d3.js change zoom behavior to semantic zoom

Question

I'm doing some tests with d3.js regarding zooming. At the moment, I have successfully implemented geometric zoom in my test, but it has a drawback: the elements under the zoomed g are being scaled. As I understood it, this could be solved by using semantic zooming.

The problem is that I need scale in my test, as I'm syncing it with a jQuery.UI slider value.

On the other hand, I would like the text elements being resized to maintain their size after a zoom operation.

I have an example of my current attempt here.

I'm having trouble changing my code to fit this purpose. Can any one share some insight/ideas?

Answer 1

For your solution I have merged 2 examples:

• Semantic Zooming
• Programmatic Zooming

Code snippets:

function zoom() {
  text.attr("transform", transform);
  var scale = zoombehavior.scale();
  //to make the scale rounded to 2 decimal digits
  scale = Math.round(scale * 100) / 100;
  //setting the slider to the new value
  $("#slider").slider( "option", "value", scale );
  //setting the slider text to the new value
  $("#scale").val(scale);
}
//note here we are not handling the scale as its Semantic Zoom
function transform(d) {
  //translate string
  return "translate(" + x(d[0]) + "," + y(d[1]) + ")";
}

function interpolateZoom(translate, scale) {
  zoombehavior
        .scale(scale)//we are setting this zoom only for detecting the scale for slider..we are not zoooming using scale.
        .translate(translate);
      zoom();
}
var slider = $(function() {
  $("#slider").slider({
    value: zoombehavior.scaleExtent()[0],//setting the value
    min: zoombehavior.scaleExtent()[0],//setting the min value
    max: zoombehavior.scaleExtent()[1],//settinng the ax value
    step: 0.01,
    slide: function(event, ui) {
      var newValue = ui.value;
      var  center = [centerX, centerY],
        extent = zoombehavior.scaleExtent(),
        translate = zoombehavior.translate(),
        l = [],
        view = {
          x: translate[0],
          y: translate[1],
          k: zoombehavior.scale()
        };
      //translate w.r.t the center
      translate0 = [(center[0] - view.x) / view.k, (center[1] - view.y) / view.k];
      view.k = newValue;//the scale as per the slider
      //the translate after the scale(so we are multiplying the translate)
      l = [translate0[0] * view.k + view.x, translate0[1] * view.k + view.y];

      view.x += center[0] - l[0];
      view.y += center[1] - l[1];

      interpolateZoom([view.x, view.y], view.k);

    }
  });
});

I am zooming w.r.t. 250,250 which is the center of the clip circle.

Working code here (have added necessary comments)

Hope this helps!

Answer 2

To do what you want, you need to refactor the code first a little bit. With d3, it is good practice to use data() to append items to a selection, rather than using for loops.

So this :

for(i=0; i<7; i++){
	pointsGroup.append("text")
  			  .attr("x", function(){
              	var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
                var randx = Math.random();
                return Math.floor(plusOrMinus*randx*75)+centerx;
              })
              .attr("y", function(){
              	var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
                var randy = Math.random();
                return Math.floor(plusOrMinus*randy*75)+centery;
              })
              .html("star")
              .attr("class", "point material-icons")
              .on("click", function(){console.log("click!");});
}

Becomes this

var arr = [];

for(i=0; i<7; i++){
  var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
  var randx = Math.random();
  var x = Math.floor(plusOrMinus*randx*75)+centerx; 
  
  var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
  var randy = Math.random();
  var y = Math.floor(plusOrMinus*randy*75)+centery;
  
  arr.push({"x":x,"y":y});
}
	
pointsGroup.selectAll("text")
            .data(arr)
            .enter()
            .append("text")
            .attr("x", function(d,i){
              	return d.x;// This corresponds to arr[i].x
              })
            .attr("y", function(d,i){
             	return d.y;// This corresponds to arr[i].y
              })
            .html("star")
            .attr("class", "point material-icons")
            .on("click", function(){console.log("click!");});

This way, you can access individual coordinates using for instance.attr("x",function(d,i){ //d.x is equal to arr.x, i is item index in the selection});

Then, to achieve your goal, rather than changing the scale of your items, you should use a linear scale to change each star position.

First, add linear scales to your fiddle and apply them to the zoom:

var scalex = d3.scale.linear();
var scaley = d3.scale.linear();

var zoom = d3.behavior.zoom().x(scalex).y(scaley).scaleExtent([1, 5]).on('zoom', onZoom);

And finally on zoom event apply the scale to each star's x and y

function onZoom(){
  d3.selectAll("text")
    .attr("x",function(d,i){
      
      return scalex(d.x);
    })
    .attr("y",function(d,i){
     
      return scaley(d.y);
    });
}

At this point, zoom will work without the slider. To add the slider, simply change manually the zoom behavior scale value during onSlide event, then call onZoom.

function onSlide(scale){
  var sc = $("#slider").slider("value");
  zoom.scale(sc);
  onZoom();
}

Note: I used this config for the slider:

var slider = $(function() {
	    $( "#slider" ).slider({
			value: 1,
			min: 1,
			max: 5,
			step: 0.1,
			slide: function(event, ui){
              onSlide(5/ui.value);
			}
	    });
	});

Please note that at this point the zoom from the ui is performed relative to (0,0) at this point, and not your "circle" window center. To fix it I simplified the following function from the programmatic example, that computes valid translate and scale to feed to the zoom behavior.

// To handle center zooming
var width = 500;
var height = 600;

function zoomClick(sliderValue) {
  var center = [width / 2, height / 2],
    extent = zoom.scaleExtent(),
    translate = zoom.translate();


  var view = {
    x: zoom.translate()[0],
    y: zoom.translate()[1],
    k: zoom.scale()
  };

  var target_zoom = sliderValue;

  if (target_zoom < extent[0] || target_zoom > extent[1]) {
    return false;
  }

  var translate0 = [(center[0] - view.x) / view.k, (center[1] - view.y) / view.k];

  view.k = target_zoom;
  var l = [];
  l = [translate0[0] * view.k + view.x, translate0[1] * view.k + view.y];

  view.x += center[0] - l[0];
  view.y += center[1] - l[1];

  // [view.x view.y] is valid translate
  // view.k is valid scale
  // Then, simply feed them to the zoom behavior
  zoom
    .scale(view.k)
    .translate([view.x, view.y]);
  // and call onZoom to update points position
  onZoom();

}

then just change onSlide to use this new function every time slider moves

function onSlide(scale){
  var sc = $("#slider").slider("value");
  zoomClick(sc);
}

Full snippet

function onZoom(){
  d3.selectAll("text")
    .attr("x",function(d,i){
      
      return scalex(d.x);
    })
    .attr("y",function(d,i){
     
      return scaley(d.y);
    });
}


function onSlide(scale){
  var sc = $("#slider").slider("value");
  zoomClick(sc);
}

var scalex = d3.scale.linear();
var scaley = d3.scale.linear();

var zoom = d3.behavior.zoom().x(scalex).y(scaley).scaleExtent([1, 5]).on('zoom', onZoom);

var svg = d3.select("body").append("svg")
                            .attr("height", "500px")
                            .attr("width", "500px")
					        .call(zoom)
					        .on("mousedown.zoom", null)
					        .on("touchstart.zoom", null)
    				        .on("touchmove.zoom", null)
    				        .on("touchend.zoom", null);

var centerx = 250,
    centery = 250;

var circleGroup = svg.append("g")
                      .attr("id", "circleGroup");

var circle = circleGroup.append("circle")
                  .attr("cx", "50%")
                  .attr("cy", "50%")
                  .attr("r", 150)
                  .attr("class", "circle");



var pointsParent = svg.append("g").attr("clip-path", "url(#clip)").attr("id", "pointsParent");

var pointsGroup = pointsParent.append("g")
					  .attr("id", "pointsGroup");

var arr = [];

for(i=0; i<7; i++){
  var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
  var randx = Math.random();
  var x = Math.floor(plusOrMinus*randx*75)+centerx; 
  
  var plusOrMinus = Math.random() < 0.5 ? -1 : 1;
  var randy = Math.random();
  var y = Math.floor(plusOrMinus*randy*75)+centery;
  
  arr.push({"x":x,"y":y});
}
	
pointsGroup.selectAll("text")
            .data(arr)
            .enter()
            .append("text")
            .attr("x", function(d,i){
              	return d.x;// This corresponds to arr[i].x
              })
            .attr("y", function(d,i){
             	return d.y;// This corresponds to arr[i].y
              })
            .html("star")
            .attr("class", "point material-icons")
            .on("click", function(){console.log("click!");});

zoom(pointsGroup);

var clip = svg.append("defs").append("svg:clipPath")
        .attr("id", "clip")
        .append("svg:circle")
        .attr("id", "clip-circ")
        .attr("cx", centerx)
        .attr("cy", centery)
        .attr("r", 149);

var slider = $(function() {
	    $( "#slider" ).slider({
			value: 1,
			min: 1,
			max: 5,
			step: 0.1,
			slide: function(event, ui){
              onSlide(5/ui.value);
			}
	    });
	});



// To handle center zooming
var width = 500;
var height = 600;

function zoomClick(sliderValue) {
    var target_zoom = 1,
        center = [width / 2, height / 2],
        extent = zoom.scaleExtent(),
        translate = zoom.translate();
        
    
    var view = {x: zoom.translate()[0], y: zoom.translate()[1], k: zoom.scale()};
  
    target_zoom = sliderValue;

    if (target_zoom < extent[0] || target_zoom > extent[1]) { return false; }

    var translate0 = [];
    translate0 = [(center[0] - view.x) / view.k, (center[1] - view.y) / view.k];
  
    view.k = target_zoom;
    var l = [];
    l = [translate0[0] * view.k + view.x, translate0[1] * view.k + view.y];

    view.x += center[0] - l[0];
    view.y += center[1] - l[1];
  
    zoom
       .scale(view.k)
       .translate([view.x, view.y]);
    onZoom();
  
}

body {
  font: 10px sans-serif;
}

text {
  font: 10px sans-serif;
}

.circle{
  stroke: black;
  stroke-width: 2px;
  fill: white;
}

.point{
  fill: goldenrod;
  cursor: pointer;
}

.blip{
  fill: black;
}

#slider{
  width: 200px;
  margin: auto;
}

<!DOCTYPE html>
<html>
<head>
<link href="https://fonts.googleapis.com/icon?family=Material+Icons"
      rel="stylesheet">
<link href="https://code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css" rel="stylesheet" type="text/css" />
<script src="https://code.jquery.com/jquery-1.11.3.js"></script>
<script src="https://code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js"></script>
  

<meta charset=utf-8 />
<title>d3.JS slider zoom</title>
</head>
  
<body>
  <div id="slider"></div>
</body>
</html>