support stroke in pattern.

support stroke="url(#pattern)"

lib/extract/patterns.js

@@ -0,0 +1,53 @@
+import rgba from '../rgba';
+let patterns = {};
+let patternReg = /^url\(#(\w+?)\)$/;
+
+import {LinearGradientGenerator} from '../../elements/LinearGradient';
+import {RadialGradientGenerator} from '../../elements/RadialGradient';
+
+
+function isGradient(obj) {
+    return obj instanceof LinearGradientGenerator || obj instanceof RadialGradientGenerator;
+}
+
+function set(id, pattern) {
+    patterns[id] = pattern;
+}
+
+function remove(id) {
+    delete patterns[id];
+}
+
+export {
+    set,
+    remove
+}
+
+export default function(patternSting, opacity, dimensions, svgId) {
+    if (isGradient(patternSting)) {
+        return patternSting;
+    }
+
+    if (isNaN(opacity)) {
+        opacity = 1;
+    }
+
+    // 尝试匹配 "url(#pattern)"
+    let matched = patternSting.match(patternReg);
+
+    if (matched) {
+        let patternName = `${matched[1]}:${svgId}`;
+        let pattern = patterns[patternName];
+
+        if (pattern) {
+            if (pattern.length === 2) {
+                return pattern(dimensions, opacity);
+            } else {
+                return pattern(opacity);
+            }
+        }
+        return null;
+    }
+
+    return rgba(patternSting, opacity).rgbaString();
+}