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How objects are used in an HLU programThis module provides some insight into the relationships between objects in HLU programs.
- The App object is used to manage the resource database that will
be used by all of the children of the App object.
An HLU programmer can choose to use, or not use, a local application resource file. There are two cases in which such a file is not needed:
- If the default values of all resources are acceptable
- All resources to be changed are changed in the program through the appropriate NhlSetValues function calls or NhlCreate calls
- A DataItem object is used to bring in data for Plot objects such
as ContourPlot, StreamlinePlot, VectorPlot, or XyPlot.
- A Workstation object is used to direct the graphics
to an X Workstation, to an NCGM, or to a PostScript file.
- View objects are used to generate the graphics. One or
more View objects can be drawn before a frame is completed.
In this context, a frame is either the extent of graphics
sent to an X Window before a pause or window clear is initiated,
or it is the completion of an NCGM image or PostScript page.
- The Error object is created automatically. It is used to buffer and output error messages, among other things.