The simplest time dependent interactive objects are animated variables (integers, floats or doubles). This class is a bit exceptional, since displaying a variable has no meaning in a graphic scenery, so this class should of course not be used inside the scene hierarchy. It is described here, because it has the same philosophy as the previous classes.
A time dependent variable is controlled by a function. Controlled means, that the function is in some sense hidden for the user. The user only works with a variable, but the variable will be updated by the system automatically when time changes.
Animated variables are implemented in GRAPE by the class Function_Ruler. The function is a spline, it can be modified by a spline-editor. To activate the automatism the user only has to create the function-ruler which controls his variable.
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