Focal points (#6520)

* Add focus param to media API, center thumbnails on focus point

* Add UI for setting a focal point

* Improve focal point icon on upload item

* Use focal point in upload preview

* Add focalPoint property to ActivityPub

* Don't show focal point button for non-image attachments

app/javascript/styles/mastodon/components.scss

@@ -433,6 +433,34 @@
       min-width: 40%;
       margin: 5px;
 
+      &__actions {
+        background: linear-gradient(180deg, rgba($base-shadow-color, 0.8) 0, rgba($base-shadow-color, 0.35) 80%, transparent);
+        display: flex;
+        align-items: flex-start;
+        justify-content: space-between;
+        opacity: 0;
+        transition: opacity .1s ease;
+
+        .icon-button {
+          flex: 0 1 auto;
+          color: $ui-secondary-color;
+          font-size: 14px;
+          font-weight: 500;
+          padding: 10px;
+          font-family: inherit;
+
+          &:hover,
+          &:focus,
+          &:active {
+            color: lighten($ui-secondary-color, 4%);
+          }
+        }
+
+        &.active {
+          opacity: 1;
+        }
+      }
+
       &-description {
         position: absolute;
         z-index: 2;
@@ -470,10 +498,6 @@
           opacity: 1;
         }
       }
-
-      .icon-button {
-        mix-blend-mode: difference;
-      }
     }
 
     .compose-form__upload-thumbnail {
@@ -481,8 +505,9 @@
       background-position: center;
       background-size: cover;
       background-repeat: no-repeat;
-      height: 100px;
+      height: 140px;
       width: 100%;
+      overflow: hidden;
     }
   }
 
@@ -4133,8 +4158,12 @@ a.status-card {
   &,
   img {
     width: 100%;
-    height: 100%;
+  }
+
+  img {
+    position: relative;
     object-fit: cover;
+    height: auto;
   }
 }
 
@@ -4842,3 +4871,31 @@ noscript {
     margin-bottom: 0;
   }
 }
+
+.focal-point {
+  position: relative;
+  cursor: pointer;
+  overflow: hidden;
+
+  &.dragging {
+    cursor: move;
+  }
+
+  &__reticle {
+    position: absolute;
+    width: 100px;
+    height: 100px;
+    transform: translate(-50%, -50%);
+    background: url('../images/reticle.png') no-repeat 0 0;
+    border-radius: 50%;
+    box-shadow: 0 0 0 9999em rgba($base-shadow-color, 0.35);
+  }
+
+  &__overlay {
+    position: absolute;
+    width: 100%;
+    height: 100%;
+    top: 0;
+    left: 0;
+  }
+}