[Glitch] Center thumbnails on focus point

Port the display part of the following commits to glitch-soc:
* 90f12f2e5a
* b170627ceb
* 11697d6894
* 56eb5c3f34

app/javascript/flavours/glitch/components/media_gallery.js

@@ -147,6 +147,11 @@ class Item extends React.PureComponent {
       const srcSet = hasSize ? `${originalUrl} ${originalWidth}w, ${previewUrl} ${previewWidth}w` : null;
       const sizes  = hasSize ? `(min-width: 1025px) ${320 * (width / 100)}px, ${width}vw` : null;
 
+      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 = (
         <a
           className='media-gallery__item-thumbnail'
@@ -154,7 +159,14 @@ class Item extends React.PureComponent {
           onClick={this.handleClick}
           target='_blank'
         >
-          <img className={letterbox ? 'letterbox' : null} src={previewUrl} srcSet={srcSet} sizes={sizes} alt={attachment.get('description')} title={attachment.get('description')} />
+          <img
+            className={letterbox ? 'letterbox' : null}
+            src={previewUrl}
+            srcSet={srcSet}
+            sizes={sizes}
+            alt={attachment.get('description')}
+            title={attachment.get('description')}
+            style={{ objectPosition: `${x}% ${y}%` }} />
         </a>
       );
     } else if (attachment.get('type') === 'gifv') {
@@ -226,7 +238,7 @@ export default class MediaGallery extends React.PureComponent {
   }
 
   handleRef = (node) => {
-    if (node && this.isStandaloneEligible()) {
+    if (node /*&& this.isStandaloneEligible()*/) {
       // offsetWidth triggers a layout, so only calculate when we need to
       this.setState({
         width: node.offsetWidth,

app/javascript/flavours/glitch/features/video/index.js

@@ -29,7 +29,7 @@ const formatTime = secondsNum => {
   return (hours === '00' ? '' : `${hours}:`) + `${minutes}:${seconds}`;
 };
 
-const findElementPosition = el => {
+export const findElementPosition = el => {
   let box;
 
   if (el.getBoundingClientRect && el.parentNode) {
@@ -60,7 +60,7 @@ const findElementPosition = el => {
   };
 };
 
-const getPointerPosition = (el, event) => {
+export const getPointerPosition = (el, event) => {
   const position = {};
   const box = findElementPosition(el);
   const boxW = el.offsetWidth;
@@ -76,7 +76,7 @@ const getPointerPosition = (el, event) => {
     pageY = event.changedTouches[0].pageY;
   }
 
-  position.y = Math.max(0, Math.min(1, ((boxY - pageY) + boxH) / boxH));
+  position.y = Math.max(0, Math.min(1, (pageY - boxY) / boxH));
   position.x = Math.max(0, Math.min(1, (pageX - boxX) / boxW));
 
   return position;