Implement textShadow rendering (Fix #499 and #908)

src/parsing/textShadow.js

@@ -0,0 +1,42 @@
+/* @flow */
+'use strict';
+
+import Color from '../Color';
+
+export type TextShadow = {
+    color: Color,
+    offsetX: number,
+    offsetY: number,
+    blur: number
+};
+
+const TEXT_SHADOW_PROPERTY = /((rgba|rgb)\([^\)]+\)(\s-?\d+px){3})/g;
+const TEXT_SHADOW_VALUES = /(-?\d+px)|(#.+)|(rgb\(.+\))|(rgba\(.+\))/g;
+
+export const parseTextShadow = (textShadow: string): Array<TextShadow> | null => {
+    if (textShadow === 'none') {
+        return null;
+    }
+
+    const shadows = textShadow.match(TEXT_SHADOW_PROPERTY);
+
+    if (!shadows) {
+        return null;
+    }
+
+    const shadowList = [];
+
+    for (let i = 0; i < shadows.length; i++) {
+        const shadow = shadows[i].match(TEXT_SHADOW_VALUES);
+        if (shadow) {
+            shadowList.push({
+                color: new Color(shadow[0]),
+                offsetX: shadow[1] ? parseFloat(shadow[1].replace('px', '')) : 0,
+                offsetY: shadow[2] ? parseFloat(shadow[2].replace('px', '')) : 0,
+                blur: shadow[3] ? parseFloat(shadow[3].replace('px', '')) : 0
+            });
+        }
+    }
+
+    return shadowList;
+};