mastodon/app/javascript/mastodon/features/account_gallery/components/media_item.js

import React from 'react';
import PropTypes from 'prop-types';
import ImmutablePropTypes from 'react-immutable-proptypes';
import ImmutablePureComponent from 'react-immutable-pure-component';
import { autoPlayGif, displayMedia } from 'mastodon/initial_state';
import classNames from 'classnames';
import { decode } from 'blurhash';
import { isIOS } from 'mastodon/is_mobile';

export default class MediaItem extends ImmutablePureComponent {

  static propTypes = {
    attachment: ImmutablePropTypes.map.isRequired,
    displayWidth: PropTypes.number.isRequired,
    onOpenMedia: PropTypes.func.isRequired,
  };

  state = {
    visible: displayMedia !== 'hide_all' && !this.props.attachment.getIn(['status', 'sensitive']) || displayMedia === 'show_all',
    loaded: false,
  };

  componentDidMount () {
    if (this.props.attachment.get('blurhash')) {
      this._decode();
    }
  }

  componentDidUpdate (prevProps) {
    if (prevProps.attachment.get('blurhash') !== this.props.attachment.get('blurhash') && this.props.attachment.get('blurhash')) {
      this._decode();
    }
  }

  _decode () {
    const hash   = this.props.attachment.get('blurhash');
    const pixels = decode(hash, 32, 32);

    if (pixels) {
      const ctx       = this.canvas.getContext('2d');
      const imageData = new ImageData(pixels, 32, 32);

      ctx.putImageData(imageData, 0, 0);
    }
  }

  setCanvasRef = c => {
    this.canvas = c;
  }

  handleImageLoad = () => {
    this.setState({ loaded: true });
  }

  handleMouseEnter = e => {
    if (this.hoverToPlay()) {
      e.target.play();
    }
  }

  handleMouseLeave = e => {
    if (this.hoverToPlay()) {
      e.target.pause();
      e.target.currentTime = 0;
    }
  }

  hoverToPlay () {
    return !autoPlayGif && ['gifv', 'video'].indexOf(this.props.attachment.get('type')) !== -1;
  }

  handleClick = e => {
    if (e.button === 0 && !(e.ctrlKey || e.metaKey)) {
      e.preventDefault();

      if (this.state.visible) {
        this.props.onOpenMedia(this.props.attachment);
      } else {
        this.setState({ visible: true });
      }
    }
  }

  render () {
    const { attachment, displayWidth } = this.props;
    const { visible, loaded } = this.state;

    const width  = `${Math.floor((displayWidth - 4) / 3) - 4}px`;
    const height = width;
    const status = attachment.get('status');

    let thumbnail = '';

    if (attachment.get('type') === 'unknown') {
      // Skip
    } else if (attachment.get('type') === 'image') {
      const focusX = attachment.getIn(['meta', 'focus', 'x']) || 0;
      const focusY = attachment.getIn(['meta', 'focus', 'y']) || 0;
      const x      = ((focusX /  2) + .5) * 100;
      const y      = ((focusY / -2) + .5) * 100;

      thumbnail = (
        <img
          src={attachment.get('preview_url')}
          alt={attachment.get('description')}
          title={attachment.get('description')}
          style={{ objectPosition: `${x}% ${y}%` }}
          onLoad={this.handleImageLoad}
        />
      );
    } else if (['gifv', 'video'].indexOf(attachment.get('type')) !== -1) {
      const autoPlay = !isIOS() && autoPlayGif;

      thumbnail = (
        <div className={classNames('media-gallery__gifv', { autoplay: autoPlay })}>
          <video
            className='media-gallery__item-gifv-thumbnail'
            aria-label={attachment.get('description')}
            title={attachment.get('description')}
            role='application'
            src={attachment.get('url')}
            onMouseEnter={this.handleMouseEnter}
            onMouseLeave={this.handleMouseLeave}
            autoPlay={autoPlay}
            loop
            muted
          />

          <span className='media-gallery__gifv__label'>GIF</span>
        </div>
      );
    }

    return (
      <div className='account-gallery__item' style={{ width, height }}>
        <a className='media-gallery__item-thumbnail' href={status.get('url')} target='_blank' onClick={this.handleClick}>
          <canvas width={32} height={32} ref={this.setCanvasRef} className={classNames('media-gallery__preview', { 'media-gallery__preview--hidden': visible && loaded })} />
          {visible && thumbnail}
        </a>
      </div>
    );
  }

}