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Ulm's Oberon Library:
Plot5Streams

NAME

Plot5Streams - traditional Berkeley plot streams

SYNOPSIS

PROCEDURE Create(VAR plotter: Plotters.Plotter; out: Streams.Stream);

DESCRIPTION

Plot5Streams provides an implementation of Plotters that generates traditional Berkeley plot streams. Independent from the current architecture, all binary numbers are generated in little-endian format.

Some options for viewing Berkeley plot streams:

The plot(1) command from the GNU plotutils is able to convert Berkeley plot streams to a large number of file formats and devices. Note, however, that ``-l'' has to be specified as option because by default Berkeley plot streams are only correctly recognized on little-endian architectures.
The BSD plot(1b) utility allows to convert plot streams to a small number of formats.
The Solaris postplot(1) filter allows to convert plot streams into PostScript. This filter is part of the SUNWpsf package and installed as /usr/lib/lp/postscript/postplot.

Create creates a plotter that generates the Berkeley plot instructions onto out. The plotter acts as forwarding object in the sense of Forwarders, i.e. the plotter dies if out terminates, and error events of out are forwarded to plotter.

DIAGNOSTICS

All error events generated by the underlying stream are forwarded to the plotter object. In case of failures, all subsequent operations are silently suppressed.

EXAMPLE

Following procedure opens a plot stream that sends all plot instructions to the plot(1) utility using a pipeline:

PROCEDURE CreateXPlotter(VAR plotter: Plotters.Plotter;
                         errors: RelatedEvents.Object) : BOOLEAN;
   VAR
      out: Streams.Stream;
BEGIN
   IF ~UnixPipes.Open(out, "/usr/local/bin/plot -l -T X",
         UnixPipes.write, Streams.onebuf, errors) THEN
      RETURN FALSE
   END;
   Plot5Streams.Create(plotter, out);
END CreateXPlotter;

Note that out is automatically closed as soon as plotter closes because plotter is the only object that references out.

BUGS

Note that different plot utilities come with different interpretations and different bugs. GNU plot(1), for example, redefines the current position after drawing an arc while postplot(1) does not change it.

Edited by: borchert, last change: 2004/04/22, revision: 1.2, converted to HTML: 2004/04/22