setPolygonOffset( polygonOffset, factor, units ) {

		const { gl } = this;

		if ( polygonOffset ) {

			this.enable( gl.POLYGON_OFFSET_FILL );

			if ( this.currentPolygonOffsetFactor !== factor || this.currentPolygonOffsetUnits !== units ) {

				gl.polygonOffset( factor, units );

				this.currentPolygonOffsetFactor = factor;
				this.currentPolygonOffsetUnits = units;

			}

		} else {

			this.disable( gl.POLYGON_OFFSET_FILL );

		}

	}
Specifies the polygon offset.

This method caches the state so `gl.polygonOffset()` is only
called when necessary.

@param {boolean} polygonOffset - Whether polygon offset is enabled or not.
@param {number} factor - The scale factor for the variable depth offset for each polygon.
@param {number} units - The multiplier by which an implementation-specific value is multiplied with to create a constant depth offset.