Add global mask parsing

examples/parse.js

@@ -2,7 +2,8 @@ var PSD = require('../');
 
 psd = PSD.open('./examples/images/example.psd', function (psd) {
   console.log(psd.header.export());
-  console.log(psd.tree().children()[0].children()[0].nextSibling().export());
+  console.log(psd.tree().export());
+  console.log(psd.layerMask.globalMask);
 });
 // psd.image.saveAsPng('./output.png').then(function () {
 //   console.log("Finished!");

lib/psd/layer_mask.coffee

@@ -36,3 +36,23 @@ module.exports = class LayerMask
         @layers.push new Layer(@file, @header).parse()
 
   parseGlobalMask: ->
+    length = @file.readInt()
+    return if length <= 0
+
+    maskEnd = @file.tell() + length
+
+    @globalMask = _({}).tap (mask) ->
+      mask.overlayColorSpace = @file.readShort()
+      mask.colorComponents = [
+        @file.readShort() >> 8
+        @file.readShort() >> 8
+        @file.readShort() >> 8
+        @file.readShort() >> 8
+      ]
+
+      mask.opacity = @file.readShort() / 16.0
+
+      # 0 = color selected, 1 = color protected, 128 = use value per layer
+      mask.kind = @file.readByte()
+
+    @file.seek maskEnd
\ No newline at end of file