d3.svg.shadow = function (){
    return d3_svg_shadow('black',9,2);
}

function d3_svg_shadow(color, deviation, multiplication) {
    var id = 0

    function shadow(svg) {
        var filterId = 'shadow-' + id++
        var rgb = d3.rgb(color)
        var filter = svg
            .append('defs')
            .append('filter')
            .attr('id', filterId)
            .attr('x', '-50%')
            .attr('y', '-50%')
            .attr('width', '200%')
            .attr('height', '200%')
        filter.append('feGaussianBlur')
            .attr('in', "SourceAlpha")
            .attr('stdDeviation', deviation)
        for (var i=0; i < multiplication; i++){
            filter.append('feBlend').attr('mode', 'multiply')
        }

        var feComponentTransfer = filter.append('feComponentTransfer')
        feComponentTransfer.append('feFuncR')
            .attr('type', 'linear')
            .attr('slope', 0)
            .attr('intercept', rgb.r / 255)
        feComponentTransfer.append('feFuncG')
            .attr('type', 'linear')
            .attr('slope', 0)
            .attr('intercept', rgb.g / 255)
        feComponentTransfer.append('feFuncB')
            .attr('type', 'linear')
            .attr('slope', 0)
            .attr('intercept', rgb.b / 255)

        var feMerge = filter.append('feMerge')
        feMerge.append('feMergeNode')
        feMerge.append('feMergeNode').attr('in','SourceGraphic')
        return filterId
    }

    shadow.color = function (c){
        if (!arguments.length) return color
        color = c
        return shadow
    }

    shadow.deviation = function (d){
        if (!arguments.length) return deviation
        deviation = d
        return shadow
    }

    shadow.multiplication = function (m){
        if (!arguments.length) return multiplication
        multiplication = m
        return shadow
    }
    return shadow
}