Blocking In - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 33

3D curves have a “tilt” that determines the direction
of extrusion of the curve, as shown in Figure 4-4.
You can see the direction of the tilt from the
normals (arrowheads) displayed along the
length of 3D curves. You can edit this tilt with
ctrl-T, -T, allowing you to create a curve that
twists along its length.

corners. Free handles create sharp corners too,
but you can also grab them and move them
around like aligned handles, allowing you to
create curved segments between control points.

Modifiers
Modifiers allow you to procedurally and non-
destructively perform operations on your models.
They are fundamental to creating just about any-
thing in Blender. Some modifiers generate new
geometry, replacing or adding to your mesh, while
others deform existing geometry according to cer-
tain rules or offer ways to plug simulations and other
more complex entities into your scene.
We'll focus mainly on modifiers that generate
and deform the meshes they are applied to because
they're the most useful for creating models. Some of
the most important ones for modeling are listed in
Table 4-3. In particular, the Mirror and Subdivision
Surface modifiers are used in practically all organic
modeling. The effects of the most commonly used
generate modifiers are shown on a half-sphere in
Figure 4-6.

Curves can be used to deform meshes. Mesh objects
can be stretched along the path taken by a curve
by applying a curve modifier to them.

The curve handles can work in one of several ways,
as shown in Figure 4-5. The default is usually
automatic or aligned, depending on the sort of
curve object you add. Automatic handles simply
create a smooth path from one control point to
the next, with the handles pointing in opposite
directions. If you grab one handle and move
it, its control point will switch to using aligned
handles that point in opposite directions but
can be rotated and scaled, allowing you to
create more flexible curves. You can change to
other handle types using the shortcut V (or via
the Curve menu in the header). Vector handles
create straight lines between points with sharp

Figure 4-4: Different types of curves. Left: A 2D curve extruded
and beveled to make a flat cutout shape. Right: 3D curves
extruded to make ribbons. (The tilt of the curve defines how
the curve twists.)

Figure 4-5: Curves with different handle types (clockwise from
top left: automatic, aligned, vector, and free)