Added content from old ESPTerm repo @ b8ed46cbea0b88730a2a6bad8375790158110910

2017-09-09 19:13:21 +02:00
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+<div class="Box fold">
+	<h2>Alternate Character Sets</h2>
+
+	<div class="Row v">
+		<p>
+			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.
+		</p>
+
+		<p>
+			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.
+		</p>
+
+		<h3>Supported codepages</h3>
+
+		<ul>
+			<li>`B` - US ASCII (default)</li>
+			<li>`A` - UK ASCII: # replaced with £</li>
+			<li>`0` - Symbols and basic line drawing (standard DEC alternate character set)</li>
+			<li>`1` - Symbols and advanced line drawing (based on DOS codepage 437, ESPTerm specific)</li>
+		</ul>
+
+		<p>
+			All codepages use codes 32-127, 32 being space. A character with no entry in the active codepage
+			stays unchanged.
+		</p>
+
+		<?php
+			$codepages = load_esp_charsets();
+			foreach($codepages as $name => $cp) {
+				echo "<h4>Codepage `$name`</h4>\n";
+				echo '<div class="charset">';
+				foreach($cp as $point) {
+					$dis = $point[1]==$point[2]?' class="none"' : '';
+					echo "<div$dis><span>$point[0]</span><span>$point[1]</span><span>$point[2]</span></div>";
+				}
+				echo '</div>';
+			}
+		?>
+
+		<h3>Switching commands</h3>
+
+		<p>
+			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.
+		</p>
+
+		<p>
+			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 (<code>\ec</code>).
+		</p>
+
+		<p>The following commands are used:</p>
+
+		<table class="ansiref w100">
+			<thead><tr><th>Code</th><th>Meaning</th></tr></thead>
+			<tbody>
+			<tr>
+				<td>`\e(<i>x</i>`</td>
+				<td>Set G0 = codepage <i>x</i></td>
+			</tr>
+			<tr>
+				<td>`\e)<i>x</i>`</td>
+				<td>Set G1 = codepage <i>x</i></td>
+			</tr>
+			<tr>
+				<td>_SO_ (14)</td>
+				<td>Activate G0</td>
+			</tr>
+			<tr>
+				<td>_SI_ (15)</td>
+				<td>Activate G1</td>
+			</tr>
+		</table>
+	</div>
+</div>