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+.help gterm Dec86 "Vector Graphics for the Sun Workstation"
+.sp 2
+.ce
+\fBVector Graphics for IRAF on the Sun Workstation\fR
+.ce
+Doug Tody
+.ce
+December, 1986
+.ce
+(design document)
+.sp 3
+.NH
+Graphics Terminal Model
+
+    The window based, native vector graphics facility for Sun/IRAF will be
+implemented as a purely data driven interface based on the concept of an
+intelligent virtual graphics terminal.  The virtual graphics terminal will
+be implemented in software as a process running under a window system such
+as Sunview or X.
+
+A virtual terminal interface will allow the Sun workstation to be used as an
+ordinary graphics terminal to access IRAF or other software on either the
+local or a foreign host via any data stream interface, e.g., rlogin, telnet,
+or a modem connection.  For example, one will be able to use telnet running
+in a GTERM window to login on a VMS machine, then run IRAF on the VMS machine
+in the normal fashion.  Conversely, since the IRAF software on the Sun node
+will always think that it is talking to a conventional data driven graphics
+terminal, the Sun/IRAF software may in fact be run from a conventional
+graphics terminal, via either a direct or remote login.  Finally, a pure data
+stream TTY interface where all details of the windowing system are isolated
+into a server process makes it possible for a single version of IRAF to support
+multiple window systems on the same host.
+
+The graphics terminal to be implemented by GTERM shall consist of independent
+text and graphics frames.  These will be implemented as separate windows
+(frames) under SunView, allowing them to be moved, resized, exposed, hidden,
+open, closed, etc., independently of each other.  Note however that since both
+frames are connected to the controlling process via a single terminal i/o
+connection, the controlling process (e.g., the CL) can only read from or
+write to one frame at a time.
+
+In normal use, the user will work for a time in the text frame, issuing
+commands to run tasks which do not require interactive graphics facilities.
+When a graphics program is run the graphics frame will be opened or exposed
+and the plot drawn.  If the graphics program is interactive, i.e., uses
+cursor input, the cursor will be moved to the center of the window and the
+crosshairs turned on to indicate that cursor input is required.  A sequence
+of keystroke or mouse button triggered cursor reads will follow, and
+eventually graphics mode will be exited by transmission of the close
+workstation sequence to GTERM by GIO running in the applications program.
+
+When graphics mode is exited GTERM terminal i/o is redirected to the text
+frame and the cursor is restored to its former position in the text frame,
+automatically restoring interactive control to the text frame.  The graphics
+frame may or may not be closed or hidden, depending upon the GTERM defaults
+set up by the user.  If the graphics frame is to be closed or hidden this
+should probably require interactive confirmation by the user, else the plot
+might disappear immediately after being drawn.  Since control naturally
+toggles back and forth between the text and graphics frames and since screen
+space is always limited and a large, high resolution graph is generally
+desired, it is expected that the graphics frame will normally be displayed
+only while in graphics mode.
+
+.NH
+GTERM Graphics Language
+
+    The tektronix graphics language is a simple and efficient standard language
+for graphics terminal i/o which will work about as well as anything in our
+application.  In particular, the vector encoding scheme is simple, compact and 
+efficient, and well suited to use with a variety of terminal drivers and
+modems (since binary data is avoided).  The best approach to implementing the
+GTERM graphics language would seem to be to take the tektronix language as a
+starting point and add additional functionality by extending the language
+with new control sequences.  Some of the extensions defined here a taken from
+the Retrographics vt640 and the Pericom.  Others more specific to window based
+applications will be added in the future in an upwards compatible fashion.
+
+
+.ks
+.nf
+	GS 		open workstation if not already open
+			    open/expose graphics frame (icon -> full window)
+			    direct terminal i/o to graphics frame
+			    save cursor (mouse) position
+			    issue GS dark vector command (see below)
+	CAN		close workstation
+			    restore control to text frame (restore cursor)
+			    close/hide graphics frame (full window -> icon)
+			    keystroke required to trigger close-window?
+
+
+	GS		(workstation already opened)
+			    enter vector drawing mode, dark vector
+	FS		enter point plot mode
+	US,CR		enter alpha mode
+			    text is drawn in graphics frame
+			    defaults to transparent text, erase permitted
+	ESC CR		enter text mode
+			    lines of text are drawn on status line in
+			    nontransparent (overwrite) mode
+
+	ESC SUB		enter crosshair mode
+	ESC FF		clear screen, initialize drawing modes
+	ESC/f [x,y]	set crosshair position
+	GS [x,y] US	sets alpha cursor position
+
+	ESC[0123]	set character size (normal,2x,3x,4x)
+	ESC[`abcd]	set line drawing style (normal,dotted,dotdash,sd,ld)
+	ESC/[012]d	set drawing mode (set, clear, toggle)
+	ESC/[0123]w	set polyline linewidth (normal,2x,3x,4x)
+
+	Standard screen resolution is 1024 by 780.
+	In graphics mode, chars are interpreted as [x,y] coordinate pairs.
+	In alpha mode, chars are interpreted as characters to be drawn.
+.fi
+.ke
+
+
+A number of extensions to this basic language are being considered for future
+implementation.  Support for color, multiple text fonts, general polymarkers,
+area fill, and possibly cell array are contemplated, as well as simple
+extensions for window control and pop-down menus.  Support for the standard
+textronix features which have been omitted (vector point elimination,
+incremental point mode, status enquiry) is possible.  The interface is easily
+extensible hence there is no need to attempt to define or support such features
+in the initial interface.
+
+.NH
+Implementation Notes
+
+    The GTERM virtual terminal consists of two independent frames, the text
+frame and the graphics frame.  Selection of the frame to which output is to
+be delivered is done at the lowest possible level, i.e., when the read system
+call is issued by the terminal to accept terminal output from the pty
+(pseudo-terminal driver) stream for the terminal.  This is done by linking in
+a custom version of the notify_read() primitive, the low level read primitive
+for notifer based programs.  Output is initially to the text frame.  Output
+is redirected to the graphics frame when GS is seen in the output stream,
+and later restored to the text frame when CAN is seen.  Input is controlled
+independently by the two frames at a high level, hence does not have to be
+switched.
+
+All terminal operations are event driven.  Graphics data is deposited into a
+circular input buffer by an event driven read routine, which can issue
+<ctrl/s>/<ctrl/q> to the terminal driver to control the rate at which input
+is accumulated.  A separate drawing routine running off an interval timer
+is used to process data appearing in the input buffer.  The drawing code is
+always in one of three modes: vector drawing mode, alpha mode (randomly
+addressable character drawing), or text mode (textual output to the status
+line).
+
+.SH
+Appendix: Tektronix Graphics Language (Retrographics vt640)
+
+.ks
+.nf
+       *GS		enter graphics mode; dark vector
+       *FS		enter point plot mode
+	RS		enter incremental point mode
+       *US,CR		enter alpha mode, graphics plane, tek font
+	CAN		disable graphics mode, restore output to terminal plane
+
+	ESC"0g		alias for enter transparent mode
+	ESC"4g		alias for enter crosshair mode
+	ESC"5g		enter light pen mode
+
+       *ESC SUB		enter crosshair mode
+       *ESC FF		clear screen, initialize drawing modes
+       *ESC ENQ		return cursor position, other status
+
+	ESC[0123]	set character size (normal,2x,3x,4x)
+	ESC[`abcd]	set line drawing style (normal,dotted,dotdash,sd,ld)
+	ESC/[012]d	set drawing mode (set, clear, toggle)
+
+	ESC/f		set crosshair position
+       *GS [x,y] US	sets alpha cursor position
+
+	Vector coordinate encoding (max 10 bits = 1024 points res.):
+
+			high y	P01XXXXX
+			low  y	P11XXXXX
+			high x	P01XXXXX
+			low  x	P10XXXXX
+
+	Cursor return structure:
+
+			key	PXXXXXXX
+			high x	P01XXXXX
+			low  x	P01XXXXX
+			high y	P01XXXXX
+			low  y	P01XXXXX
+			trailer	<cr>
+
+	Standard 4010/4012 screen resolution is 1024 by 780.
+	In graphics mode, chars are interpreted as [x,y] coordinate pairs.
+	In alpha mode, chars are interpreted as characters to be drawn.
+.fi
+.ke