping your object, as
shown in Figure 8-2. These operators are as follows:

Cube Projection This option projects the faces of
your mesh as if on the surface of a cube. It's use-
ful for roughly cube-shaped objects.

Cylinder Projection This option works like Cube
Projection but acts as if the mesh is cylindrical.

Unwrap This is probably the most useful UV
unwrapping method. Blender will try to unwrap
your mesh by flattening it as if it were made from
stretchy fabric, while also trying to minimize the
distortion that this flattening inevitably causes.

Sphere Projection This option also works like
Cube Projection but acts as if the mesh is
spherical.