marc-leopold/app/components/BackgroundImageLoader.vue

<template>
  <div class="background-image-loader">
    <div class="background-container">
      <div class="background background-default"></div>
      <transition name="fade-fast"
      >
        <div v-if="loadedImageUrl !== null"
             class="background background-img background-blur"
             :style="backgroundBlurStyle"
        >
        </div>
      </transition>
      <transition name="fade"
                  @beforeEnter="handleBeforeEnter"
                  @afterLeave="handleAfterLeave"
      >
        <div class="background background-img"
             :key="loadedImageUrl"
             :style="backgroundStyle"
        >
        </div>
      </transition>
      <slot name="overlay">
      </slot>
    </div>
  </div>
</template>

<script>
import imageLoader from '~/mixins/imageLoader.js'

export default {
  mixins: [ imageLoader ],

  props: {
    imageUrl: {
      type: String,
      required: false,
      default: function () {
        return null
      }
    },
  },

  data () {
    return {
      loadedImageUrl: null,
      isInTransition: false,
      transitionTimeout: null,
    }
  },

  computed: {
    backgroundStyle () {
      let style = {}
      if (this.loadedImageUrl) {
        style.backgroundImage = `url(${this.loadedImageUrl})`
      }

      return style
    },

    backgroundBlurStyle () {
      let style = {}
      if (this.loadedImageUrl) {
        style.backgroundImage = `url(${this.loadedImageUrl})`
      }

      return style
    }
  },

  watch: {
    imageUrl () {
      if (!this.isInTransition && this.imageUrl) {
        this.setImage(this.imageUrl)
      }
    },
  },

  mounted () {
    this.setImage(this.imageUrl)
  },

  methods: {
    setImage(url) {
      if (url === null) { return }
      this.loadImage(url)
        .then(img => {
          this.loadedImageUrl = img.src
          this.$emit('imageLoaded', img)
        })
        .catch(err => {
          this.$emit('imageLoadError', err)
        })
    },

    handleBeforeEnter() {
      // TOOD get the actual value programatically
      // use ref and ref.style.transitionDuration or whatever
      let transitionDuration = 4000

      this.isInTransition = true

      clearTimeout(this.transitionTimeout)
      this.transitionTimeout = setTimeout(() => {
        this.isInTransition = false
        if (this.imageUrl !== this.loadedImageUrl) {
          this.setImage(this.imageUrl)
        }
      }, transitionDuration)
    },

    handleAfterLeave() {

    }
  },
}
</script>

<style lang="scss" scoped>

.background-image-loader {
  position: relative;
  width: 100%;
  height: 100%;
}

.background {
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  overflow: hidden;
}

.background-img {
  background-size: cover;
  background-position: center center;
  opacity: 1;
}

.background-default {
  $shadow-opacity: .6;
  $shadow-color: $color__neutral-100;
  background:
    linear-gradient(
      to right,
      rgba($shadow-color, $shadow-opacity),
      rgba($shadow-color, 0) 20%,
      rgba($shadow-color, 0) 80%,
      rgba($shadow-color, $shadow-opacity)
    ),
    linear-gradient(
      to bottom,
      rgba($shadow-color, $shadow-opacity),
      rgba($shadow-color, 0) 20%,
      rgba($shadow-color, 0) 80%,
      rgba($shadow-color, $shadow-opacity)
    ),
    linear-gradient(
      to top,
      $color__neutral-100,
      $color__neutral-300
  )
  ;
  overflow: hidden;
}

.background-blur {
  filter: blur(30px);
}

.fade {
  $timing: .7;
  &-enter-active {
    transition: opacity 4s * $timing 1s * $timing ease-in;
  }

  &-leave-active {
    transition: opacity 2s * $timing ease-out;
  }

  &-enter, &-leave-to {
    opacity: 0;
  }
}

.fade-fast {
  $timing: 1;
  &-enter-active {
    transition: opacity 3s * $timing ease-in;
    transition-delay: .2s;
  }

  &-enter {
    opacity: 0;
  }
}
</style>