Function onWheel

src/interaction/createInsideZoom.ts:126–172

(e: WheelEvent)

  };

  const onWheel = (e: WheelEvent): void => {
    if (!enabled || disposed) return;

    const p = lastPointer;
    if (!p || !p.isInGrid) return;

    const plotWidthCss = p.plotWidthCss;
    const plotHeightCss = p.plotHeightCss;
    if (!(plotWidthCss > 0) || !(plotHeightCss > 0)) return;

    const deltaYCss = normalizeWheelDelta(e, plotHeightCss);
    const deltaXCss = normalizeWheelDeltaX(e, plotWidthCss);

    // Check if horizontal scroll is dominant (pan operation).
    if (Math.abs(deltaXCss) > Math.abs(deltaYCss) && deltaXCss !== 0) {
      const { start, end } = zoomState.getRange();
      const span = end - start;
      if (!Number.isFinite(span) || span === 0) return;

      // Convert horizontal scroll delta to percent pan.
      // Positive deltaX = scroll right = pan right (show earlier data).
      const deltaPct = (deltaXCss / plotWidthCss) * span;
      if (!Number.isFinite(deltaPct) || deltaPct === 0) return;

      e.preventDefault();
      zoomState.pan(deltaPct);
      return;
    }

    // Otherwise, proceed with vertical scroll zoom logic.
    if (deltaYCss === 0) return;

    const factor = wheelDeltaToZoomFactor(deltaYCss);
    if (!(factor > 1)) return;

    const { start, end } = zoomState.getRange();
    const span = end - start;
    if (!Number.isFinite(span) || span === 0) return;
    const r = clamp(p.gridX / plotWidthCss, 0, 1);
    const centerPct = clamp(start + r * span, 0, 100);

    // Only prevent default when we are actually consuming the wheel to zoom.
    e.preventDefault();

    if (deltaYCss < 0) zoomState.zoomIn(centerPct, factor);
    else zoomState.zoomOut(centerPct, factor);
  };

  const enable: InsideZoom['enable'] = () => {
    if (disposed || enabled) return;