drawDebuggingRect(rect){
            let context = this._outputContext;
            context.save();
            context.lineWidth = 2 * $.pixelDensityRatio;
            context.strokeStyle = this.debugGridColor[0];
            context.fillStyle = this.debugGridColor[0];

            context.strokeRect(
                rect.x * $.pixelDensityRatio,
                rect.y * $.pixelDensityRatio,
                rect.width * $.pixelDensityRatio,
                rect.height * $.pixelDensityRatio
            );

            context.restore();
        }
Draw a rect onto the output canvas for debugging purposes
@param {OpenSeadragon.Rect} rect