setupVariants( builder ) {

		const uv = matcapUV;

		let matcapColor;

		if ( builder.material.matcap ) {

			matcapColor = materialReference( 'matcap', 'texture' ).context( { getUV: () => uv } );

		} else {

			matcapColor = vec3( mix( 0.2, 0.8, uv.y ) ); // default if matcap is missing

		}

		diffuseColor.rgb.mulAssign( matcapColor.rgb );

	}
Setups the matcap specific node variables.

@param {NodeBuilder} builder - The current node builder.