3 files changed, 49 insertions, 0 deletions
diff --git a/public/assets/javascripts/rectangles/models/rect.js b/public/assets/javascripts/rectangles/models/rect.js
index 500ee6d..ec32ab7 100644
--- a/public/assets/javascripts/rectangles/models/rect.js
+++ b/public/assets/javascripts/rectangles/models/rect.js
@@ -110,6 +110,10 @@
 	Rect.prototype.fits = function(v){
 		return this.x.length() >= v.a && this.y.length() >= v.b
 	}
+	Rect.prototype.zero = function(){
+		this.a.zero()
+		this.b.zero()
+	}
 	Rect.prototype.nearEdge = function (x, y, r) {
 		var edges = 0
 		if (x < this.x.a+r) {
diff --git a/public/assets/javascripts/rectangles/models/vec2.js b/public/assets/javascripts/rectangles/models/vec2.js
index 2bf286b..104c6f7 100644
--- a/public/assets/javascripts/rectangles/models/vec2.js
+++ b/public/assets/javascripts/rectangles/models/vec2.js
@@ -55,6 +55,9 @@
 		this.b /= n
 		return this
 	}
+	vec2.prototype.zero = function(){
+		this.a = this.b = 0
+	}
 	vec2.prototype.setPosition = function(n){
 		var len = this.length()
 		this.a = n
diff --git a/public/assets/javascripts/rectangles/util/undo.js b/public/assets/javascripts/rectangles/util/undo.js
new file mode 100644
index 0000000..3700817
--- /dev/null
+++ b/public/assets/javascripts/rectangles/util/undo.js
@@ -0,0 +1,42 @@
+(function(){
+
+  var UndoStack = function(){
+    this.stack = []
+    this.types = {}
+    this.pointer = -1
+  }
+  UndoStack.prototype.push = function(action){
+    this.pointer++
+    this.stack[this.pointer] = action
+    this.purge()
+  }
+  UndoStack.prototype.purge = function(){
+    if (this.stack.length-1 == this.pointer) return
+    this.stack.length = this.pointer+1
+  }
+  UndoStack.prototype.undo = function(){
+    if (this.pointer == -1) return false
+    var action = this.stack[this.pointer]
+    this.types[ action.type ].undo(action)
+    this.pointer--
+    return this.pointer > -1
+  }
+  UndoStack.prototype.redo = function(){
+    if (this.pointer == this.stack.length-1) return false
+    this.pointer++
+    var action = this.stack[this.pointer]
+    this.types[ action.type ].redo(action)
+    return this.pointer < this.stack.length-1
+  }
+  UndoStack.prototype.register = function(actionType){
+    this.types[ actionType.type ] = actionType
+  }
+  
+  if ('window' in this) {
+    window.UndoStack = new UndoStack
+  }
+  else {
+    module.exports = new UndoStack
+  }
+
+})()