Issue 24 : Layers

!! NOT STABLE !!
Initial implementation. No UI update yet.
Check js/model/Piskel.js and js/model/Layer.js for an overview of the new
API.

Piskels can be saved on the existing service.

Previous piskels cannot be loaded. This should be fixed soon.

js/model/Layer.js

@@ -0,0 +1,82 @@
+(function () {
+  var ns = $.namespace('pskl.model');
+
+  ns.Layer = function (name) {
+    if (!name) {
+      throw 'Invalid arguments in Layer constructor : \'name\' is mandatory';
+    } else {
+      this.name = name;
+      this.frames = [];
+    }
+  };
+
+  ns.Layer.prototype.getName = function () {
+    return this.name;
+  };
+
+  ns.Layer.prototype.getFrames = function () {
+    return this.frames;
+  };
+
+  ns.Layer.prototype.getFrameAt = function (index) {
+    return this.frames[index];
+  };
+
+  ns.Layer.prototype.addFrame = function (frame) {
+    this.frames.push(frame);
+  };
+
+  ns.Layer.prototype.addFrameAt = function (frame, index) {
+    this.frames.splice(index, 0, frame);
+  };
+
+  ns.Layer.prototype.removeFrame = function (frame) {
+    var index = this.frames.indexOf(frame);
+    this.removeFrameAt(index);
+  };
+
+  ns.Layer.prototype.removeFrameAt = function (index) {
+    if (this.frames[index]) {
+      this.frames.splice(index, 1);
+    } else {
+      throw 'Invalid index in removeFrameAt : ' + index + ' (size : ' + this.length() + ')';
+    }
+  };
+
+  ns.Layer.prototype.moveFrame = function (fromIndex, toIndex) {
+    var frame = this.frames.splice(fromIndex, 1)[0];
+    this.frames.splice(toIndex, 0, frame);
+  };
+
+  ns.Layer.prototype.swapFramesAt = function (fromIndex, toIndex) {
+    var fromFrame = this.frames[fromIndex];
+    var toFrame = this.frames[toIndex];
+    if (fromFrame && toFrame) {
+      this.frames[toIndex] = fromFrame;
+      this.frames[fromIndex] = toFrame;
+    } else {
+      console.log('frames', this.frames);
+      console.log('fromIndex', fromIndex, 'toIndex', toIndex);
+      throw 'Frame not found in moveFrameAt';
+    }
+  };
+
+  ns.Layer.prototype.duplicateFrame = function (frame) {
+    var index = this.frames.indexOf(frame);
+    this.duplicateFrameAt();
+  };
+
+  ns.Layer.prototype.duplicateFrameAt = function (index) {
+    var frame = this.frames[index];
+    if (frame) {
+      var clone = frame.clone();
+      this.addFrameAt(clone, index);
+    } else {
+      throw 'Frame not found in duplicateFrameAt';
+    }
+  };
+
+  ns.Layer.prototype.length = function () {
+    return this.frames.length;
+  };
+})();