Function zoom

src/components/utils/panzoom.js:286–308

(
    toScale,
    zoomOptions,
    focal
  )

  }

  function zoom(
    toScale,
    zoomOptions,
    focal
  ) {
    const result = constrainScale(toScale, zoomOptions)
    const zoomScale = result.scale
    const zoomOpts = result.opts
    if (scale !== zoomScale) {
      scale = zoomScale
      let toX = x
      let toY = y
      if (focal) {
        const focalX = focal.x || 0
        const focalY = focal.y || 0
        const diffScale = zoomScale / scale
        toX = focalX - (focalX - x) * diffScale
        toY = focalY - (focalY - y) * diffScale
      }
      return pan(toX, toY, zoomOpts, zoomOptions.originalEvent)
    }
    return { x, y, scale, isSVG: isSVGElement(elem), originalEvent: zoomOptions.originalEvent }
  }

  function zoomIn(zoomOptions) {
    zoom(scale + options.step, zoomOptions)