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80 lines
2.3 KiB
80 lines
2.3 KiB
<div class="Box fold">
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<h2>Alternate Character Sets</h2>
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<div class="Row v">
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<p>
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ESPTerm implements Alternate Character Sets as a way to print box drawing characters
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and special symbols. A character set can change what each received ASCII character
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is printed as on the screen (eg. "{" is "π" in codepage `0`). The implementation is based
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on the original VT devices.
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</p>
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<p>
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Since ESPTerm also supports UTF-8, this feature is the most useful for applications
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which can't print UTF-8 or already use alternate character sets for historical reasons.
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</p>
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<h3>Supported codepages</h3>
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<ul>
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<li>`B` - US ASCII (default)</li>
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<li>`A` - UK ASCII: # replaced with £</li>
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<li>`0` - Symbols and basic line drawing (standard DEC alternate character set)</li>
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<li>`1` - Symbols and advanced line drawing (based on DOS codepage 437, ESPTerm specific)</li>
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</ul>
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<p>
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All codepages use codes 32-127, 32 being space. A character with no entry in the active codepage
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stays unchanged.
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</p>
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<?php
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$codepages = load_esp_charsets();
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foreach($codepages as $name => $cp) {
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echo "<h4>Codepage `$name`</h4>\n";
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echo '<div class="charset">';
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foreach($cp as $point) {
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$dis = $point[1]==$point[2]?' class="none"' : '';
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echo "<div$dis><span>$point[0]</span><span>$point[1]</span><span>$point[2]</span></div>";
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}
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echo '</div>';
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}
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?>
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<h3>Switching commands</h3>
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<p>
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There are two character set slots, G0 and G1.
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Those slots are selected as active using ASCII codes Shift In and Shift Out (those originally served for shifting
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a red-black typewriter tape). Often only G0 is used for simplicity.
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</p>
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<p>
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Each slot (G0 and G1) can have a different codepage assigned. G0 and G1 and the active slot number are
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saved and restored with the cursor and cleared with a screen reset (<code>\ec</code>).
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</p>
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<p>The following commands are used:</p>
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<table class="ansiref w100">
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<thead><tr><th>Code</th><th>Meaning</th></tr></thead>
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<tbody>
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<tr>
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<td>`\e(<i>x</i>`</td>
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<td>Set G0 = codepage <i>x</i></td>
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</tr>
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<tr>
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<td>`\e)<i>x</i>`</td>
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<td>Set G1 = codepage <i>x</i></td>
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</tr>
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<tr>
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<td>_SO_ (14)</td>
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<td>Activate G0</td>
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</tr>
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<tr>
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<td>_SI_ (15)</td>
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<td>Activate G1</td>
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</tr>
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</table>
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</div>
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</div>
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