A.6. - Optimizing terminal capabilities for PseudoGraphics
Most installations of UNIX operating systems include a facility for describing the capabilities and special character sequences of terminals in a uniform way. On some versions of the operating system, the file /etc/termcap contains the capabilities. On other systems, files in the directory /usr/lib/terminfo are used. The following termcap/terminfo capabilities are used for PseudoGraphics, where the two-letter code is the conventional name of the capability.
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Values for the number of lines and columns on the tty screen are taken from the environment variables
LINES and
COLUMNS, rather
than the
termcap
or
terminfo
databases, if available.
If
these values aren't present, the defaults of 24 lines and 80 columns
are used.
If the
TIOCGWINSZ ioctl()
mode is present on
windowing systems, that command is used to obtain the window size.
Stand-out mode is used in the C-PLOT package when highlighting data points in the video-display version of the command
gd 7
(see Chapter 3), as well in highlighting text displayed
with the help command.
The capabilities
as and
ae are often missing from standard
data bases.
Their function is to start and end translation to the
terminal's alternate character set.
The PseudoGraphics features use
characters from the alternate character set, if available, to outline
the axis, show the tick marks and plot the points.
The codes for the
alternate characters themselves are not generally part of the terminal
capabilities databases.
Thus, the codes for these characters are built
into the plot program, but only for a selected number of terminals.
There are five alternate character sets built into the program. One of these character sets is automatically chosen when the plot program starts up based on the value of the
TERM variable.
The recognized
names are shown in the following table.
The first entry is used when
TERM doesn't match any of the other names.
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If one of the built-in character sets might be appropriate for your terminal but the
TERM name you use isn't built into the program,
you can use the
gr command to select the appropriate name from
the last column of the table.
If the plot program can't find the name
you give with the
gr command in the terminal-capability database,
it will switch to the alternate characters associated with that name
but will continue to use the control sequences it had been using.