ANSI Cursor Control from Forth

When lacking a bit-mapped graphics interface, one old standby is ANSI cursor control, which allows 8 colors, with cursor positioning assuming a monospace font. It could allow you to do limited graphics and forms over a UART connection, e.g., the serial connection to a microcontroller.

An entertaining rabbit trail: Here is Emacs running the pong game in an X11 window (i.e., normal graphics):

But if you run Emacs in no-window mode (i.e., “terminal” mode) it looks like it falls back to control codes (ANSI escape codes…?)

Emacs was designed originally to be run in terminal environments which used control codes — bit-mapped graphics were later grafted on to Emacs. This allows Emacs to be run from a Gnu/Linux virtual console (e.g., CTRL-ALT-F2).

Anyway, here is a Forth interface to some of the ANSI escape codes, specifically line,column cursor positioning, and setting a graphics mode (character attributes like color and bold/underline).

\ Copyright 2020 Christopher Howard

\ ansi-cursor.fs

\ Licensed under the Apache License, Version 2.0 (the "License");
\ you may not use this file except in compliance with the License.
\ You may obtain a copy of the License at

\     http://www.apache.org/licenses/LICENSE-2.0

\ Unless required by applicable law or agreed to in writing, software
\ distributed under the License is distributed on an "AS IS" BASIS,
\ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
\ See the License for the specific language governing permissions and
\ limitations under the License.

\ http://ascii-table.com/ansi-escape-sequences.php

\ GFX mode values

30 constant black-fg
31 constant red-fg
32 constant green-fg
33 constant yellow-fg
34 constant blue-fg
35 constant magenta-fg
36 constant cyan-fg
37 constant white-fg

40 constant black-bg
41 constant red-bg
42 constant green-bg
43 constant yellow-bg
44 constant blue-bg
45 constant magenta-bg
46 constant cyan-bg
47 constant white-bg

0 constant attributes-off
1 constant bold
4 constant underscore
5 constant blink
7 constant reverse
8 constant concealed

: <esc> 0x1b emit ;

: <[> [char] [ emit ;

: .| abs 0 <# #s #> type ;

: <;> [char] ; emit ;

: position-cursor ( line col -- ) <esc> <[> swap .| <;> .| [char] H emit ;

: erase-display <esc> <[> 2 .| [char] J emit ;

: set-gfx-mode ( gfx-mode-value -- )
    <esc> <[> .| [char] m emit ;

And demo example code:

\ Copyright 2020 Christopher Howard

\ demo.fs

\ Licensed under the Apache License, Version 2.0 (the "License");
\ you may not use this file except in compliance with the License.
\ You may obtain a copy of the License at

\     http://www.apache.org/licenses/LICENSE-2.0

\ Unless required by applicable law or agreed to in writing, software
\ distributed under the License is distributed on an "AS IS" BASIS,
\ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
\ See the License for the specific language governing permissions and
\ limitations under the License.

require ansi-cursor.fs

: exp-scale ( n prescaled-range scaled-range -- n )
    rot dup * * swap dup * / ;

: cab-dist ( x y xc yc -- n ) 2 pick - abs >r swap drop - abs r> + ;

: demo-scale ( x y xc yx unscaled-range )
    >r cab-dist r> 8 exp-scale 7 min ;

: demo attributes-off set-gfx-mode erase-display
    80 0 do
        40 0 do
            i j 2dup position-cursor
            20 40 70 demo-scale black-bg + set-gfx-mode
            space
        loop
    loop
    attributes-off set-gfx-mode
    20 31 position-cursor ." * ansi-cursor demo *"
    40 0 position-cursor
;