Add CharMeasure util class

src/utils/CharMeasure.ts

@@ -0,0 +1,52 @@
+/**
+ * @module xterm/utils/CharMeasure
+ * @license MIT
+ */
+
+import { EventEmitter } from '../EventEmitter.js';
+
+/**
+ * Utility class that measures the size of a character.
+ */
+export class CharMeasure extends EventEmitter {
+  private _parentElement: HTMLElement;
+  private _measureElement: HTMLElement;
+  private _width: number;
+  private _height: number;
+
+  constructor(parentElement: HTMLElement) {
+    super();
+    this._parentElement = parentElement;
+  }
+
+  public get width(): number {
+    return this._width;
+  }
+
+  public get height(): number {
+    return this._height;
+  }
+
+  public measure(): void {
+    const oldWidth = this._width;
+    const oldHeight = this._height;
+
+    if (!this._measureElement) {
+      this._measureElement = document.createElement('span');
+      this._measureElement.style.position = 'absolute';
+      this._measureElement.style.top = '0';
+      this._measureElement.style.left = '-9999em';
+      this._measureElement.textContent = 'W';
+    }
+
+    this._parentElement.appendChild(this._measureElement);
+    const geometry = this._measureElement.getBoundingClientRect();
+    this._width = geometry.width;
+    this._height = geometry.height;
+    this._parentElement.removeChild(this._measureElement);
+
+    if (this._width !== oldWidth || this._height !== oldHeight) {
+      this.emit('charsizechanged');
+    }
+  }
+}