RFC 178 (rfc178) - Page 2 of 11
Network graphic attention handling
Alternative Format: Original Text Document
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