Add layer.center offsets and chaining

framer/Layer.coffee

@@ -233,9 +233,17 @@ class exports.Layer extends BaseClass
 			frame.midY = parseInt window.innerHeight / 2.0
 			return frame
 
-	center: -> @frame = @centerFrame() # Center  in superLayer
-	centerX: -> @x = @centerFrame().x # Center x in superLayer
-	centerY: -> @y = @centerFrame().y # Center y in superLayer
+	center: ->
+		@frame = @centerFrame() # Center  in superLayer
+		@
+
+	centerX: (offset=0) ->
+		@x = @centerFrame().x + offset # Center x in superLayer
+		@
+
+	centerY: (offset=0) ->
+		@y = @centerFrame().y + offset # Center y in superLayer
+		@
 
 	pixelAlign: ->
 		@x = parseInt @x

test/tests/LayerTest.coffee

@@ -575,6 +575,40 @@ describe "Layer", ->
 			layer.maxY = 200
 			layer.y.should.equal 100
 
+	describe "Center", ->
+
+		it "should center", ->
+			layerA = new Layer width:200, height:200
+			layerB = new Layer width:100, height:100, superLayer:layerA
+			layerB.center()
+
+			assert.equal layerB.x, 50
+			assert.equal layerB.y, 50
+
+		it "should center with offset", ->
+			layerA = new Layer width:200, height:200
+			layerB = new Layer width:100, height:100, superLayer:layerA
+			layerB.centerX(50)
+			layerB.centerY(50)
+
+			assert.equal layerB.x, 100
+			assert.equal layerB.y, 100
+
+		it "should center return layer", ->
+			layerA = new Layer width:200, height:200
+			layerA.center().should.equal layerA
+			layerA.centerX().should.equal layerA
+			layerA.centerY().should.equal layerA
+
+		it "should center pixel align", ->
+			layerA = new Layer width:200, height:200
+			layerB = new Layer width:111, height:111, superLayer:layerA
+			layerB.center().pixelAlign()
+
+			assert.equal layerB.x, 44
+			assert.equal layerB.y, 44
+
+
 	describe "CSS", ->
 
 		it "classList should work", ->