lively.next Morph>>onMouseWheel (stopping scroll in windows and such)

foo.js

  onMouseWheel(evt) {
    var scrollTarget = evt.targetMorphs.find(ea => ea.isClip());
    if (this !== scrollTarget) return;
    var {deltaY, deltaX} = evt.domEvt,
        magnX = Math.abs(deltaX),
        magnY = Math.abs(deltaY);


    // This dance here is to avoid "overscroll", i.e. you scroll a clip morph
    // and it reaches it's boundary. Normally the clip morphs up the scene graph
    // would now be scrolled, e.g. the world, moving your view away from the morph
    // you are looking at. This is highly undesirable.

    var kind = "both directions";
    if (magnX <= 2 && magnY <= 2) kind = "tiny";
    else if (magnY / magnX <= 0.2) kind = "horizontal";
    else if (magnX / magnY <= 0.2) kind = "vertical";


    if (kind === "tiny") return;


    var {x: scrollX, y: scrollY} = this.scroll,
        newScrollTop = deltaY + scrollY,
        newScrollLeft = deltaX + scrollX,
        newScrollBottom = newScrollTop + this.height,
        newScrollRight = newScrollLeft + this.width,
        newScrollX, newScrollY;

    if (kind === "vertical" || kind === "both directions") {
      if (newScrollBottom >= this.scrollExtent.y) newScrollY = this.scrollExtent.y-1;
      else if (newScrollTop <= 0) newScrollY = 1;
      if (newScrollY !== undefined) {
        this.scroll = pt(scrollX, newScrollY);
        evt.stop();
      }

    } else if (kind === "horizontal" || kind === "both directions") {
      if (newScrollRight >= this.scrollExtent.x) newScrollX = this.scrollExtent.x-1;
      else if (newScrollLeft <= 0) newScrollX = 1;
      if (newScrollX !== undefined) {
        this.scroll = pt(newScrollX, scrollY);
        evt.stop();
      }
    }

    // Here we install a debouncer for letting the renderer know when it is
    // safe to update the DOM for scroll values.
    // See MorphAfterRenderHook in rendering/morphic-default.js and
    // https://github.com/LivelyKernel/lively.morphic/issues/88
    // for more info
    if (!evt.state.scroll.interactiveScrollInProgress) {
      var {promise: p, resolve} = promise.deferred();
      evt.state.scroll.interactiveScrollInProgress = p;
      p.debounce = fun.debounce(250, () => {
        evt.state.scroll.interactiveScrollInProgress = null;
        resolve();
      });
    }
    evt.state.scroll.interactiveScrollInProgress.debounce();
  }