d3-zoom

What is d3-zoom?

The d3-zoom package is a JavaScript library that allows for interactive zooming and panning of elements in a document, typically used with SVG graphics. It is part of the D3 (Data-Driven Documents) collection of tools for manipulating documents based on data. d3-zoom enables users to apply zoom and pan transformations to visualizations, enhancing the interactivity and accessibility of data representations.

What are d3-zoom's main functionalities?

Zoom and Pan

This feature allows users to add zoom and pan interactions to an SVG element. The 'zoom' event listener applies the transformation to the SVG, updating its position and scale according to user interactions like mousewheel scrolling and dragging.

{"svg.call(d3.zoom().on('zoom', (event) => { svg.attr('transform', event.transform); }))"}

Control Zoom Scale

This feature lets users define the scale extent for the zoom, limiting how much the user can zoom in or out. In this example, the zoom scale is limited between 1x and 8x.

{"svg.call(d3.zoom().scaleExtent([1, 8]).on('zoom', (event) => { svg.attr('transform', event.transform); }))"}

Translate Extent

This feature restricts the panning to a specified rectangular area. In the code sample, the translate extent is set to the dimensions of the SVG, preventing panning outside of the SVG's viewbox.

{"svg.call(d3.zoom().translateExtent([[0, 0], [width, height]]).on('zoom', (event) => { svg.attr('transform', event.transform); }))"}

Programmatic Zooming

This feature allows for programmatic control of the zoom level, enabling transitions to a specific zoom level or transform. In this example, the SVG is programmatically zoomed to 2x scale over a 750ms transition.

{"svg.transition().duration(750).call(zoom.transform, d3.zoomIdentity.scale(2))"}

Other packages similar to d3-zoom

panzoom

Panzoom is a library for panning and zooming elements using CSS transforms. It is similar to d3-zoom but works with both SVG and HTML elements. Unlike d3-zoom, which is tightly integrated with D3's data-driven approach, panzoom is a more general-purpose library that can be used independently of any data visualization library.

leaflet

Leaflet is a JavaScript library for interactive maps. It includes functionalities for zooming and panning over map tiles. While d3-zoom is more generic and can be applied to any SVG element, Leaflet is specifically designed for map interactions and provides a wide range of map-specific features such as markers, layers, and controls.

README

d3-zoom

Panning and zooming are popular interaction techniques which let the user focus on a region of interest by restricting the view. It is easy to learn due to direct manipulation: click-and-drag to pan (translate), spin the wheel to zoom (scale), or use touch. Panning and zooming are widely used in web-based mapping, but can also be used with visualizations such as time-series and scatterplots.

The zoom behavior implemented by d3-zoom is a convenient but flexible abstraction for enabling pan-and-zoom on selections. It handles a surprising variety of input events and browser quirks. The zoom behavior is agnostic about the DOM, so you can use it with SVG, HTML or Canvas.

The zoom behavior is also designed to work with d3-scale and d3-axis; see transform.rescaleX and transform.rescaleY. You can also restrict zooming using zoom.scaleExtent and panning using zoom.translateExtent.

The zoom behavior can be controlled programmatically using zoom.transform, allowing you to implement user interface controls which drive the display or to stage animated tours through your data. Smooth zoom transitions are based on “Smooth and efficient zooming and panning” by Jarke J. van Wijk and Wim A.A. Nuij.

Installing

If you use NPM, npm install d3-zoom. Otherwise, download the latest release. You can also load directly from d3js.org, either as a standalone library or as part of D3 4.0. AMD, CommonJS, and vanilla environments are supported. In vanilla, a d3 global is exported:

<script src="https://d3js.org/d3-color.v0.5.min.js"></script>
<script src="https://d3js.org/d3-dispatch.v0.5.min.js"></script>
<script src="https://d3js.org/d3-ease.v0.8.min.js"></script>
<script src="https://d3js.org/d3-interpolate.v0.9.min.js"></script>
<script src="https://d3js.org/d3-selection.v0.8.min.js"></script>
<script src="https://d3js.org/d3-timer.v0.5.min.js"></script>
<script src="https://d3js.org/d3-transition.v0.3.min.js"></script>
<script src="https://d3js.org/d3-drag.v0.3.min.js"></script>
<script src="https://d3js.org/d3-zoom.v0.3.min.js"></script>
<script>

var zoom = d3.zoom();

</script>

Try d3-zoom in your browser.

API Reference

This table describes how the zoom behavior interprets native events:

Event	Listening Element	Zoom Event	Default Prevented?
mousedown⁵	selection	start	no¹
mousemove²	window¹	zoom	yes
mouseup²	window¹	end	yes
dragstart²	window	-	yes
selectstart²	window	-	yes
click³	window	-	yes
dblclick	selection	multiple⁶	yes
wheel	selection	zoom⁷	yes
touchstart	selection	multiple⁶	no⁴
touchmove	selection	zoom	yes
touchend	selection	end	no⁴
touchcancel	selection	end	no⁴

The propagation of all consumed events is immediately stopped.

¹ Necessary to capture events outside an iframe; see d3-drag#9.
² Only applies during an active, mouse-based gesture; see d3-drag#9.
³ Only applies immediately after a non-empty, mouse-based gesture.
⁴ Necessary to allow click emulation on touch input; see d3-drag#9.
⁵ Ignored if within 500ms of a touch gesture ending; assumes click emulation.
⁶ Double-click and double-tap initiate a transition that emits start, zoom and end events.
⁷ The first wheel event emits a start event; an end event is emitted when no wheel events are received for 150ms.

# d3.zoom()

Creates a new zoom behavior. The returned behavior, zoom, is both an object and a function, and is typically applied to selected elements via selection.call.

# zoom(selection)

Applies this zoom behavior to the specified selection, binding the necessary event listeners to allow panning and zooming, and initializing the zoom transform on each selected element to the identity transform if not already defined. This function is typically not invoked directly, and is instead invoked via selection.call. For example, to instantiate a zoom behavior and apply it to a selection:

selection.call(d3.zoom().on("zoom", zoomed));

Internally, the zoom behavior uses selection.on to bind the necessary event listeners for zooming. The listeners use the name .zoom, so you can subsequently unbind the zoom behavior as follows:

selection.on(".zoom", null);

Applying the zoom behavior also sets the -webkit-tap-highlight-color style to transparent, disabling the tap highlight on iOS. If you want a different tap highlight color, remove or re-apply this style after applying the drag behavior.

# zoom.transform(selection, transform)

If selection is a selection, sets the current zoom transform of the selected elements to the specifed transform, instantaneously emitting start, zoom and end events. If selection is a transition, defines a “zoom” tween to the specified transform using d3.interpolateZoom, emitting a start event when the transition starts, zoom events for each tick of the transition, and then an end event when the transition ends (or is interrupted). The transform may be specified either as a zoom transform or as a function that returns a zoom transform. If a function, it is invoked for each selected element, being passed the current datum d and index i, with the this context as the current DOM element.

This function is typically not invoked directly, and is instead invoked via selection.call or transition.call. For example, to reset the zoom transform to the identity transform instantaneously:

selection.call(zoom.transform, d3.zoomIdentity);

To smoothly reset the zoom transform to the identity transform over 750 milliseconds:

selection.transition().duration(750).call(zoom.transform, d3.zoomIdentity);

This method requires that you specify the new zoom transform completely, and does not enforce the defined scale extent and translate extent, if any. To derive a new transform from the existing transform, and to enforce the scale and translate extents, see the convenience methods zoom.translateBy, zoom.scaleBy and zoom.scaleTo.

# zoom.translateBy(selection, x, y)

If selection is a selection, translates the current zoom transform of the selected elements by x and y, such that the new t_x1 = t_x0 + k × x and t_y1 = t_y0 + k × y. If selection is a transition, defines a “zoom” tween translating the current transform. This method is a convenience method for zoom.transform. The x and y translation amounts may be specified either as numbers or as functions that returns numbers. If a function, it is invoked for each selected element, being passed the current datum d and index i, with the this context as the current DOM element.

# zoom.scaleBy(selection, k)

If selection is a selection, scales the current zoom transform of the selected elements by k, such that the new k₁ = k₀ × k. If selection is a transition, defines a “zoom” tween translating the current transform. This method is a convenience method for zoom.transform. The k scale factor may be specified either as numbers or as functions that returns numbers. If a function, it is invoked for each selected element, being passed the current datum d and index i, with the this context as the current DOM element.

# zoom.scaleTo(selection, k)

If selection is a selection, scales the current zoom transform of the selected elements to k, such that the new k₁ = k. If selection is a transition, defines a “zoom” tween translating the current transform. This method is a convenience method for zoom.transform. The k scale factor may be specified either as numbers or as functions that returns numbers. If a function, it is invoked for each selected element, being passed the current datum d and index i, with the this context as the current DOM element.

# zoom.filter([filter])

If filter is specified, sets the filter to the specified function and returns the zoom behavior. If filter is not specified, returns the current filter, which defaults to:

function filter() {
  return !event.button;
}

If the filter returns falsey, the initiating event is ignored and no zoom gestures are started. Thus, the filter determines which input events are ignored. The default filter ignores mousedown events on secondary buttons, since those buttons are typically intended for other purposes, such as the context menu.

# zoom.extent([extent])

If extent is specified, sets the viewport extent to the specified array of points [[x0, y0], [x1, y1]], where [x0, y0] is the top-left corner of the viewport and [x1, y1] is the bottom-right corner of the viewport, and returns this zoom behavior. The extent may also be specified as a function which returns such an array; if a function, it is invoked for each selected element, being passed the current datum d and index i, with the this context as the current DOM element. If extent is not specified, returns the current extent accessor, which defaults to:

function extent() {
  var svg = this.ownerSVGElement;
  return [[0, 0], svg
      ? [svg.width.baseVal.value, svg.height.baseVal.value]
      : [this.clientWidth, this.clientHeight]];
}

The viewport extent affects several functions: the center of the viewport remains fixed during changes by zoom.scaleBy and zoom.scaleTo; the viewport center and dimensions affect the path chosen by d3.interpolateZoom; and the viewport extent is needed to enforce the optional translate extent

# zoom.scaleExtent([extent])

If extent is specified, sets the scale extent to the specified array of numbers [k0, k1] where k0 is the minimum allowed scale factor and k1 is the maximum allowed scale factor, and returns this zoom behavior. If extent is not specified, returns the current scale extent, which defaults to [0, ∞]. The scale extent restricts zooming in and out. It is enforced on interaction and when using zoom.scaleBy, zoom.scaleTo and zoom.translateBy; however, it is not enforced when using zoom.transform to set the transform explicitly.

# zoom.translateExtent([extent])

If extent is specified, sets the translate extent to the specified array of points [[x0, y0], [x1, y1]], where [x0, y0] is the top-left corner of the world and [x1, y1] is the bottom-right corner of the world, and returns this zoom behavior. If extent is not specified, returns the current translate extent, which defaults to [[-∞, -∞], [+∞, +∞]]. The translate extent restricts panning, and may cause translation on zoom out. It is enforced on interaction and when using zoom.scaleBy, zoom.scaleTo and zoom.translateBy; however, it is not enforced when using zoom.transform to set the transform explicitly.

# zoom.duration([duration])

If duration is specified, sets the duration for zoom transitions on double-click and double-tap to the specified number of milliseconds and returns the zoom behavior. If duration is not specified, returns the current duration, which defaults to 250 milliseconds. If the duration is not greater than zero, double-click and -tap trigger instantaneous changes to the zoom transform rather than initiating smooth transitions.

# zoom.on(typenames[, listener])

If listener is specified, sets the event listener for the specified typenames and returns the zoom behavior. If an event listener was already registered for the same type and name, the existing listener is removed before the new listener is added. If listener is null, removes the current event listeners for the specified typenames, if any. If listener is not specified, returns the first currently-assigned listener matching the specified typenames, if any. When a specified event is dispatched, each listener will be invoked with the same context and arguments as selection.on listeners: the current datum d and index i, with the this context as the current DOM element.

The typenames is a string containing one or more typename separated by whitespace. Each typename is a type, optionally followed by a period (.) and a name, such as zoom.foo and zoom.bar; the name allows multiple listeners to be registered for the same type. The type must be one of the following:

• start - after zooming begins (such as on mousedown).
• zoom - after a change to the zoom transform (such as on mousemove).
• end - after zooming ends (such as on mouseup ).

See dispatch.on for more.

Zoom Events

When a zoom event listener is invoked, d3.event is set to the current zoom event. The event object exposes several fields:

• target - the associated zoom behavior.
• type - the string “start”, “zoom” or “end”; see zoom.on.
• transform - the current zoom transform.
• sourceEvent - the underlying input event, such as mousemove or touchmove.

Zoom Transforms

The zoom behavior stores the zoom state on the element to which the zoom behavior was applied, not on the zoom behavior itself. This is because the zoom behavior can be applied to many elements simultaneously, and each element can be zoomed independently. The zoom state can change either on user interaction or programmatically via zoom.transform.

To retrieve the zoom state, use event.transform on the current zoom event within a zoom event listener (see zoom.on), or use d3.zoomTransform for a given node. The latter is particularly useful for modifying the zoom state programmatically, say to implement buttons for zooming in and out.

# d3.zoomTransform(node)

Returns the current transform for the specified node. Internally, an element’s transform is stored as element.__zoom; however, you should use this method rather than accessing it directly. If the given node has no defined transform, returns the identity transformation. The returned transform represents a two-dimensional transformation matrix of the form:

k 0 t_x
0 k t_y
0 0 1

(This matrix is capable of representing only scale and translation; a future release may also allow rotation, though this would probably not be a backwards-compatible change.) The position ⟨x,y⟩ is transformed to ⟨x × k + t_x,y × k + t_y⟩. The transform object exposes the following properties:

• x - the translation amount t_x along the x-axis.
• y - the translation amount t_y along the y-axis.
• k - the scale factor k.

These properties should be considered read-only; instead of mutating a transform, use transform.scale and transform.translate to derive a new transform. Also see zoom.scaleBy, zoom.scaleTo and zoom.translateBy for convenience methods on the zoom behavior. To create a transform with a given k, t_x, and t_y:

var t = d3.zoomIdentity.translate(x, y).scale(k);

To apply the transformation to a Canvas 2D context, use context.translate followed by context.scale:

context.translate(transform.x, transform.y);
context.scale(transform.k, transform.k);

Similarly, to apply the transformation to HTML elements via CSS:

div.style("transform", "translate(" + transform.x + "px," + transform.y + "px) scale(" + transform.k + ")");

To apply the transformation to SVG:

g.attr("transform", "translate(" + transform.x + "," + transform.y + ") scale(" + transform.k + ")");

Or more simply, taking advantage of transform.toString:

g.attr("transform", transform);

Note that the order of transformations matters! The translate must be applied before the scale.

# transform.scale(k)

Returns a transform whose scale k₁ is equal to k₀ × k, where k₀ is this transform’s scale.

# transform.translate(x, y)

Returns a transform whose translation t_x1 and t_y1 is equal to t_x0 + x and t_y0 + y, where t_x0 and t_y0 is this transform’s translation.

# transform.apply(point)

Returns the transformation of the specified point which is a two-element array of numbers [x, y]. The returned point is equal to [x × k + t_x, y × k + t_y].

# transform.applyX(x)

Returns the transformation of the specified x-coordinate, x × k + t_x.

# transform.applyY(y)

Returns the transformation of the specified y-coordinate, y × k + t_y.

# transform.invert(point)

Returns the inverse transformation of the specified point which is a two-element array of numbers [x, y]. The returned point is equal to [(x - t_x) / k, (y - t_y) / k].

# transform.invertX(x)

Returns the inverse transformation of the specified x-coordinate, (x - t_x) / k.

# transform.invertY(y)

Returns the inverse transformation of the specified y-coordinate, (y - t_y) / k.

# transform.rescaleX(x)

Returns a copy of the continuous scale x whose domain is transformed. This is implemented by first applying the inverse x-transform on the scale’s range, and then applying the inverse scale to compute the corresponding domain:

function rescaleX(x) {
  var range = x.range().map(transform.invertX, transform),
      domain = range.map(x.invert, x);
  return x.copy().domain(domain);
}

The scale x must use d3.interpolateNumber; do not use continuous.rangeRound as this reduces the accuracy of continuous.invert and can lead to an inaccurate rescaled domain. This method does not modify the input scale x; x thus represents the untransformed scale, while the returned scale represents its transformed view.

# transform.rescaleY(y)

Returns a copy of the continuous scale y whose domain is transformed. This is implemented by first applying the inverse y-transform on the scale’s range, and then applying the inverse scale to compute the corresponding domain:

function rescaleY(y) {
  var range = y.range().map(transform.invertY, transform),
      domain = range.map(y.invert, y);
  return y.copy().domain(domain);
}

The scale y must use d3.interpolateNumber; do not use continuous.rangeRound as this reduces the accuracy of continuous.invert and can lead to an inaccurate rescaled domain. This method does not modify the input scale y; y thus represents the untransformed scale, while the returned scale represents its transformed view.

# transform.toString()

Returns a string representing the SVG transform corresponding to this transform. Implemented as:

function toString() {
  return "translate(" + this.x + "," + this.y + ") scale(" + this.k + ")";
}

# d3.zoomIdentity

The identity transform, where k = 1, t_x = t_y = 0.