_createMaterial() {

		const material = new NodeMaterial();
		material.isMeshToonOutlineMaterial = true;
		material.name = 'Toon_Outline';
		material.side = BackSide;

		// vertex node

		const outlineNormal = normalLocal.negate();
		const mvp = cameraProjectionMatrix.mul( modelViewMatrix );

		const ratio = float( 1.0 ); // TODO: support outline thickness ratio for each vertex
		const pos = mvp.mul( vec4( positionLocal, 1.0 ) );
		const pos2 = mvp.mul( vec4( positionLocal.add( outlineNormal ), 1.0 ) );
		const norm = normalize( pos.sub( pos2 ) ); // NOTE: subtract pos2 from pos because BackSide objectNormal is negative

		material.vertexNode = pos.add( norm.mul( this.thicknessNode ).mul( pos.w ).mul( ratio ) );

		// color node

		material.colorNode = vec4( this.colorNode, this.alphaNode );

		return material;

	}
Creates the material used for outline rendering.

@private
@return {NodeMaterial} The outline material.