setVertexState( vao, indexBuffer = null ) {

		const gl = this.gl;

		if ( this.currentVAO !== vao || this.currentIndex !== indexBuffer ) {

			gl.bindVertexArray( vao );

			if ( indexBuffer !== null ) {

				gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, indexBuffer );

			}

			this.currentVAO = vao;
			this.currentIndex = indexBuffer;

			return true;

		}

		return false;

	}
Sets the vertex state by binding the given VAO and element buffer.

@param {WebGLVertexArrayObject} vao - The VAO.
@param {WebGLBuffer} indexBuffer - The index buffer.
@return {boolean} Whether a vertex state has been changed or not.