/*   FSC-0025








                                                        Pittsburgh, PA
                                                        23 August 1988










                             A V A T A R

      Advanced Video Attribute Terminal Assembler and Recreator

                          George A. Stanislav

                                 129/39



                          Historical Overview


Wynn Wagner III, the author of Opus-CBCS, developed a method of storing
video control codes in a file sent to the Opus caller which was meant as
a replacement of ANSI escape codes. Its main advantages were:

        o  The codes are smaller than ANSI, thus needing less disk
           storage space.

        o  The codes are in the binary form easily interpreted by the
           computer (ANSI sequences use ASCII).

        o  The same file can be sent to callers who do or do not have
           the ability of interpreting ANSI codes - in the former case
           the codes are first translated to ANSI, in the latter they
           are ignored.

Because of lack of an appropriate name, Wynn temporarily named the codes
oANSI with the understanding that a better name was needed.

When I started working on my TinyTerm communications program, I had the
idea that if Opus-CBCS could send the "oANSI" codes directly over the phone
lines, it would speed up the communications considerably. A typical ANSI
sequence contains 4 times as many bytes as the codes developed by Wynn
Wagner.

A phone call to Wynn resulted in two things: 

        o  TinyTerm can interpret the "oANSI" codes and translate
           them to ANSI, then send them to stdout where they are
           converted to colors by ANSI.SYS.

        o  Opus-CBCS, starting with gamma version 1.10.iii, will
           send the codes without converting them to ANSI sequences.
           (It will still send ANSI codes to users without the proper
           terminal software.)

I took over the coding of the part of Opus handling the video codes. I
realized the codes were offering us much more power than just translating
them to ANSI escape sequences. I proposed to call the codes AVATAR, the
Advanced Video Attribute Terminal Assembler and Recreator. Wynn readily
accepted the new name.



                     The Two Levels of Avatar

Avatar is more than a video attribute controller. It is a protocol which,
if need be, can totally eliminate the interference of line noise. However,
this document is not concerned with the advanced topics of Avatar (which
no program is using as of this writing).

A full Avatar session with all its advanced features starts by exchanging
the AVINIT packets. The caller sends a packet which describes the video
capabilities of his/her system. It also contains the caller's name, password
and some other optional information. It also tells the BBS if the user is
calling in person or just emulating a BBS session with an Avatar terminal
program.

The called system (the BBS) replies to the AVINIT packet with a packet that
informs the user of his current status, e.g. you can stay till 16:30 GMT,
or you are denied access, or I am processing mail now but you can call back
at 10:43 GMT, etc.

Until such AVINIT packets are exchanged, only the Avatar commands that were
part of the original oANSI codes can be sent from the BBS to the caller.
The caller's term program should send no Avatar commands, with the exception
of function key codes, before the AVINIT packets are exchanged. This assures
that a BBS program which does not support full Avatar can still take
advantage of the faster transfer of video codes using Avatar as opposed to
ANSI escape sequences. It also permits the caller whose term program does
not support full Avatar but can interpret the basic codes to take advantage
of the term program's abilities.

The two levels of Avatar then are: a full session and a basic session. This
document is concerned with the BASIC Avatar session only. The full session
will be defined in a separate document.




                       Basic Avatar Commands


Before the AVINIT packets are exchanged, the BBS can send the basic Avatar
commands if so permitted by the user's choice, typically recorded in the
user datafile (e.g. USER.BBS). Because Avatar is window oriented, in a
basic session the full screen is considered the default window. Further,
the default color of the window is assumed to be 3 (cyan text on a black
background). All bytes are taken at their face value without escaping.
However, save for one exception described below, no basic Avatar code will
have the high bit set. Therefore, the term program should reset the high
bit of all bytes except as described below.

The basic commands are:

        <^L>    -       clear the current window and set current attribute
                        to default. In the basic session this means:
                        Clear the screen and set its attribute to 3.

        <^Y>    -       Read two bytes from the modem. Send the first one
                        to the screen as many times as the binary value
                        of the second one. This is the exception where
                        the two bytes may have their high bit set. Do
                        not reset it here!

        <^V> <^A> <attr> - Set the color attribute to <attr>. The default
                        attribute remains unchanged. However, all text
                        will be displayed in <attr> until the next ^V^A,
                        ^V^B, or ^L.

        <^V> <^B>   -   Turn the high bit of current attribute on. In
                        other words, turn blink on.

        <^V> <^C>   -   Move the cursor one line up. Do nothing, if you
                        already are at the top line of the current
                        window.

        <^V> <^D>   -   Move the cursor one line down. Do nothing if you
                        already are at the bottom line of the current
                        window.

        <^V> <^E>   -   Move the cursor one column to the left. Do nothing
                        if you already are at the leftmost column of the
                        current window.

        <^V> <^F>   -   Move the cursor one column to the right. Do nothing
                        if you already are at the rightmost column of the
                        current window.

        <^V> <^G>   -   Clear the rest of the line in the current window


                        using the current attribute (not to be confused
                        with the default attribute).

        <^V> <^H> <row> <col>   -   Move the cursor to the <row> <col>
                        position within the current window.


Comments:

Current attribute and default atribute are not necessarily the same.
Whenever the window is cleared by the <^L> command, the current attribute
is made equal to the default attribute. There is also another command to
make the current attribute equal to the default attribute. However, this
command is not a part of the basic Avatar command set and therefore cannot
be used before the AVINIT packets are exchanged.

Whatever characters are sent to the screen, they should be displayed using
the CURRENT attribute. There is an exception to this, but only after the
AVINIT packets have been exchanged.

The attribute byte is an eight-bit value. As basic Avatar can only transfer
7-bit commands, the high bit of the attribute byte can be set only by the
<^V> <^B> command. The <attr> byte of the <^V> <^A> <attr> command should
be AND-ed with 7F (hexadecimal). The colors set by the attribute byte are
the same as are the colors of the text mode of an IMB color graphics adapter.

That means the bits of the attribute byte have the following meaning:

     bit:         7   6   5   4   3   2   1   0
                  -   -   -   -   -   -   -   -
                  |   |       |   |           |
                  |   |       |   |           |
                  |   +---+---+   +-----+-----+
                  |       |             |
                  |       |             |
                  |       |
                  |       |         text color
                  |       |
                  |
                  |    background color
                  |

                blink

If the blink bit is set, the text is blinking, else it is not blinking.

The bits of background color can have values 0 - 7, the bits of the text
color can have values 0 - 15. The value indicates the following colors:

                 0      black
                 1      blue
                 2      green
                 3      cyan


                 4      red
                 5      magenta
                 6      brown
                 7      gray  (i.e. non-itense white)
                 8      dark gray
                 9      light blue
                10      light green
                11      light cyan
                12      light red
                13      light magenta
                14      yellow
                15      white (intense)

Colors 8 - 15 are the same as 0 - 7 but with high intensity.

Please note that these values are different from the numbers used by ANSI
escape codes.






                     The Function Key Codes



An Avatar capable BBS can accept function keys from the remote caller.
This feature is optional (for the term program) but highly recommended.

On an IBM (compatible) computer this means that if a caller hits a function
key (e.g., left arrow, page up, F7, insert, alt-H, etc.), the term program
should send two bytes to the Avatar capable BBS: A binary zero followed by
the keyboard scancode. Please note that control keys (^A, ^B, etc.) are not
function keys but have an ASCII value which is the only byte that should be
transfered.

There are two keys on the IBM keyboard that do have an ASCII value but also
offer a separate scan code. These are the gray-plus and the gray-minus. If
one of these keys is hit, treat it as a function key - send the binary zero
followed by the scan code. This way if the BBS treats them differently from a
regular plus and minus keys, the caller can take advantage of the keys.
On the other hand, BBS writers who do not want to assign the gray keys
a special value, should watch for their codes and treat them as a regular
plus and minus.

Systems that use a different keyboard layout (and scan codes) than IBM can
emulate IBM by declaring which keys are considered the arrows, f-keys, etc.
If you have the arrow keys, for example, but their scan codes are different,
still send the binary zero and the scan code that an IBM keyboard would
assign to that particular key. This should be transparent to the user.



There is an obvious problem here. All terminal programs I have seen use
function keys internally. A switch is needed so the user can decide whether
a function key is meant for the internal use of the term program or it
should be transfered to the BBS. Most but not all IBM clones have a scroll
lock key, some even have an LED indicator on it. The IBM programs could use
that as a switch to know what the user means by hitting a function key.
Since some compatibles do not have a scroll lock key (e.g. Tandy 1000), the
Avatar capable BBS should never expect the <shift> <F1> combination to be
transfered. That way the term program can use <shift> <F1> to switch between
the local and remote use of function keys if the scroll lock key is not
available.




                              Conclusion


This should about summarize the basic Avatar commands. I have written this
document one day before leaving for Fidocon '88 realizing it would be nice
to give the software developers (both of BBS's and term programs) something
before releasing the specs of the full Avatar implementation.

Here is also some sample C code. It assumes you have some low level
communications functions of your own. For the screen output it uses Turbo C
library, but you can use anything you want.*/


#include <conio.h>

int def_attr = 3;
int cur_attr = 3;
int lastline = 25;
int lastrow  = 80;

/* WARNING: This code has not been tested. It is just meant as an example  */

void pascal avatar()
{
 int c,i,j;

 switch (mgetchar())            /* Read a char from the modem */
  {
        case 12 :       textattr(cur_attr = def_attr);  /* ^L */
                        clrscr();
                        break;

        case 25 :       c = mgetchar();                 /* ^Y */
                        j = mgetchar();
                        for (i = 0; i < j; i++)
                                cprintf("%c",c);        /* print in color */
                        break;

        case 22 :       switch(mgetchar())              /* ^V */
                        {
                         case 1 : cur_attr = mgetchar() & 0x7f;
                                  textattr(cur_attr);
                                  break;

                         case 2 : cur_attr |= 0x80;
                                  textattr(cur_attr);
                                  break;

                         case 3 : if ((i = wherey()) > 1)
                                        gotoxy(wherex(),i - 1);
                                  break;

                         case 4 : if ((i = wherey()) < lastline)
                                        gotoxy(wherex(), i + 1);
                                  break;

                         case 5 : if ((i = wherex()) > 1)
                                        gotoxy(i - 1,wherey());
                                  break;

                         case 6 : if ((i = wherex()) < lastrow)
                                        gotoxy(i + 1,wherey());
                                  break;

                         case 7 : cleol();
                                  break;

                         case 8 : i = mgetchar();
                                  gotoxy(mgetchar(),i);
                        }
  }
}

