[Insight-developers] testing modified times of process objects

[Will Schroeder]

Usually the time stamp (i.e., modified time MTime) is used (rather than a boolean) because it is built into itkObject and is the the basis of the pipeline update mechanism. In some situations I have used another one or two instance of itkTimeStamp to keep track of things in the filter that might take a lot of time to compute, and only depend on a small part of the object input (ivars). It's also important to not just send Modified() to a class when a variable is set - it should be compared against the previous value. Otherwise you'll find that some GUI's - when "Apply" is invoked - set the value of all the ivars they control, and if this comparison is not done the filter thinks it's modified even though nothing actually changed.
Will