Pull render animation frame logic into a helper class

src/utils/RenderDebouncer.ts

@@ -0,0 +1,50 @@
+import { ITerminal, IDisposable } from '../Interfaces';
+
+/**
+ * Debounces calls to render terminal rows using animation frames.
+ */
+export class RenderDebouncer implements IDisposable {
+  private _rowStart: number;
+  private _rowEnd: number;
+  private _animationFrame: number = null;
+
+  constructor(
+    private _terminal: ITerminal,
+    private _callback: (start: number, end: number) => void
+  ) {
+  }
+
+  public dispose(): void {
+    if (this._animationFrame) {
+      window.cancelAnimationFrame(this._animationFrame);
+      this._animationFrame = null;
+    }
+  }
+
+  public refresh(rowStart?: number, rowEnd?: number): void {
+    rowStart = rowStart || 0;
+    rowEnd = rowEnd || this._terminal.rows - 1;
+    this._rowStart = this._rowStart ? Math.min(this._rowStart, rowStart) : rowStart;
+    this._rowEnd = this._rowEnd ? Math.max(this._rowEnd, rowEnd) : rowEnd;
+
+    if (this._animationFrame) {
+      return;
+    }
+
+    this._animationFrame = window.requestAnimationFrame(() => this._innerRefresh());
+  }
+
+  private _innerRefresh(): void {
+    // Clamp values
+    this._rowStart = Math.max(this._rowStart, 0);
+    this._rowEnd = Math.min(this._rowEnd, this._terminal.rows - 1);
+
+    // Run render callback
+    this._callback(this._rowStart, this._rowEnd);
+
+    // Reset debouncer
+    this._rowStart = null;
+    this._rowEnd = null;
+    this._animationFrame = null;
+  }
+}