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Design Considerations for the StylusInput API

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The following are design considerations for the StylusInput API.

  • You can update the WindowInputRectangle property of the RealTimeStylus object and the ClipRectangle property of the DynamicRenderer object while the pen is down. This can be useful when you want to have a dynamic drawing area while the application is collecting ink.

  • To optimize reuse and maintenance of plug-in code, plug-ins should not make calls directly to the application but should use the CustomStylusData (CustomeStylusData object in managed code) to communicate with the application.

  • The RealTimeStylus object's plug-in collections are ordered. The relative position of your plug-ins within these collections can be very important. For example, a plug-in that modifies packet information should probably be added to the synchronous plug-in collection before a dynamic-renderer plug-in.

  • The ability to add custom stylus data to the tablet pen's data stream should be used sparingly. Use this feature only if another plug-in needs to receive this information as part of the data stream. Also, avoid adding custom stylus data in response to other custom stylus data coming into the plug-in, as this can create an infinite loop.

  • Plug-in collections can be modified while the RealTimeStylus object is enabled; however, this can make the behavior of your application harder to predict. When a plug-in is added while the RealTimeStylus object is enabled, the RealTimeStylus object calls the plug-in's Microsoft.StylusInput.IStylusSyncPlugin. RealTimeStylusEnabled method (either the Microsoft.StylusInput.IStylusSyncPlugin.RealTimeStylusEnabled or the Microsoft.StylusInput.IStylusAsyncPlugin.RealTimeStylusEnabled method in managed code). When a plug-in is removed while the RealTimeStylus object is enabled, the RealTimeStylus object calls the plug-in's RealTimeStylusDisabled method (either the Microsoft.StylusInput.IStylusSyncPlugin.RealTimeStylusDisabled or the Microsoft.StylusInput.IStylusAsyncPlugin.RealTimeStylusDisabled method in managed code). This allows the plug-in to maintain its proper state without having to check the Enabled property of the RealTimeStylus object.When a plug-in is added while the RealTimeStylus object is enabled, the plug-in data that the plug-in receives may not contain enough information to adequately establish the context of the initial data. For example, the newly added plug-in could start receiving packet data from a pen that is mid-stroke. Similarly, when a plug-in removed while the RealTimeStylus object is enabled, the plug-in data that the plug-in has received may be insufficient to finish processing the data.

    Note

    For overall stability, reset a plug-in's internal state when either its RealTimeStylusEnabled or RealTimeStylusDisabled method is called.

     

  • The RealTimeStylus object throws an exception if a plug-in modifies the plug-in collection to which it is attached. This happens only when the plug-in does so while it is being called by the RealTimeStylus object as a member of that collection.