From 4e2ea8e4d851a0ea1f910c3001e5c2ddb9ff528c Mon Sep 17 00:00:00 2001
From: Lars Brinkhoff <lars@nocrew.org>
Date: Mon, 25 Jun 2018 12:46:57 +0200
Subject: [PATCH] Information about ARDS graphics.

---
 doc/_info_/ards.info | 72 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100755 doc/_info_/ards.info

diff --git a/doc/_info_/ards.info b/doc/_info_/ards.info
new file mode 100755
index 00000000..0baa8063
--- /dev/null
+++ b/doc/_info_/ards.info
@@ -0,0 +1,72 @@
+
+ARDS GRAPHICS
+
+   ARDS uses an ASCII character to enter one of three graphics, remains
+in that mode for 2 or 4 characters of argument, then stays in that mode
+until explicitly changed to another mode.
+   The modes are as follows:
+
+   MODE		args	octal	ctl	comment
+   character	-	34	^\	leave graphics mode *
+   set-point	4	35	^]	absolute coordinates
+   long-vector	4	36	^^	relative, visible/invisible,
+					solid/dotted
+   short-vector	2	37	^_	visible vectors only
+ 
+ Notes:
+ * Character mode is entered by receipt of any ASCII "control"
+character,   and the control function (eg CR, FF) is also executed.
+  An ARDS does not have a control function associated with the ASCII
+character   34 (GS, ^\)
+ ** short vectors are nice "fast" ways of doing curves, especially over
+slow TTY lines.
+ 
+   Argument characters are in the range 100 <_ a <_ 177 (@ to DEL)
+ 
+ SETPOINT ABSOLUTE FORMAT
+ 
+   --35--  --x1--  --x2--  --y1--  --y2--  --**--
+ 
+ X and Y coordinate information are sign-magnitude numbers
+ x1, y1 are the low order bits;  x2, y2 are high order bits
+ 
+ x1 = < |X| & 37 > _ 1 <ifl x, + 1> + 100
+ 
+2i.e: shift left 1; if < 0 add 1; then add 100
+
+ x2 = < |X| _ -5 > & 37 + 100
+ 
+ y1 like x1
+ 
+ y2 like x2
+
+** since setpoints do not plot, it is not useful to stay in setpoint
+mode - this should be followed by an escape to character mode, or one
+of the vector modes.
+ 
+ LONG-VECTOR RELATIVE FORMAT
+ 
+   --36--  --x1--  --x2--  --y1--  --y2--  --...--
+ 
+ x1, y1 are like setpoint, only they specify relative coordianates
+instead of absolute
+
+ x2 ditto, + if invisible then 40
+ 
+ y2 ditto, + if dotted then 40
+ 
+ ... additional groups of four characters follow, doing more vectors,
+until a  control character comes.
+ 
+ SHORT-VECTOR RELATIVE FORMAT
+ 
+   --37--  --x1--  --y1--  --...--
+ 
+ x1, y1 are like setpoint
+ 
+ note that only the low order character is sent for short vector, so
+"invisible" or "dotted" may not be specified.
+ 
+ note |x|, |y| < 40 (8)
+
+
\ No newline at end of file