allow row domain not to start/end at zero

[gordonwoodhull]

This is related to #646, which also needs better control over the zero point of the chart.

It came up in this SO question: dcjs dynamic zooming to fit range of values (thanks Isaac!)

The row chart expects always to start at zero and has code to set either the start or the end of the domain to zero:

dc.js/src/row-chart.js

Lines 53 to 66 in 7c55500

	function calculateAxisScale () {
	if (!_x || _elasticX) {
	var extent = d3.extent(_rowData, _chart.cappedValueAccessor);
	if (extent[0] > 0) {
	extent[0] = 0;
	}
	if (extent[1] < 0) {
	extent[1] = 0;
	}
	_x = d3.scaleLinear().domain(extent)
	.range([0, _chart.effectiveWidth()]);
	}
	_xAxis.scale(_x);
	}

Then it draws the rects starting from where the scale says zero is:

dc.js/src/row-chart.js

Lines 167 to 170 in 7c55500

	function rootValue () {
	var root = _x(0);
	return (root === -Infinity || root !== root) ? _x(1) : root;
	}

If the range start is not zero, this will be off the chart.

Example fiddle

A temporary fix, but it has flicker because, as usual, it's fighting with the chart's transitions and pretransition won't work here. _{Well maybe it could with more work.}

chart.on('renderlet', function(chart) {
    var transform = chart.select('g.row rect').attr('transform');
    var tx = +transform.split('(')[1].split(',')[0];
    chart.selectAll('g.row rect')
        .attr('transform', null)
        .attr('width', function(d) {
            return +d3.select(this).attr('width') + tx;
        })
    chart.selectAll('g.row text.row')
        .attr('transform', null);    
})