From c013e49192f7ab4f9eb2494edaac35e7c9bf434b Mon Sep 17 00:00:00 2001
From: Niklas von Hertzen <niklasvh@gmail.com>
Date: Sun, 3 Sep 2017 18:20:12 +0800
Subject: [PATCH] Only use foreignObject rendering if browser is capable of
 rendering images

---
 src/Feature.js                        | 63 +++++++++++++-----------
 src/renderer/ForeignObjectRenderer.js | 70 ++++++++++++++++-----------
 2 files changed, 76 insertions(+), 57 deletions(-)

diff --git a/src/Feature.js b/src/Feature.js
index 2e158da..a0cda97 100644
--- a/src/Feature.js
+++ b/src/Feature.js
@@ -1,6 +1,8 @@
 /* @flow */
 'use strict';
 
+import {createForeignObjectSVG, loadSerializedSVG} from './renderer/ForeignObjectRenderer';
+
 const testRangeBounds = document => {
     const TEST_HEIGHT = 123;
 
@@ -72,40 +74,45 @@ const testSVG = document => {
     return true;
 };
 
+const isGreenPixel = data => data[0] === 0 && data[1] === 255 && data[2] === 0 && data[3] === 255;
+
 const testForeignObject = document => {
-    const img = new Image();
     const canvas = document.createElement('canvas');
-    canvas.width = 1;
-    canvas.height = 1;
+    const size = 100;
+    canvas.width = size;
+    canvas.height = size;
     const ctx = canvas.getContext('2d');
+    ctx.fillStyle = 'rgb(0, 255, 0)';
+    ctx.fillRect(0, 0, size, size);
+
+    const img = new Image();
+    const greenImageSrc = canvas.toDataURL();
+    img.src = greenImageSrc;
+    const svg = createForeignObjectSVG(size, size, img);
     ctx.fillStyle = 'red';
-    ctx.fillRect(0, 0, 1, 1);
+    ctx.fillRect(0, 0, size, size);
 
-    img.src = `data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg'><foreignObject><img src="${encodeURIComponent(
-        canvas.toDataURL()
-    )}" /></foreignObject></svg>`;
+    return loadSerializedSVG(svg)
+        .then(img => {
+            ctx.drawImage(img, 0, 0);
+            const data = ctx.getImageData(0, 0, size, size).data;
+            ctx.fillStyle = 'red';
+            ctx.fillRect(0, 0, size, size);
 
-    return new Promise(resolve => {
-        const onload = () => {
-            try {
-                ctx.drawImage(img, 0, 0);
-                canvas.toDataURL();
-            } catch (e) {
-                return resolve(false);
-            }
-
-            return resolve(true);
-        };
-
-        img.onload = onload;
-        img.onerror = () => resolve(false);
-
-        if (img.complete === true) {
-            setTimeout(() => {
-                onload();
-            }, 50);
-        }
-    });
+            const node = document.createElement('div');
+            node.style.backgroundImage = `url(${greenImageSrc})`;
+            node.style.height = `${size}px`;
+            // Firefox 55 does not render inline <img /> tags
+            return isGreenPixel(data)
+                ? loadSerializedSVG(createForeignObjectSVG(size, size, node))
+                : Promise.reject(false);
+        })
+        .then(img => {
+            ctx.drawImage(img, 0, 0);
+            // Edge does not render background-images
+            return isGreenPixel(ctx.getImageData(0, 0, size, size).data);
+        })
+        .catch(e => false);
 };
 
 const FEATURES = {
diff --git a/src/renderer/ForeignObjectRenderer.js b/src/renderer/ForeignObjectRenderer.js
index 81a10eb..10a7f40 100644
--- a/src/renderer/ForeignObjectRenderer.js
+++ b/src/renderer/ForeignObjectRenderer.js
@@ -19,36 +19,48 @@ export default class ForeignObjectRenderer {
         this.ctx.scale(this.options.scale, this.options.scale);
 
         options.logger.log(`ForeignObject renderer initialized with scale ${this.options.scale}`);
+        const svg = createForeignObjectSVG(
+            options.bounds.width,
+            options.bounds.height,
+            this.element
+        );
 
-        const xmlns = 'http://www.w3.org/2000/svg';
-        const svg = document.createElementNS(xmlns, 'svg');
-        const foreignObject = document.createElementNS(xmlns, 'foreignObject');
-        svg.setAttributeNS(null, 'width', options.bounds.width);
-        svg.setAttributeNS(null, 'height', options.bounds.height);
-
-        foreignObject.setAttributeNS(null, 'width', '100%');
-        foreignObject.setAttributeNS(null, 'height', '100%');
-        foreignObject.setAttributeNS(null, 'externalResourcesRequired', 'true');
-        svg.appendChild(foreignObject);
-
-        foreignObject.appendChild(this.element);
-
-        return new Promise((resolve, reject) => {
-            const img = new Image();
-            img.onload = () => {
-                if (options.backgroundColor) {
-                    this.ctx.fillStyle = options.backgroundColor.toString();
-                    this.ctx.fillRect(0, 0, options.bounds.width, options.bounds.height);
-                }
-                this.ctx.drawImage(img, 0, 0);
-                resolve(this.canvas);
-            };
-
-            img.onerror = reject;
-
-            img.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(
-                new XMLSerializer().serializeToString(svg)
-            )}`;
+        return loadSerializedSVG(svg).then(img => {
+            if (options.backgroundColor) {
+                this.ctx.fillStyle = options.backgroundColor.toString();
+                this.ctx.fillRect(0, 0, options.bounds.width, options.bounds.height);
+            }
+            this.ctx.drawImage(img, 0, 0);
+            return this.canvas;
         });
     }
 }
+
+export const createForeignObjectSVG = (width: number, height: number, node: Node) => {
+    const xmlns = 'http://www.w3.org/2000/svg';
+    const svg = document.createElementNS(xmlns, 'svg');
+    const foreignObject = document.createElementNS(xmlns, 'foreignObject');
+    svg.setAttributeNS(null, 'width', width);
+    svg.setAttributeNS(null, 'height', height);
+
+    foreignObject.setAttributeNS(null, 'width', '100%');
+    foreignObject.setAttributeNS(null, 'height', '100%');
+    foreignObject.setAttributeNS(null, 'externalResourcesRequired', 'true');
+    svg.appendChild(foreignObject);
+
+    foreignObject.appendChild(node);
+
+    return svg;
+};
+
+export const loadSerializedSVG = (svg: Node) => {
+    return new Promise((resolve, reject) => {
+        const img = new Image();
+        img.onload = () => resolve(img);
+        img.onerror = reject;
+
+        img.src = `data:image/svg+xml;charset=utf-8,${encodeURIComponent(
+            new XMLSerializer().serializeToString(svg)
+        )}`;
+    });
+};