added scroll bubbling on wheel and touch move events

src/browser/Types.d.ts

@@ -37,9 +37,9 @@ export interface IViewport extends IDisposable {
   scrollBarWidth: number;
   syncScrollArea(): void;
   getLinesScrolled(ev: WheelEvent): number;
-  onWheel(ev: WheelEvent): void;
+  onWheel(ev: WheelEvent): boolean;
   onTouchStart(ev: TouchEvent): void;
-  onTouchMove(ev: TouchEvent): void;
+  onTouchMove(ev: TouchEvent): boolean;
   onThemeChange(colors: IColorSet): void;
 }
 

src/browser/Viewport.ts

@@ -152,20 +152,34 @@ export class Viewport extends Disposable implements IViewport {
     this._scrollLines(diff, true);
   }
 
+
+  private _bubbleScroll(amount: number): boolean {
+    const scrollPosFromTop = this._viewportElement.scrollTop + this._lastRecordedViewportHeight;
+    if ((amount < 0 && this._viewportElement.scrollTop !== 0) ||
+    (amount > 0 &&  scrollPosFromTop < this._lastRecordedBufferHeight)) {
+        return false;
+    }
+    return true;
+  }
+
   /**
    * Handles mouse wheel events by adjusting the viewport's scrollTop and delegating the actual
    * scrolling to `onScroll`, this event needs to be attached manually by the consumer of
    * `Viewport`.
    * @param ev The mouse wheel event.
    */
-  public onWheel(ev: WheelEvent): void {
+  public onWheel(ev: WheelEvent): boolean {
     const amount = this._getPixelsScrolled(ev);
     if (amount === 0) {
-      return;
+      return false;
     }
     this._viewportElement.scrollTop += amount;
     // Prevent the page from scrolling when the terminal scrolls
-    ev.preventDefault();
+    const shouldBubbleEvent = this._bubbleScroll(amount);
+    if (!shouldBubbleEvent && ev.cancelable) {
+      ev.preventDefault();
+    }
+    return shouldBubbleEvent;
   }
 
   private _getPixelsScrolled(ev: WheelEvent): number {
@@ -220,13 +234,17 @@ export class Viewport extends Disposable implements IViewport {
    * Handles the touchmove event, scrolling the viewport if the position shifted.
    * @param ev The touch event.
    */
-  public onTouchMove(ev: TouchEvent): void {
+  public onTouchMove(ev: TouchEvent): boolean {
     const deltaY = this._lastTouchY - ev.touches[0].pageY;
     this._lastTouchY = ev.touches[0].pageY;
     if (deltaY === 0) {
-      return;
+      return false;
     }
     this._viewportElement.scrollTop += deltaY;
-    ev.preventDefault();
+    const shouldBubbleEvent = this._bubbleScroll(deltaY);
+    if (!shouldBubbleEvent && ev.cancelable) {
+      ev.preventDefault();
+    }
+    return shouldBubbleEvent;
   }
 }