Alternate Character Sets

ESPTerm implements Alternate Character Sets as a way to print box drawing characters and special symbols. A character set can change what each received ASCII character is printed as on the screen (eg. "{" is "π" in codepage `0`). The implementation is based on the original VT devices.

Since ESPTerm also supports UTF-8, this feature is the most useful for applications which can't print UTF-8 or already use alternate character sets for historical reasons.

Supported codepages

`B` - US ASCII (default)
`A` - UK ASCII: # replaced with £
`0` - Symbols and basic line drawing (standard DEC alternate character set)
`1` - Symbols and advanced line drawing (based on DOS codepage 437, ESPTerm specific)

All codepages use codes 32-127, 32 being space. A character with no entry in the active codepage stays unchanged.

$cp) { echo "

Codepage `$name`

\n"; echo '

'; foreach($cp as $point) { $dis = $point[1]==$point[2]?' class="none"' : ''; echo "$point[0]$point[1]$point[2]

"; } echo '

'; } ?>

Switching commands

There are two character set slots, G0 and G1. Those slots are selected as active using ASCII codes Shift In and Shift Out (those originally served for shifting a red-black typewriter tape). Often only G0 is used for simplicity.

Each slot (G0 and G1) can have a different codepage assigned. G0 and G1 and the active slot number are saved and restored with the cursor and cleared with a screen reset (\ec).

The following commands are used:

Code	Meaning
`\e(x`	Set G0 = codepage x
`\e)x`	Set G1 = codepage x
_SO_ (14)	Activate G0
_SI_ (15)	Activate G1