Added comments, removed unused variables.

Signed-off-by: npalomba <nicola.palomba@studenti.galileilivorno.gov.it>

js/_variables.js

@@ -2,21 +2,22 @@
 var canvasSize,zoom;
 var dragging = false;
 var lastPos = [0,0];
-var canvasPosition;
 var currentTool = 'pencil';
 var currentToolTemp = 'pencil';
 var brushSize = 1;
 var eraserSize = 1;
 var prevBrushSize = 1;
-var prevEraserSize = 1;
-var menuOpen = false;
 var dialogueOpen = false;
 var documentCreated = false;
 
 // Checkerboard management
+// Checkerboard color 1
 var firstCheckerBoardColor = 'rgba(139, 139, 139, 1)';
+// Checkerboard color 2
 var secondCheckerBoardColor = 'rgba(105, 105, 105, 1)';
+// Square size for the checkerboard
 var checkerBoardSquareSize = 16;
+// Checkerboard canvas
 var checkerBoardCanvas = document.getElementById("checkerboard");
 
 //common elements
@@ -27,13 +28,12 @@ var colors = document.getElementsByClassName("color-button");
 var colorsMenu = document.getElementById("colors-menu");
 var popUpContainer = document.getElementById("pop-up-container");
 
-//html canvas
+// main canvas
 var canvas = document.getElementById("pixel-canvas");
 var context = canvas.getContext("2d");
 
 // Layers
 var layers = [];
+// Currently selected layer
 var currentLayer;
 
-//TODO all layers must be moved and resized at the same time
-