9.5.2

1068 • CHAPTER 22
XPRESSO EDITOR • 1069
Now suppose you create a new scene, this time of a mother hen walking and her two chicks following.
You create two expressions: Follow Mum (to make the rst chick follow the hen) and Follow Chick
One (to make the second chick follow the rst chick). So that the second chick follows the rst chick’s
current position, Follow Mum must be evaluated before Follow Chick One. Otherwise, the second
chick would follow the rst chick’s position from the previous frame, causing the time-lag problem
once again.
In these cases, use the input box to control the order in which expressions of the same XPriority are
evaluated. Enter a number from -500 to 500 for each expression. The expressions will be evaluated in
numerical order, lowest number rst.
Recall that, provided the value in the input box is 0, the expression will be evaluated at the same time
as the group that you choose from the XPriority drop-down list. If you enter a value less than 0, the
expression will be evaluated before the group. A value greater than 0 will see the expression evaluated
after the group.
Camera Dependent
This option determines whether the expression is calculated and its result displayed while the camera
is being rotated or moved. By disabling this option you can dramatically speed up the redraw rate in
the viewport for some expressions, such as the Target tag.
Data types
Each node and XGroup has a data type that denes the type of value it uses, such as Integer, Vector
or Color. If you connect two nodes that use different data types, the wire between the nodes converts
the data type automatically if the types are compatible. For example, if a Constant node passes a Real
value of 3.45 to a Result node whose data type is set to Integer, the value will be converted to an
integer automatically — in this case, to 3.
Although some nodes have a xed data type that cannot be changed, you can change the data type
of most nodes in the Attribute manager.
Bool
The Bool data type has two possible states: True or False. These states are represented by the numeric
values 1 (True) and 0 (False). Although you can use Bool values in math calculations, keep in mind
that the Bool data type is able to hold a value of 0 or 1 only. When you want to combine several Bool
values, use Logic nodes.