The RELATIVE_SHELLS component consists of a series of movable layers or shells. There can be from
one to five active shells, Shell_Value_1 through Shell_Value_5, along with a fixed Background shell. Each active shell can be moved independently, with its corresponding percent Shell_Position (one
through five) parameter.
Smooth blending is done between adjacent Shell_Values. The Blend_Function defines how the values are blended from one shell to the next and defaults to linear. It is important to note that the blending
between the shells blends from the lower numbered shell to the higher numbered shell. So when a shell gets larger, the shell that is numbered one less than it will also appear to grow. The blending can be
disabled by linking in a generator that is clamped to 100%. This is useful if you want to see where the shells are exactly.
The Mapping_Type parameter determines how the shells are arranged. With Planar mapping mode set, the shells are planar and are layered in a stack. In Cylindrical mapping mode, the shells consist of
concentric cylinders around the Z axis. In Spherical mapping mode, the shells are concentric spheres, like the layers of an onion. The Shell_Position parameters support generators, and this changes based on
the Mapping_Type chosen. For the Planar mapping mode, the generator controls the position from left to right. For Cylindrical mapping mode, the generator controls the position along the Z axis. For
Spherical mapping mode, the generator controls the position around the Z axis in a clockwise direction, starting at the leftmost edge of the circle. In this last case, make sure the generator repeats to avoid
discontinuities.
This component is similar to the Absolute_Shells component, but with one important difference. In the
Absolute_Shells component, you specify the absolute position of each shell and therefore the order of the shells can change. The shells in this component will always be in the same order, only their positions
between each other will change. There are two modes for this texture, controlled by the setting the Absolute_Flag. In both modes, it is useful to think about the shells taking up space inside a region that
goes from 0% to 100%.
When the Absolute_Flag is on, the shells will always fill up the entire space from 0% to 100% and therefore the Background is not used. The Shell_Position parameters are used as weights to control the
relative sizes of the shells. If one Shell_Position is twice the value of another Shell_Position, the size of
the shell will be twice as large as the other shell. The absolute sizes of the shells are scaled so that all the
shells will fill the entire space exactly. Therefore, if only one Shell_Position is changed, all the shells are affected.
When the Absolute_Flag is off, the Shell_Positions are processed in order (starting with shell 1). The
Shell_Position is measured from the previous shell position to the end of the space. If the Shell_Position
is 0%, the shell will be positioned behind the last shell and therefore be invisible. If the Shell_Position is
50%, it will be placed halfway between the previous shell and the end of the space. If the Shell_Position is 100%, it will be positioned at the end of the space and it will leave no room for the remaining shells.
When a Shell_Position changes, it will only affect the shells that come after it. Changing the first shell has the most effect on the texture, and changing the last shell has the least effect. The Background is
used in this mode because there can be gaps at the beginning and end of the shells. If the position of the
first shell is not 0% there will be a gap at the beginning. Likewise, if the position of the last shell is not 100%, there will be a gap at the end.
