ptgolden · August 29, 2015 14:09
diff --git a/index.html b/index.html
 <!DOCTYPE html>
 <meta charset="utf-8">
 <style>
 html, body { margin: 0; padding: 0; }
 #message { height: 3em; width: 800px; text-align: center; padding: 1em 0; box-sizing: border-box;}
 </style>
 <body>
 <script src="http://d3js.org/d3.v3.min.js"></script>
 <div id="message"></div>
 <script>

 var height = 300
  , width = 800
  , padding = 25
  , sensitiveZone = 100


 var svg = d3.select('body').append('svg')
  .attr('height', height + 100)
  .attr('width', width)

 var y = d3.scale.linear()
  .domain([0, 1])
  .range([height - padding, 0])


 // First, I'll set a number of variables that will be changed/monitored by
 // different event callbacks.

 // The line that will extend from one axis to another
 var line = null;

 // The group of sensitive rectangles that will be "sticky" to receive the line
 var sensitiveRects = null;

 // The current sensitive rectangle that is being hovered over
 var enteredEl = null;

 // The source and destination axes of the line.
 var source = null, end = null;

 // A function that returns an absolute X coordinate, relative to the SVG canvas,
 // that is in the middle of the axis path. Takes the <g> axis element as an
 // argument.
 function xCoordFromAxis(axisGroup) {
  var boundingRect = d3.select(axisGroup)
    .select('.domain')[0][0]
    .getBoundingClientRect()

  return boundingRect.left + (boundingRect.width / 2);
 }

 // The behavior that will be called on the sensitive rectangles that are over
 // the axes. Monitors drag events and handles drawing the line.
 var drag = d3.behavior.drag()
  .on('dragstart', function () {

    // Save the reference to the sensitive rectangle which is the source of the
    // drag event.
    var that = this;
    
    // Reset the message at the top.
    document.querySelector('#message').innerHTML = '';

    // Save the source axis and measure.
    // (y.invert(n) is the opposite of y(n)- it takes a pixel measure and returns
    // the scaled value)
    source = { axis: this, measure: y.invert(d3.mouse(this)[1]) }

    // Add event listeners for all the sensitive rectangles that are *not* the
    // source of this event. Store that element when one has been entered
    // (mouseover), and unset that reference when it has been exited (mouseout)
    sensitiveRects = d3.selectAll('rect')
      .filter(function () { return that !== this })
      .on('mouseover', function () { enteredEl = this })
      .on('mouseout', function () { enteredEl = null });
  })
  .on('drag', function (e) {

    // Get the position of the mouse relative to the SVG element
    var mousePos = d3.mouse(svg[0][0])
      , mouseX = mousePos[0]
      , mouseY = mousePos[1]

    // If we have not drawn the line yet, create a new line element and make its
    // origin x coordinate the middle of its source axis and its origin y
    // coordinate the y position of the mouse.
    if (!line) {
      line = svg.insert('line', ':first-child')
        .attr('x1', xCoordFromAxis(source.axis.parentNode))
        .attr('y1', mouseY)
    }

    // If the mouse is over a sensitive rectangle (as set by the mouseover and
    // mouseout listeners set in dragstart), set the terminating point of the
    // line at the middle of the the destination axis and y coordinate of the
    // mouse. Otherwise, set it at the x and y position of the mouse.
    if (enteredEl) {
      dest = { axis: enteredEl, measure: y.invert(d3.mouse(enteredEl)[1]) }
      line.attr('x2', xCoordFromAxis(dest.axis.parentNode))
      line.attr('stroke', 'red');
    } else {
      line.attr('x2', mouseX);
      line.attr('stroke', 'black');
    }

    line.attr('y2', mouseY)
  })
  .on('dragend', function (e) {

    // If the drag ended while over a sensitive rectangle, report the source
    // and desitination mesaures.
    if (enteredEl) {
      document.querySelector('#message').innerHTML = (
        d3.select(source.axis).datum().label +
        '(' + source.measure.toFixed(2) + ') to ' +
        d3.select(dest.axis).datum().label +
        '(' + dest.measure.toFixed(2) + ').'
      )

      var newline = svg.insert('g', ':first-child');
      var lineCoords = {
        x1: xCoordFromAxis(source.axis.parentNode),
        y1: y(source.measure) + 20,
        x2: xCoordFromAxis(dest.axis.parentNode),
        y2: y(dest.measure) + 20,
      }
      newline.append('line')
        .attr(lineCoords)
        .attr('stroke', 'blue')

      newline.append('line')
        .attr(lineCoords)
        .attr('stroke', 'blue')
        .attr('stroke-width', 10)
        .attr('opacity', 0)

      newline.on('dblclick', function (e) { d3.select(this).remove(); return false; })

    }

    // Remove the listeners on the sensitive zones, remove the line.
    sensitiveRects.on('mouseover', null).on('mouseout', null);
    line.remove();

    // Reset all the variables.
    line = null;
    sensitiveRects = null;
    enteredEl = null;
    source = null;
    dest = null;
  })

 var axis = d3.svg.axis()
  .scale(y)
  .orient('left')
  .ticks(5)

 // Draw 4 different axes
 for (var i = 0; i < 4; i++) {
  var axisG = svg.append('g')
    .datum({ label: 'Axis #' + (i + 1) })
    .call(axis)
    .attr('transform', 'translate(' + (50 + i * 200) + ',20)')
    
  axisG.append('text')
    .text(function (d) { return d.label })
    .attr('y', height)
    .attr('text-anchor', 'middle')

  // Draw a rectangle over the axis, and call the drag behavior on it.
  var target = axisG
    .append('rect')
    .attr('height', function () {
        return d3.select(this.parentNode).select('.domain')[0][0].getBoundingClientRect().height
     })
    .attr('width', sensitiveZone)
    .attr('transform', 'translate(-' + (sensitiveZone / 2 + 4) + ',0)')
    .attr('fill', 'grey')
    .style('opacity', '0')
    .call(drag)
 }


 </script>
 </body>
 </html>
	<!DOCTYPE html>
	<meta charset="utf-8">
	<style>
	html, body { margin: 0; padding: 0; }
	#message { height: 3em; width: 800px; text-align: center; padding: 1em 0; box-sizing: border-box;}
	</style>
	<body>
	<script src="http://d3js.org/d3.v3.min.js"></script>
	<div id="message"></div>
	<script>

	var height = 300
	, width = 800
	, padding = 25
	, sensitiveZone = 100


	var svg = d3.select('body').append('svg')
	.attr('height', height + 100)
	.attr('width', width)

	var y = d3.scale.linear()
	.domain([0, 1])
	.range([height - padding, 0])


	// First, I'll set a number of variables that will be changed/monitored by
	// different event callbacks.

	// The line that will extend from one axis to another
	var line = null;

	// The group of sensitive rectangles that will be "sticky" to receive the line
	var sensitiveRects = null;

	// The current sensitive rectangle that is being hovered over
	var enteredEl = null;

	// The source and destination axes of the line.
	var source = null, end = null;

	// A function that returns an absolute X coordinate, relative to the SVG canvas,
	// that is in the middle of the axis path. Takes the <g> axis element as an
	// argument.
	function xCoordFromAxis(axisGroup) {
	var boundingRect = d3.select(axisGroup)
	.select('.domain')[0][0]
	.getBoundingClientRect()

	return boundingRect.left + (boundingRect.width / 2);
	}

	// The behavior that will be called on the sensitive rectangles that are over
	// the axes. Monitors drag events and handles drawing the line.
	var drag = d3.behavior.drag()
	.on('dragstart', function () {

	// Save the reference to the sensitive rectangle which is the source of the
	// drag event.
	var that = this;

	// Reset the message at the top.
	document.querySelector('#message').innerHTML = '';

	// Save the source axis and measure.
	// (y.invert(n) is the opposite of y(n)- it takes a pixel measure and returns
	// the scaled value)
	source = { axis: this, measure: y.invert(d3.mouse(this)[1]) }

	// Add event listeners for all the sensitive rectangles that are not the
	// source of this event. Store that element when one has been entered
	// (mouseover), and unset that reference when it has been exited (mouseout)
	sensitiveRects = d3.selectAll('rect')
	.filter(function () { return that !== this })
	.on('mouseover', function () { enteredEl = this })
	.on('mouseout', function () { enteredEl = null });
	})
	.on('drag', function (e) {

	// Get the position of the mouse relative to the SVG element
	var mousePos = d3.mouse(svg[0][0])
	, mouseX = mousePos[0]
	, mouseY = mousePos[1]

	// If we have not drawn the line yet, create a new line element and make its
	// origin x coordinate the middle of its source axis and its origin y
	// coordinate the y position of the mouse.
	if (!line) {
	line = svg.insert('line', ':first-child')
	.attr('x1', xCoordFromAxis(source.axis.parentNode))
	.attr('y1', mouseY)
	}

	// If the mouse is over a sensitive rectangle (as set by the mouseover and
	// mouseout listeners set in dragstart), set the terminating point of the
	// line at the middle of the the destination axis and y coordinate of the
	// mouse. Otherwise, set it at the x and y position of the mouse.
	if (enteredEl) {
	dest = { axis: enteredEl, measure: y.invert(d3.mouse(enteredEl)[1]) }
	line.attr('x2', xCoordFromAxis(dest.axis.parentNode))
	line.attr('stroke', 'red');
	} else {
	line.attr('x2', mouseX);
	line.attr('stroke', 'black');
	}

	line.attr('y2', mouseY)
	})
	.on('dragend', function (e) {

	// If the drag ended while over a sensitive rectangle, report the source
	// and desitination mesaures.
	if (enteredEl) {
	document.querySelector('#message').innerHTML = (
	d3.select(source.axis).datum().label +
	'(' + source.measure.toFixed(2) + ') to ' +
	d3.select(dest.axis).datum().label +
	'(' + dest.measure.toFixed(2) + ').'
	)

	var newline = svg.insert('g', ':first-child');
	var lineCoords = {
	x1: xCoordFromAxis(source.axis.parentNode),
	y1: y(source.measure) + 20,
	x2: xCoordFromAxis(dest.axis.parentNode),
	y2: y(dest.measure) + 20,
	}
	newline.append('line')
	.attr(lineCoords)
	.attr('stroke', 'blue')

	newline.append('line')
	.attr(lineCoords)
	.attr('stroke', 'blue')
	.attr('stroke-width', 10)
	.attr('opacity', 0)

	newline.on('dblclick', function (e) { d3.select(this).remove(); return false; })

	}

	// Remove the listeners on the sensitive zones, remove the line.
	sensitiveRects.on('mouseover', null).on('mouseout', null);
	line.remove();

	// Reset all the variables.
	line = null;
	sensitiveRects = null;
	enteredEl = null;
	source = null;
	dest = null;
	})

	var axis = d3.svg.axis()
	.scale(y)
	.orient('left')
	.ticks(5)

	// Draw 4 different axes
	for (var i = 0; i < 4; i++) {
	var axisG = svg.append('g')
	.datum({ label: 'Axis #' + (i + 1) })
	.call(axis)
	.attr('transform', 'translate(' + (50 + i * 200) + ',20)')

	axisG.append('text')
	.text(function (d) { return d.label })
	.attr('y', height)
	.attr('text-anchor', 'middle')

	// Draw a rectangle over the axis, and call the drag behavior on it.
	var target = axisG
	.append('rect')
	.attr('height', function () {
	return d3.select(this.parentNode).select('.domain')[0][0].getBoundingClientRect().height
	})
	.attr('width', sensitiveZone)
	.attr('transform', 'translate(-' + (sensitiveZone / 2 + 4) + ',0)')
	.attr('fill', 'grey')
	.style('opacity', '0')
	.call(drag)
	}


	</script>
	</body>
	</html>