RFC 178 (rfc178) - Page 2 of 11

Network graphic attention handling

RFC 178            NETWORK GRAPHIC ATTENTION HANDLING          June 1971


2.1 DEFINITION

   Graphic attention handling refers to the processes and techniques
   whereby human inputs to a computer graphic system are serviced.  An
   attention event, or simply "attention," is a stimulus to the graphic
   system, such as that resulting from a keystroke or light pen usage,
   which presents information to the system.  Servicing includes
   accepting or detecting the hardware input, processing it to determine
   its intended meaning, and either passing this information to a user
   routine or taking some _immediate_ action related to the display
   and/or its underlying data structure, or both.  The emphasis is on
   "immediate."  Attention-handling is not intended to include any
   detailed, application-oriented processing which the attention
   information may indicate is to be performed.  Thus, attention
   handling may be considered separately from any particular
   application.

2.2 INDEPENDENT FROM DISPLAY CONSIDERATIONS

   Not only may attention handling be considered separately from any
   application, but attention generating hardware may be considered
   separately from display hardware.  Oftentimes, it is only
   coincidental that they come in the same package.  Indeed, in some
   configurations an input be processed locally (by the terminal) to
   provide the appropriate response.  For example, a keystroke may or
   may not cause a character to be displayed on a terminal, and the
   logic causing the display may or may not be local (within the
   terminal).  The keystroke might be immediately displayed locally, as
   in the case of an alphanumeric display terminal which buffers
   keystrokes and transmits messages of many characters or it might be
   transmitted to the host computer and "echoed" back for display as in
   teletype-like terminals.

   The question is not limited to such simple input devices as
   keyboards.  So-called "intelligent terminals" with integrated
   programmable logic or even complete small computers can process more
   sophisticated attentions locally, and even alter a local distillate
   of the central (host) data structure without central knowledge.  This
   raises the problem of insuring that the display and the graphic
   application program do not get "out of sync," and requires a more
   expressive protocol from terminal to host processor.










Cotton