Activating the ShadowBox toggle draws a three sided ShadowBox offering the ability to paint masks and generate a 3D mesh.
ShadowBox generates the model in three dimensions based on the drawn mask shapes.
The left example (above) demonstrates that when a mask paints to one third the dimension of ShadowBox, no mesh is generated. The right example (above) demonstrates that Masks applied to two-thirds dimensions result in a generated mesh.
ZBrush for iPad Shadowbox features work the same as in ZBrush desktop. Learn more in external ZBrush ShadowBox documentation.