Cache the tinted SVGs for MFileBody as data URLs (#559)

* Use a list of callbacks for things that need tinting.

Rather than gutwrenching the internals of TintableSVG inside the Tinter.

* Share a data: url for the tinted download svg in MFileBody

* Check image exists before tinting

* Add comments

* Use fetch+DomParser rather than XMLHttpRequest

* Remove comment about XMLHttpRequest

src/Tinter.js

@@ -153,7 +153,25 @@ function rgbToHex(rgb) {
     return '#' + (0x1000000 + val).toString(16).slice(1)
 }
 
+// List of functions to call when the tint changes.
+const tintables = [];
+
 module.exports = {
+    /**
+     * Register a callback to fire when the tint changes.
+     * This is used to rewrite the tintable SVGs with the new tint.
+     *
+     * It's not possible to unregister a tintable callback. So this can only be
+     * used to register a static callback. If a set of tintables will change
+     * over time then the best bet is to register a single callback for the
+     * entire set.
+     *
+     * @param {Function} tintable Function to call when the tint changes.
+     */
+    registerTintable : function(tintable) {
+        tintables.push(tintable);
+    },
+
     tint: function(primaryColor, secondaryColor, tertiaryColor) {
 
         if (!cached) {
@@ -201,12 +219,9 @@ module.exports = {
 
         // tell all the SVGs to go fix themselves up
         // we don't do this as a dispatch otherwise it will visually lag
-        var TintableSvg = sdk.getComponent("elements.TintableSvg");
-        if (TintableSvg.mounts) {
-            Object.keys(TintableSvg.mounts).forEach((id) => {
-                TintableSvg.mounts[id].tint();
+        tintables.forEach(function(tintable) {
+            tintable();
         });
-        }
     },
 
     // XXX: we could just move this all into TintableSvg, but as it's so similar
@@ -265,5 +280,5 @@ module.exports = {
             svgFixup.node.setAttribute(svgFixup.attr, colors[svgFixup.index]);
         }
         if (DEBUG) console.log("applySvgFixups end");
-    },
+    }
 };

src/components/views/elements/TintableSvg.js

@@ -74,4 +74,13 @@ var TintableSvg = React.createClass({
     }
 });
 
+// Register with the Tinter so that we will be told if the tint changes
+Tinter.registerTintable(function() {
+    if (TintableSvg.mounts) {
+        Object.keys(TintableSvg.mounts).forEach((id) => {
+            TintableSvg.mounts[id].tint();
+        });
+    }
+});
+
 module.exports = TintableSvg;

src/components/views/messages/MFileBody.js

@@ -21,7 +21,42 @@ import filesize from 'filesize';
 import MatrixClientPeg from '../../../MatrixClientPeg';
 import sdk from '../../../index';
 import {decryptFile} from '../../../utils/DecryptFile';
+import Tinter from '../../../Tinter';
+import 'isomorphic-fetch';
+import q from 'q';
 
+// A cached tinted copy of "img/download.svg"
+var tintedDownloadImageURL;
+// Track a list of mounted MFileBody instances so that we can update
+// the "img/download.svg" when the tint changes.
+var nextMountId = 0;
+const mounts = {};
+
+/**
+ * Updates the tinted copy of "img/download.svg" when the tint changes.
+ */
+function updateTintedDownloadImage() {
+    // Download the svg as an XML document.
+    // We could cache the XML response here, but since the tint rarely changes
+    // it's probably not worth it.
+    q(fetch("img/download.svg")).then(function(response) {
+        return response.text();
+    }).then(function(svgText) {
+        const svg = new DOMParser().parseFromString(svgText, "image/svg+xml");
+        // Apply the fixups to the XML.
+        const fixups = Tinter.calcSvgFixups([{contentDocument: svg}]);
+        Tinter.applySvgFixups(fixups);
+        // Encoded the fixed up SVG as a data URL.
+        const svgString = new XMLSerializer().serializeToString(svg);
+        tintedDownloadImageURL = "data:image/svg+xml;base64," + window.btoa(svgString);
+        // Notify each mounted MFileBody that the URL has changed.
+        Object.keys(mounts).forEach(function(id) {
+            mounts[id].tint();
+        });
+    }).done();
+}
+
+Tinter.registerTintable(updateTintedDownloadImage);
 
 module.exports = React.createClass({
     displayName: 'MFileBody',
@@ -70,6 +105,12 @@ module.exports = React.createClass({
     },
 
     componentDidMount: function() {
+        // Add this to the list of mounted components to receive notifications
+        // when the tint changes.
+        this.id = nextMountId++;
+        mounts[this.id] = this;
+        this.tint();
+        // Check whether we need to decrypt the file content.
         const content = this.props.mxEvent.getContent();
         if (content.file !== undefined && this.state.decryptedUrl === null) {
             decryptFile(content.file).done((url) => {
@@ -84,12 +125,23 @@ module.exports = React.createClass({
         }
     },
 
+    componentWillUnmount: function() {
+        // Remove this from the list of mounted components
+        delete mounts[this.id];
+    },
+
+    tint: function() {
+        // Update our tinted copy of "img/download.svg"
+        if (this.refs.downloadImage) {
+            this.refs.downloadImage.src = tintedDownloadImageURL;
+        }
+    },
+
     render: function() {
         const content = this.props.mxEvent.getContent();
 
         const text = this.presentableTextForFile(content);
 
-        var TintableSvg = sdk.getComponent("elements.TintableSvg");
         if (content.file !== undefined && this.state.decryptedUrl === null) {
 
             // Need to decrypt the attachment
@@ -155,7 +207,7 @@ module.exports = React.createClass({
                     <span className="mx_MFileBody">
                         <div className="mx_MImageBody_download">
                             <a href={contentUrl} target="_blank" rel="noopener" download={downloadAttr}>
-                                <TintableSvg src="img/download.svg" width="12" height="14"/>
+                                <img src={tintedDownloadImageURL} width="12" height="14" ref="downloadImage"/>
                                 Download {text}
                             </a>
                         </div>