acity', 0.5)
        .attr('stroke', '#fff')
        .attr('stroke-width', 0.5)
        .attr('fill', pointColor);

    context.append('g')
        .attr('class', 'x brush')
        .call(brush)
        .selectAll('rect')
        .attr('y', -6)
        .attr('height', height);

    function brushend() {
        var filter;
            // If the user has selected no brush area, share everything.
        if (brush.empty()) {
            filter = function() { return true; }
        } else {
            // Othe