function makePatch(xScale, yScale, parent, callback){
	var parent = d3.select(parent);
	var xRange = xScale.range(),
		yRange = yScale.range();

	var container = parent.append('g');

	if(!callback){
		var callback = function(x,y){
			console.log(x,y);
		}
	}

	var drag = d3.behavior.drag()
		.origin(patch)
		.on("drag", function(d){
			callback(xScale.invert(d3.event.x), yScale.invert(d3.event.y));
		})

	var patch = container.append('rect')
		.attr('x', Math.min(xRange[0], xRange[1]) )
		.attr('y', Math.min(yRange[0], yRange[1]) )
		.attr('width', Math.abs(xRange[1] - xRange[0]))
		.attr('height', Math.abs(yRange[1] - yRange[0]))
		.attr('class', 'ui-patch')
		.on('click', function(d){
			callback(xScale.invert(d3.event.x), yScale.invert(d3.event.y))
		})
		.call(drag);
}