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Choosing a Graphics Package

The PlotPlot class itself does not include any code for actually drawing on a graphics device. Instead, it requires a set of functions to be provided which it uses to draw the required graphics. These include functions to draw a straight line, draw a text string, etc. You may choose to provide functions from your favorite graphics package, or you can even write your own! To accomodate variations in the calling interfaces of different graphics packages, AST defines a standard interface for these routines. If this interface differs from the interface provided by your graphics package (which in general it will), then you must write a set of wrapper functions, which provide the interface expected by AST but which then call functions from your graphics package to provide the required functionality. AST comes with wrapper functions suitable for the PGPLOT graphics package (see SUN/15sun15).

There are two ways of indicating which wrapper functions are to be used by the Plot class:

1. A file containing C functions with pre-defined names can be written and linked with the application using options of the ast_linkast_link command. (see §3.3 and Appendix E). AST is distributed with such a file (called grf_pgplot.c) which calls PGPLOT functions to implement the required functionality. This file can be used as a template for writing your own.

2. The astGrfSetastGrfSet method of the Plot class can be used to “register” wrapper functions at run-time. This allows an application to switch between graphics systems if required. Graphics functions registered in this way do not need to have the pre-defined names used in the link-time method described above.

For details of the interfaces of the wrapper routines, see either the grf_pgplot.c file included in the AST source distribution, or the reference documentation for the astGrfSet method.