swiper/src/components/core/update/updateSlidesProgress.js

Most modern mobile touch slider and framework with hardware accelerated transitions

import $ from '../../../utils/dom';

export default function (translate = (this && this.translate) || 0) {
  const swiper = this;
  const params = swiper.params;

  const { slides, rtlTranslate: rtl } = swiper;

  if (slides.length === 0) return;
  if (typeof slides[0].swiperSlideOffset === 'undefined') swiper.updateSlidesOffset();

  let offsetCenter = -translate;
  if (rtl) offsetCenter = translate;

  // Visible Slides
  slides.removeClass(params.slideVisibleClass);

  swiper.visibleSlidesIndexes = [];
  swiper.visibleSlides = [];

  for (let i = 0; i < slides.length; i += 1) {
    const slide = slides[i];
    const slideProgress = (
      (offsetCenter + (params.centeredSlides ? swiper.minTranslate() : 0)) - slide.swiperSlideOffset
    ) / (slide.swiperSlideSize + params.spaceBetween);
    if (params.watchSlidesVisibility || (params.centeredSlides && params.autoHeight)) {
      const slideBefore = -(offsetCenter - slide.swiperSlideOffset);
      const slideAfter = slideBefore + swiper.slidesSizesGrid[i];
      const isVisible = (slideBefore >= 0 && slideBefore < swiper.size - 1)
                || (slideAfter > 1 && slideAfter <= swiper.size)
                || (slideBefore <= 0 && slideAfter >= swiper.size);
      if (isVisible) {
        swiper.visibleSlides.push(slide);
        swiper.visibleSlidesIndexes.push(i);
        slides.eq(i).addClass(params.slideVisibleClass);
      }
    }
    slide.progress = rtl ? -slideProgress : slideProgress;
  }
  swiper.visibleSlides = $(swiper.visibleSlides);
}