added drag offset to findScrollTarget

Author: cameron-toy

packages/dragdrop/src/index.ts

@@ -410,7 +410,7 @@ class Drag implements IDisposable {
    */
   private _updateDragScroll(event: MouseEvent): void {
     // Find the scroll target under the mouse.
-    let target = Private.findScrollTarget(event);
+    let target = Private.findScrollTarget(event, this.dragOffsetX, this.dragOffsetY);
 
     // Bail if there is nothing to scroll.
     if (!this._scrollTarget && !target) {
@@ -830,17 +830,18 @@ namespace Private {
    * Find the drag scroll target under the mouse, if any.
    */
   export
-  function findScrollTarget(event: MouseEvent): IScrollTarget | null {
+  function findScrollTarget(event: MouseEvent, dragOffsetX: number, dragOffsetY: number): IScrollTarget | null {
     // Look up the client mouse position.
-    const x = event.clientX + drag.dragOffsetX;
-    const y = event.clientY + drag.dragOffsetY;
+    const x = event.clientX + dragOffsetX;
+    const y = event.clientY + dragOffsetY;
 
     // Get the element under the mouse.
     let element: Element | null = document.elementFromPoint(x, y);
 
     // Search for a scrollable target based on the mouse position.
     // The null assert in third clause of for-loop is required due to:
     // https://github.com/Microsoft/TypeScript/issues/14143
+
     for (; element; element = element!.parentElement) {
       // Ignore elements which are not marked as scrollable.
       let scrollable = element.hasAttribute('data-lm-dragscroll');