Add option to reduce motion (#5393)

* Add option to reduce motion

* Use HOC to wrap all Motion calls

* fix case-sensitive issue

* Avoid updating too frequently

* Get rid of unnecessary change to _simple_status.html.haml

1 files changed, 34 insertions, 0 deletions

diff --git a/app/javascript/mastodon/features/ui/util/optional_motion.js b/app/javascript/mastodon/features/ui/util/optional_motion.js
new file mode 100644
index 000000000..4276eeaa4
--- /dev/null
+++ b/app/javascript/mastodon/features/ui/util/optional_motion.js
@@ -0,0 +1,34 @@
+// Like react-motion's Motion, but checks to see if the user prefers
+// reduced motion and uses a cross-fade in those cases.
+
+import Motion from 'react-motion/lib/Motion';
+import { connect } from 'react-redux';
+
+const stylesToKeep = ['opacity', 'backgroundOpacity'];
+
+const extractValue = (value) => {
+  // This is either an object with a "val" property or it's a number
+  return (typeof value === 'object' && value && 'val' in value) ? value.val : value;
+};
+
+const mapStateToProps = (state, ownProps) => {
+  const reduceMotion = state.getIn(['meta', 'reduce_motion']);
+
+  if (reduceMotion) {
+    const { style, defaultStyle } = ownProps;
+
+    Object.keys(style).forEach(key => {
+      if (stylesToKeep.includes(key)) {
+        return;
+      }
+      // If it's setting an x or height or scale or some other value, we need
+      // to preserve the end-state value without actually animating it
+      style[key] = defaultStyle[key] = extractValue(style[key]);
+    });
+
+    return { style, defaultStyle };
+  }
+  return {};
+};
+
+export default connect(mapStateToProps)(Motion);