copy( source ) {

		super.copy( source );

		this.source = new Source( Object.assign( {}, source.image ) ); // see #30540
		this.compareFunction = source.compareFunction;

		return this;

	}
Code corresponding to the depth compare function.

@type {?(NeverCompare|LessCompare|EqualCompare|LessEqualCompare|GreaterCompare|NotEqualCompare|GreaterEqualCompare|AlwaysCompare)}
@default null