Make loading encrypted images look snappier

res/css/_animations.scss

@@ -0,0 +1,55 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * React Transition Group animations are prefixed with 'mx_rtg--' so that we
+ * know they should not be used anywhere outside of React Transition Groups.
+*/
+
+.mx_rtg--fade-enter {
+    opacity: 0;
+}
+.mx_rtg--fade-enter-active {
+    opacity: 1;
+    transition: opacity 300ms ease;
+}
+.mx_rtg--fade-exit {
+    opacity: 1;
+}
+.mx_rtg--fade-exit-active {
+    opacity: 0;
+    transition: opacity 300ms ease;
+}
+
+
+@keyframes mx--anim-pulse {
+    0% { opacity: 1; }
+    50% { opacity: 0.7; }
+    100% { opacity: 1; }
+}
+
+
+@media (prefers-reduced-motion) {
+    @keyframes mx--anim-pulse {
+        // Override all keyframes in reduced-motion
+    }
+    .mx_rtg--fade-enter-active {
+        transition: none;
+    }
+    .mx_rtg--fade-exit-active {
+        transition: none;
+    }
+}

res/css/_common.scss

@@ -18,6 +18,7 @@ limitations under the License.
 
 @import "./_font-sizes.scss";
 @import "./_font-weights.scss";
+@import "./_animations.scss";
 
 $hover-transition: 0.08s cubic-bezier(.46, .03, .52, .96); // quadratic
 

res/css/views/messages/_MImageBody.scss

@@ -16,15 +16,24 @@ limitations under the License.
 
 $timelineImageBorderRadius: 4px;
 
+.mx_MImageBody_thumbnail--blurhash {
+    position: absolute;
+    left: 0;
+    top: 0;
+}
+
 .mx_MImageBody_thumbnail {
     object-fit: contain;
     border-radius: $timelineImageBorderRadius;
 
     display: flex;
     justify-content: center;
     align-items: center;
+    height: 100%;
+    width: 100%;
 
-    > div > canvas {
+    .mx_Blurhash > canvas {
+        animation: mx--anim-pulse 1.75s infinite cubic-bezier(.4, 0, .6, 1);
         border-radius: $timelineImageBorderRadius;
     }
 }

src/components/views/messages/MImageBody.tsx

@@ -25,12 +25,14 @@ import SettingsStore from "../../../settings/SettingsStore";
 import MatrixClientContext from "../../../contexts/MatrixClientContext";
 import InlineSpinner from '../elements/InlineSpinner';
 import { replaceableComponent } from "../../../utils/replaceableComponent";
-import { mediaFromContent } from "../../../customisations/Media";
+import { Media, mediaFromContent } from "../../../customisations/Media";
 import { BLURHASH_FIELD } from "../../../ContentMessages";
 import { IMediaEventContent } from '../../../customisations/models/IMediaEventContent';
 import ImageView from '../elements/ImageView';
 import { SyncState } from 'matrix-js-sdk/src/sync.api';
 import { IBodyProps } from "./IBodyProps";
+import classNames from 'classnames';
+import { CSSTransition, SwitchTransition } from 'react-transition-group';
 
 interface IState {
     decryptedUrl?: string;
@@ -157,19 +159,21 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
             // this is only used as a fallback in case content.info.w/h is missing
             loadedImageDimensions = { naturalWidth, naturalHeight };
         }
-
         this.setState({ imgLoaded: true, loadedImageDimensions });
     };
 
     protected getContentUrl(): string {
-        const media = mediaFromContent(this.props.mxEvent.getContent());
-        if (media.isEncrypted) {
+        if (this.media.isEncrypted) {
             return this.state.decryptedUrl;
         } else {
-            return media.srcHttp;
+            return this.media.srcHttp;
         }
     }
 
+    private get media(): Media {
+        return mediaFromContent(this.props.mxEvent.getContent());
+    }
+
     protected getThumbUrl(): string {
         // FIXME: we let images grow as wide as you like, rather than capped to 800x600.
         // So either we need to support custom timeline widths here, or reimpose the cap, otherwise the
@@ -225,7 +229,7 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
                     info.w > thumbWidth ||
                     info.h > thumbHeight
                 );
-                const isLargeFileSize = info.size > 1*1024*1024; // 1mb
+                const isLargeFileSize = info.size > 1 * 1024 * 1024; // 1mb
 
                 if (isLargeFileSize && isLargerThanThumbnail) {
                     // image is too large physically and bytewise to clutter our timeline so
@@ -374,23 +378,40 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
             gifLabel = <p className="mx_MImageBody_gifLabel">GIF</p>;
         }
 
+        const classes = classNames({
+            'mx_MImageBody_thumbnail': true,
+            'mx_MImageBody_thumbnail--blurhash': this.props.mxEvent.getContent().info[BLURHASH_FIELD],
+        });
+
+        // This has incredibly broken types.
+        const C = CSSTransition as any;
         const thumbnail = (
             <div className="mx_MImageBody_thumbnail_container" style={{ maxHeight: maxHeight, maxWidth: maxWidth, aspectRatio: `${infoWidth}/${infoHeight}` }}>
-                { showPlaceholder &&
-                    <div
-                        className="mx_MImageBody_thumbnail"
-                        style={{
-                            // Constrain width here so that spinner appears central to the loaded thumbnail
-                            maxWidth: `min(100%, ${infoWidth}px)`,
-                        }}
+                <SwitchTransition mode="out-in">
+                    <C
+                        classNames="mx_rtg--fade"
+                        key={`img-${showPlaceholder}`}
+                        timeout={300}
                     >
-                        { placeholder }
-                    </div>
-                }
+                        { /* This weirdly looking div is necessary here, otherwise SwitchTransition fails */ }
+                        <div>
+                            { showPlaceholder && <div
+                                className={classes}
+                                style={{
+                                    // Constrain width here so that spinner appears central to the loaded thumbnail
+                                    maxWidth: `min(100%, ${infoWidth}px)`,
+                                    maxHeight: maxHeight,
+                                    aspectRatio: `${infoWidth}/${infoHeight}`,
+                                }}
+                            >
+                                { placeholder }
+                            </div> }
+                        </div>
+                    </C>
+                </SwitchTransition>
 
                 <div style={{
-                    display: !showPlaceholder ? undefined : 'none',
-                    height: '100%', // Also force to size of a parent to prevent scroll-jumps (see above)
+                    height: '100%',
                 }}>
                     { img }
                     { gifLabel }
@@ -413,7 +434,7 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
     // Overidden by MStickerBody
     protected getPlaceholder(width: number, height: number): JSX.Element {
         const blurhash = this.props.mxEvent.getContent().info[BLURHASH_FIELD];
-        if (blurhash) return <Blurhash hash={blurhash} width={width} height={height} />;
+        if (blurhash) return <Blurhash className="mx_Blurhash" hash={blurhash} width={width} height={height} />;
         return (
             <InlineSpinner w={32} h={32} />
         );
@@ -455,10 +476,12 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
         const thumbnail = this.messageContent(contentUrl, thumbUrl, content);
         const fileBody = this.getFileBody();
 
-        return <div className="mx_MImageBody">
-            { thumbnail }
-            { fileBody }
-        </div>;
+        return (
+            <div className="mx_MImageBody">
+                { thumbnail }
+                { fileBody }
+            </div>
+        );
     }
 }