code: function(color, ctx){
              ctx = ctx || this.bufferCtx;
              ctx.fillStyle = color || this.bgColor;
              ctx.fillRect(
                  0,
                  0,
                  this.canvas.width,
                  this.canvas.height
              );
          }
docs: Fills the canvas with a given color.
  @method fillBg
  @param {String} [color=this.bgColor]
  @param {CanvasRenderingContext2D} [ctx=this.bufferCtx]