makeRotation( theta ) {

		// counterclockwise

		const c = Math.cos( theta );
		const s = Math.sin( theta );

		this.set(

			c, - s, 0,
			s, c, 0,
			0, 0, 1

		);

		return this;

	}
Sets this matrix as a 2D rotational transformation.

@param {number} theta - The rotation in radians.
@return {Matrix3} A reference to this matrix.