Generates a value between 0-1 given the current pointer position in relation
to the MultiSlider's position, and triggers output.
@instance
@memberof MultiSlider
@param {PointerEvent} e - The pointer event to be processed.
function processPointerPosition(e) {
    var prevValue = this.value,
        sliderNum = void 0;

    if (this.style === 'horizontal') {
      sliderNum = Math.floor(e.clientY / this.rect.height / (1 / this.count));
      this.__value[sliderNum] = (e.clientX - this.rect.left) / this.rect.width;
    } else {
      sliderNum = Math.floor(e.clientX / this.rect.width / (1 / this.count));
      this.__value[sliderNum] = 1 - (e.clientY - this.rect.top) / this.rect.height;
    }

    for (var i = 0; i < this.count; i++) {
      if (this.__value[i] > 1) this.__value[i] = 1;
      if (this.__value[i] < 0) this.__value[i] = 0;
    }

    var shouldDraw = this.output();

    if (shouldDraw) this.draw();
  }