serialize from the bottom of the terminal

addons/xterm-addon-serialize/src/SerializeAddon.api.ts

@@ -83,7 +83,7 @@ describe('SerializeAddon', () => {
       window.term.write(${util.inspect(lines.join('\r\n'))});
     `);
 
-    assert.equal(await page.evaluate(`serializeAddon.serialize(${halfRows});`), lines.slice(0, halfRows).join('\r\n'));
+    assert.equal(await page.evaluate(`serializeAddon.serialize(${halfRows});`), lines.slice(halfRows, 2 * halfRows).join('\r\n'));
   });
 
   it('serialize 0 rows of content', async function (): Promise<any> {

addons/xterm-addon-serialize/src/SerializeAddon.ts

@@ -5,6 +5,10 @@
 
 import { Terminal, ITerminalAddon } from 'xterm';
 
+function crop(value: number, from: number, to: number) {
+  return Math.max(from, Math.min(value, to))
+}
+
 export class SerializeAddon implements ITerminalAddon {
   private _terminal: Terminal | undefined;
 
@@ -19,13 +23,18 @@ export class SerializeAddon implements ITerminalAddon {
     if (!this._terminal) {
       throw new Error('Cannot use addon until it has been loaded');
     }
-    const buffer = this._terminal.buffer;
+    const terminalRows = this._terminal.rows;
-    const length = Math.max(0, Math.min((rows === undefined ? buffer.length : rows), buffer.length));
+    if (rows === undefined) {
-    const lines: string[] = new Array<string>(length);
+      rows = terminalRows;
+    }
+    rows = crop(rows, 0, terminalRows);
 
-    for (let i = 0; i < length; i++) {
+    const buffer = this._terminal.buffer;
+    const lines: string[] = new Array<string>(rows);
+
+    for (let i = terminalRows - rows; i < terminalRows; i++) {
       const line = buffer.getLine(i);
-      lines[i] = line ? line.translateToString() : '';
+      lines[i - terminalRows + rows] = line ? line.translateToString() : '';
     }
 
     return lines.join('\r\n');

addons/xterm-addon-serialize/typings/xterm-addon-serialize.d.ts

@@ -25,7 +25,7 @@ declare module 'xterm-addon-serialize' {
      * to restore the state. The cursor will also be positioned to the correct cell.
      * When restoring a terminal it is best to do before `Terminal.open` is called
      * to avoid wasting CPU cycles rendering incomplete frames.
-     * @param rows The number of rows to serialize, starting from the top of the
+     * @param rows The number of rows to serialize, starting from the bottom of the
      * terminal. This defaults to the number of rows in the viewport.
      */
     public serialize(rows?: number): string;