drawDebuggingRect(rect) {
        var context = this.context;
        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 rectangle onto the canvas
@param {OpenSeadragon.Rect} rect