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Using Longlib with Graphics Terminals: The Terminal Package

One of three internal, separate packages used by LONGLIB is the terminal screen graphics package. The LONGLIB graphics library supports a variety of graphics  terminal devices which use  Tektronix graphics formats including:             

  1. VT100 equipped with a Selanar GR100 or GR100+ (Selanar Corporation, Santa Clara, Ca.)
  2. VT125 (VT100 + retrographics)
  3. VT240 and compatibles
  4. VT220 equipped with a Selanar SG220
  5. Tektronix 4010/4014 and compatibles
  6. Tektronix 4107/4109 and compatibles
  7. PC and Mac Terminal emulation software
  8. Graphon GO-235
  9. Xterm program (under X-Windows)

        Other graphics terminals can be used by appropriate modification of the terminal driver routines (CTERM, VTPLOT, NEWVPEN, NEWVCOL). The routines  FRAME and  VPLOTS will also need to be modified. Escape sequences need for terminal initialization and mode switching are handled in the subroutine CTERM. When plotting is not done to the terminal  CTERM and other terminal specific routines are dummy calls. Note: plotting to the terminal is done by accumulating a set of connected line segments created by  PLOT or PLOTVT. The line segments are output to  terminal only when the buffer length of 32 is exceeded or a "pen up" occurs. Consequently, a "pen up" should be issued to force all stored plot segments to be output to the terminal prior to viewing screen, e.g., PLOT(0.,0.,5).

It is assumed that all terminals are configured in a standard fashion. Because of the wide variety of terminal types, the specific settings will not be given in this document.

In designing the terminal driver routines, the design philosophy has been to take advantage of the capability that many graphics terminals have to display both text and graphics independently on the screen. That is, the text and graphics "screens" can be independently cleared, etc. This feature is heavily exploited in this library. Of course not all terminals support this feature. Terminals such as the VT240 and Tektronix 4010's do not support this feature. In this case, the  CTERM routine operates somewhat differently in that it sets the terminal to graphics mode and leaves it there.

Note that in the VAX environment, the SET TERM options of the terminal driver must be properly configured. For example, you must execute a SET TERM/FORM while in  DCL to enable the screen clear command to work properly. This permits a form feed to pass through to the terminal. The NO ESCAPE qualifier should also be set to read from the terminal.

A command file, LONGLOC:CLEAR.COM, has been provided which, when executed, will clear the screen of a VT100 equipped with a  Selanar card and set the  VT100 into text mode. Simliar routines for a  VT125 (TCLEAR.COM), a VT220 (VCLEAR.COM), a Graphon (GCLEAR.COM), Tektronics 410x (ACLEAR.COM), and Xterm (XCLEAR.COM) are also provided. These reset the graphics mode back to terminal mode and clear the screens. They can be very helpful during program development.

LONGLIB also supports color on graphics terminals which permit color plotting (Tektronics 410x).





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Next: Terminal Specific Application Up: Introduction Previous: Modifying LONGLIB to



David Long
Wed Jun 12 10:34:11 MDT 1996