Fix adding CanvasPattern

The current code was going into an infinite loop
It's also setting `patternUnits` to `userSpaceOnUse` in order to get the same behaviour as canvas patterns

context.js

@@ -371,7 +371,7 @@ export default (function () {
     		})
     	}
 
-        var keys = Object.keys(STYLES), i, style, value, id, regex, matches;
+        var keys = Object.keys(STYLES), i, style, value, regex, matches, id, nodeIndex, node;
         for (i = 0; i < keys.length; i++) {
             style = STYLES[keys[i]];
             value = this[keys[i]];
@@ -381,10 +381,11 @@ export default (function () {
                     //pattern
                     if (value.__ctx) {
                         //copy over defs
-                        while(value.__ctx.__defs.childNodes.length) {
+                        for(nodeIndex = 0; nodeIndex < value.__ctx.__defs.childNodes.length; nodeIndex++){
-                            id = value.__ctx.__defs.childNodes[0].getAttribute("id");
+                          node = value.__ctx.__defs.childNodes[nodeIndex];
+                          id = node.getAttribute("id");
                           this.__ids[id] = id;
-                            this.__defs.appendChild(value.__ctx.__defs.childNodes[0]);
+                          this.__defs.appendChild(node);
                         }
                     }
                     currentElement.setAttribute(style.apply, format("url(#{id})", {id:value.__root.getAttribute("id")}));
@@ -1155,6 +1156,11 @@ export default (function () {
         pattern.setAttribute("id", id);
         pattern.setAttribute("width", image.width);
         pattern.setAttribute("height", image.height);
+        // We want the pattern sizing to be absolute, and not relative
+        // https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Patterns
+        // https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/patternUnits
+        pattern.setAttribute("patternUnits", "userSpaceOnUse");
+
         if (image.nodeName === "CANVAS" || image.nodeName === "IMG") {
             img = this.__document.createElementNS("http://www.w3.org/2000/svg", "image");
             img.setAttribute("width", image.width);

test/index.js

@@ -15,6 +15,7 @@ import setLineDash from './tests/setLineDash'
 import text from './tests/text'
 import tiger from './tests/tiger'
 import transform from './tests/transform'
+import pattern from "./tests/pattern";
 
 const tests = [
     tiger,
@@ -32,7 +33,8 @@ const tests = [
     saveandrestore,
     setLineDash,
     text,
-    transform
+    transform,
+    pattern
 ];
 
 for (let fn of tests) {

test/tests/pattern.js

@@ -0,0 +1,28 @@
+export default function pattern(ctx) {
+  // Create a pattern
+  const patternCanvas = document.createElement('canvas');
+  const patternContext = patternCanvas.getContext('2d');
+
+  // Give the pattern a width and height of 50
+  patternCanvas.width = 50;
+  patternCanvas.height = 50;
+
+  // Give the pattern a background color and draw an arc
+  patternContext.fillStyle = '#fec';
+  patternContext.fillRect(0, 0, patternCanvas.width, patternCanvas.height);
+  patternContext.arc(0, 0, 50, 0, .5 * Math.PI);
+  patternContext.stroke();
+
+  const pattern = ctx.createPattern(patternCanvas, 'repeat');
+  ctx.fillStyle = pattern;
+  ctx.fillRect(0, 0, 50, 50);
+
+  var img = new Image();
+  img.src = 'pattern.png';
+  img.onload = function() {
+    var pattern = ctx.createPattern(img, 'repeat');
+    ctx.fillStyle = pattern;
+    ctx.fillRect(50, 50, 300, 300);
+  };
+
+};