code: function() {
          this.canvas.innerHTML = "";
          if ( this.useCanvas ) {
              var viewportSize = this._calculateCanvasSize();
              if( this.canvas.width != viewportSize.x ||
                  this.canvas.height != viewportSize.y ) {
                  this.canvas.width = viewportSize.x;
                  this.canvas.height = viewportSize.y;
                  this._updateImageSmoothingEnabled(this.context);
                  if ( this.sketchCanvas !== null ) {
                      var sketchCanvasSize = this._calculateSketchCanvasSize();
                      this.sketchCanvas.width = sketchCanvasSize.x;
                      this.sketchCanvas.height = sketchCanvasSize.y;
                      this._updateImageSmoothingEnabled(this.sketchContext);
                  }
              }
              this._clear();
          }
      }
docs: Clears the Drawer so it's ready to draw another frame.