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Documentation Table of Contents

Input event filters are all subclasses of the arIOFilter class. Filters are attached to an arInputNode (generally by the DeviceServer program, see the Input Devices chapter), which maintains a list of them and passes any events it receives through them.

Creating filter subclasses is quite simple. You need only override the protected virtual method

  virtual bool arIOFilter::processEvent( arInputEvent& inputEvent );

This method will be called by the arInputNode for each event in the input stream. Is is passed the current event, and can do the following things:

• Get the current event's type, index, or value using the appropriate methods of the arInputEvent class.
• Get the most recent value of any other event using the arIOFilter's get...() methods.

• Modify the current event's index or value (<span style="font-style: italic;">not its type) using the arInput.set...() methods.
• Set the current event's value to the default (0 or the identity matrix) using its zero() method.

• Flag the current event for deletion using its trash() method.
• Insert a new event of any type, index, and value into the input stream using the arIOFilter's insertNewEvent() method.

That is all. For examples of working filters, see src/drivers/arTrackCalFilter.cpp (which applies the calibration correction for our Ascension MotionStar tracker--note that this is specific to our setup) and thePForth filter, src/drivers/arPForthFilter.cpp.

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