From BlenderWiki

SimpleDeform Modifier

Description

The SimpleDeform modifier allows to easily apply some simple deform functions to objects (meshes, lattices, curves, surfaces and texts are supported).

As for most of the deform modifiers, the deform functions are applied to the “computed vertices”, i.e. to the real geometry of the object at the time the modifier is calculated, and not to the original vertices/control points. This means you can increase the level of detail of the deform effect by inserting first a Subsurf modifier (for meshes), or raising the Resol U and V settings (for curves/surfaces/texts).

Using another object, it’s possible to define the axis and origin of the deformation, allowing to apply very different effects.

Options

Deform type

This drop-down list defines the deform function applied, among four available:

• Twist – Rotates around the Z axis.
• Bend – Bends the mesh over the Z axis.
• Taper – Linearly scales along Z axis.
• Stretch – Stretches the object along the Z axis (negative Factor leads to squash).

The different deform functions, from left to right: Twist, Bend, Taper, Stretch with positive Factor, Stretch with negative Factor.

VGroup

The name of the vertex group that indicates whether and how much each vertex is influenced by the deformation.

Ob

An object that defines the origin of deformation (usually an empty). This object can be:

• Rotated to control axis (as it is its Z axis that is now used as “guide”).
• Translated to control the origin of deformation.
• Scaled to change the deform factor.

Factor

The amount of deformation.

Upper Limit and Lower Limit

These settings allow you to limit the part of the object that is affected by the deformation (they are proportional values, from 0.0 to 1.0). Obviously, Upper Limit can’t be lower than Lower Limit…

The various deform functions with Upper Limit set to 0.75 and Lower Limit to 0.25.

Lock X/Loc Y (Taper and Strecth types only)

This controls whether the X and/or Y coordinates are allowed to change or not. Thus it is possible to squash the X coordinates of an object and keep the Y coordinates intact…

A Stretch SimpleDeform modifier without lock, with Loc X, and with Loc Y.

Notes

When the object controlling the origin (the one in the Ob field) is a child of the deformed object, this creates a cyclic dependency in Blender’s data system (the DAG – “dependency graph”?). The work around is to create an empty and attach both objects to it…