Use preview image in <ImageLoader /> to provide immediate visual feedback (#3595)

before the full-size image is loaded

app/javascript/mastodon/features/ui/components/image_loader.js

@@ -5,6 +5,9 @@ class ImageLoader extends React.PureComponent {
 
   static propTypes = {
     src: PropTypes.string.isRequired,
+    previewSrc: PropTypes.string.isRequired,
+    width: PropTypes.number.isRequired,
+    height: PropTypes.number.isRequired,
   }
 
   state = {
@@ -13,31 +16,45 @@ class ImageLoader extends React.PureComponent {
   }
 
   componentWillMount() {
-    this.loadImage(this.props.src);
+    this._loadImage(this.props.src);
   }
 
   componentWillReceiveProps(props) {
-    this.loadImage(props.src);
+    this._loadImage(props.src);
   }
 
-  loadImage(src) {
+  _loadImage(src) {
     const image = new Image();
+
     image.onerror = () => this.setState({ loading: false, error: true });
-    image.onload = () => this.setState({ loading: false, error: false });
+    image.onload  = () => this.setState({ loading: false, error: false });
+
     image.src = src;
-    this.lastSrc = src;
+
     this.setState({ loading: true });
   }
 
   render() {
-    const { src } = this.props;
+    const { src, previewSrc, width, height } = this.props;
     const { loading, error } = this.state;
 
-    // TODO: handle image error state
+    return (
+      <div className='image-loader'>
+        <img // eslint-disable-line jsx-a11y/img-has-alt
+          className='image-loader__img'
+          src={src}
+          width={width}
+          height={height}
+        />
 
-    const imageClass = `image-loader__img ${loading ? 'image-loader__img-loading' : ''}`;
-
-    return <img className={imageClass} src={src} />; // eslint-disable-line jsx-a11y/img-has-alt
+        {loading &&
+          <img // eslint-disable-line jsx-a11y/img-has-alt
+            src={previewSrc}
+            className='image-loader__preview-img'
+          />
+        }
+      </div>
+    );
   }
 
 }

app/javascript/mastodon/features/ui/components/media_modal.js

@@ -73,7 +73,7 @@ class MediaModal extends ImmutablePureComponent {
     }
 
     if (attachment.get('type') === 'image') {
-      content = <ImageLoader src={url} />;
+      content = <ImageLoader previewSrc={attachment.get('preview_url')} src={url} width={attachment.getIn(['meta', 'original', 'width'])} height={attachment.getIn(['meta', 'original', 'height'])} />;
     } else if (attachment.get('type') === 'gifv') {
       content = <ExtendedVideoPlayer src={url} muted controls={false} />;
     }

app/javascript/styles/components.scss

@@ -1137,13 +1137,22 @@
   }
 }
 
-.image-loader__img {
-  transition: opacity 0.3s linear;
-  opacity: 1;
+.image-loader {
+  position: relative;
 }
 
-.image-loader__img-loading {
-  opacity: 0.7;
+.image-loader__preview-img {
+  position: absolute;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  filter: blur(2px);
+}
+
+.media-modal img.image-loader__preview-img {
+  width: 100%;
+  height: 100%;
 }
 
 .navigation-bar {
@@ -2951,6 +2960,8 @@ button.icon-button.active i.fa-retweet {
   video {
     max-width: 80vw;
     max-height: 80vh;
+    width: auto;
+    height: auto;
   }
 
   img {