_getWebGLDrawRect() {
        this._computeWebGLBoundingRect();

        return {
            top: this._boundingRect.worldToDocument.top - this.drawCheckMargins.top,
            right: this._boundingRect.worldToDocument.right + this.drawCheckMargins.right,
            bottom: this._boundingRect.worldToDocument.bottom + this.drawCheckMargins.bottom,
            left: this._boundingRect.worldToDocument.left - this.drawCheckMargins.left,
        };
    }
Returns our plane WebGL bounding rectangle in document coordinates including additional drawCheckMargins

     returns :
     @boundingRectangle (obj): an object containing our plane WebGL element bounding rectangle including the draw check margins (top, bottom, right and left properties)
*