42 chapter 2 ■ Sculpting in ZBrush
Backface masking is useful when you’re working on thin meshes such as clothes, wings,
or other objects where the front and back faces are close together. If you are dragging a stroke
on an object where the thickness is less than the size of the brush, often the stroke will carry
over to the opposite side. Backface masking eliminates any faces other than the ones on the side
on which you are working, thus reducing this problem.
The Gravity modifier is found under the Brush → Depth menu. This modifier helps repro-
duce the effect of gravity or wind on a surface. Faces are shifted in the direction of the arrow in
relation to the model’s current position on screen. To use this modifier, select the Gravity arrow
and position it in the direction you want the force to pull. Then, adjust the slider for the correct
strength. This works well for folds of skin with the Inflate or Elastic brush; it helps introduce
the effect of weight on hanging folds of flesh. The Gravity modifier is also helpful when you’re
sculpting drapery—positioning the arrow horizontally can create the impression of wind bil-
lowing in a fabric. In Figure 2.9, the Standard brush was used to create the stroke on the top.
On the bottom, the same brush was used with the addition of a Gravity modifier. Notice how
the weight of the stroke is along the bottom edge as if it is being pulled down. Keep in mind
that this effect is relative to the model’s position on the canvas at the moment of the stroke, not
its pivot point. You could easily sculpt the effects of wind by simply changing the direction of
the Gravity modifier arrow.Gravity OffGravity OnSide ViewWeight is added to the stroke,
pulling it in the direction of
the arrow.Figure 2.9 The Gravity modifier mimics the effect of gravity on the stroke.Cavity masking masks out the recessed areas of the sculpture, allowing you to paint and
sculpt only on the high points. This effect can be tuned using the options under Brush →
Masking → Cavity. This same mask is also available under Tool → Masking → Mask By Cavity.
Figure 2.10 illustrates the effect of this button. The difference between the cavity masking in
these two areas is that the Cavity Masking command in the Brush menu is controlled by the
curve but there is no visual indication of what areas are masked. This brush-based cavity mask-
ing is a real-time masking function that updates and changes as you sculpt the mesh. The cavity
masking available under Tool → Masking does not change in real time. When using Tool →
Masking → Mask By Cavity, you’ll see which areas are masked; however, the mask is set and
will not update as the surface is changed. In many cases this may be desirable as it allows you to
isolate the high or low points on a sculpture and modify only those areas in the confidence the
masked areas will not be affected (Figure 2.11).