ng2-panzoom

An Angular directive for panning and zooming an element or elements using the mouse and mousewheel. Code is in place to support touchscreens, but it is completely untested. It was adapted from the angular-pan-zoom library for AngularJS, but it has been heavily modified. Many thanks go out to Martin Vindahl Olsen for writing it.

It is built using Angular CLI 6 library support, so it may not work with Angular versions 2 through 5 (please excuse the 'ng2' moniker).

Demo

Click here for a demo of the module. The demo source can be found here.

Features

• Zoom using mouse wheel, double click, or API controls tied to your own UI.
• Pan using click and drag. When releasing the mouse button whilst panning, the pan will come to a gradual stop.

Differences From the Original

• The pan-zoom service has been eliminated.
• Free zoom - zooming is no longer limited to switching between two distinct zoom levels. Zoom can now be smoothly and freely controlled using the mouse wheel or trackpad.
• zoomToFit() animation - using the zoomToFit() function now will animate the view to the a desired rectangle.
• A convenience method resetView() has been provided to animate the view back to its initial settings.
• The zoomIn() and zoomOut() API functions now zoom to the last zoomed point rather than the centre point, unless no zoom point has been defined yet.
• The widget has not been migrated from the original project, though this probably shouldn't be hard to do. Pull requests are welcome!
• Performance improvements.

Dependencies

• Angular
• jQuery - Used for calculating positions of DOM elements (way easier than using Angular or JS methods).
• ng2-mousewheel - for mouse wheel support.

Installation

npm install ng2-panzoom --save

angular.json:

"projects": {
    "my-angular-app": {
      "architect": {
        "build": {
          "options": {
            "scripts": [
              "node_modules/jquery/dist/jquery.min.js",
              "node_modules/@kensingtontech/hamsterjs/hamster.js"
            ]
            ...

app.module.ts:

import { Ng2PanZoomModule } from 'ng2-panzoom';

@NgModule({
  imports: [  ...,
              Ng2PanZoomModule
           ],
  ...
})

export class MyAppModule { }

Usage

This library exposes a component called 'pan-zoom', under which you may place any standard Angular template code. Though the events which trigger panning and zooming are run outside of Angular and thus themselves will not trigger change detection, it should not break change detection for any sub-components.

A configuration object is required, which gets passed in using [config]="myConfig".

It also exposes an API which can be used to interact with the pan/zoom view. The API is obtained through the configuration object (more below).

Top Tip

Be sure to place your pan-zoom component underneath an element with a definite height/width, like an absolute-positioned div. You may not see anything if you don't do this.

import { PanZoomConfig, PanZoomAPI, PanZoomModel } from 'ng2-panzoom';

@Component({
  selector: 'my-component'
  template: `
    <div style="position: absolute; top: 100px; bottom: 0; left: 0; right: 0;">
      <pan-zoom [config]="panzoomConfig">
        <div style="position: relative;">
          <img src="/myimage1.jpg">
        </div>
      </pan-zoom>
    </div>
  `
})


export class MyComponent {
  ...
  private panZoomConfig: PanZoomConfig = new PanZoomConfig;
  ...
}

Configuration

You must first create and then pass in a configuration object (of type PanZoomConfig) via the config input property. This configuration object also contains RXJS Observables which can be used to work with the API and also observe changes to the panzoom view.

private panZoomConfig: PanZoomConfig = new PanZoomConfig;

The following attributes are defined:

Name	Type	Default	Description
api	BehaviorSubject<PanZoomAPI>	Not Applicable	Subscribe to this observable to obtain access to the API for controlling panzoom programattically. See section below on getting at the API.
zoomLevels	number	5	Number of discrete zoom levels, each one representing a scale. The higher the number, the more zoomed in it is.
neutralZoomLevel	number	2	The zoom level at which the contents render at 1:1 scale.
scalePerZoomLevel	number	2.0	The difference in actual scale between two adjacent zoom levels.
initialZoomLevel	number	neutralZoomLevel	The initially selected zoom level.
initialPanX	number	0	The initial pan in the horizontal direction.
initialPanY	number	0	The initial pan in the vertical direction.
initialZoomToFit	rectangle	undefined	When defined, will initially zoom to fit the given rectangle (see API for explanation of zoom to fit). This overrides the initialZoomLevel, initialPanX, and initialPanY values.
zoomToFitZoomLevelFactor	number	0.95	A number to indicate how closely zoom to fit will work. 1.0 is a perfect fit. Lowering the number will reveal a bit of the surrounding contents.
zoomOnDoubleClick	boolean	true	Enable or disable zooming in on double click.
zoomButtonIncrement	number	1.0	The number of zoom levels to zoom on double click.
zoomStepDuration	number	0.2	Number of seconds to animate between two adjacent zoom levels.
disableZoomAnimation	boolean	false	Set to true to disable the animation while zooming. It will be more chunky but will consume less CPU resources.
zoomOnMouseWheel	boolean	true	Enable or disable zoom in/out on mouse wheel.
invertMouseWheel	boolean	false	Invert the behaviour of the mouse wheel (or two finger trackpad gesture).
freeMouseWheel	boolean	false	By default, moving the mouse wheel will result in a change of zoomButtonIncrement. By setting this to true, the mouse wheel will freely zoom the view without respect to discreet zoom levels.
freeMouseWheelFactor	number	0.08	How much to zoom the view with every tick of the wheel, if using freeMouseWheel.
friction	number	10.0	Constant which controls the friction when dragging and then letting go. The higher the number, the more quickly the animation will come to a stop.
haltSpeed	number	100.0	Constant which controls when the pan animation has slowed down enough to be terminated. The lower the number, the longer it will take to come to a stop.
panOnClickDrag	boolean	true	Enable or disable pan on clicking and dragging the mouse.
modelChanged	Subject<PanZoomModel>	Not Applicable	An RXJS observable which can be subscribed to in order to observe changes to the panzoom view. The model will be passed to the callback function.
useHardwareAcceleration	boolean	true	Use translate3d for panning instead of using standard CSS styles 'left' and 'top'. This is intended to trigger hardware acceleration and may increase the speed greatly.
chromeUseTransform	boolean	true	Cause Chrome to use CSS transform instead of CSS zoom. Enable if you use nested SVG and see performance problems in Chrome.
keepInBounds	boolean	false	When true, it will not be possible to pan the contents off the screen -- it will snap back when trying to do so. It will not be possible to zoom further out than the neutral zoom level. REMEMBER that the initial zoom level must either be less than or equal to the neutral zoom level, or weird things will happen.
keepInBoundsRestoreForce	number	0.5	Constant to control how quickly the contents snap back into place after attempting to pan out of bounds.
keepInBoundsDragPullback	number	0.7	Constant to control the perceived force preventing dragging the contents out of bounds.

API

The panzoom library provides an API for interacting with, observing, and controlling it. The following methods and objects are available from the PanZoomAPI:

• model: PanZoomModel - The current panzoom model - see the PanZoomModel Interface below.

• config: PanZoomConfig - The current panzooom configuration.

• changeZoomLevel(newZoomLevel: number, clickPoint: Point) - This method will reset the view to newZoomLevel, with clickPoint as its centre point.

• zoomIn() - This will zoom the view in to the last zoomed point by one zoom level.

• zoomOut() - This will zoom the view out from the last zoomed point by one zoom level.

• zoomToFit(rectangle: Rect, [duration: number]) - Animates the view to focus on a rectangle of the underlying canvas. duration is how long the animation should take (in seconds), and is optional. rectangle is two coordinates on the canvas which the panZoom view is pan/zooming. See the below section on PanZoom Interfaces for its definition.

• resetView() - A shortcut method to reset the pan and zoom back to the initial view.

• getViewPosition(modelPosition: Point) - By passing in x,y coordinates of the original, untransformed content canvas, it will return the current pixel position of this point.

• getModelPosition(viewPosition: Point) - The reverse operation of getViewPosition().

PanZoom API Interfaces:

interface PanZoomModel {
  zoomLevel: number;
  isPanning?: boolean;
  pan: Point; // the current centre point of the pan/zoom view
}

interface Point {
  x: number;
  y: number;
}

interface Rect {
  x: number; // the x0 (top left) coordinate
  y: number; // the y0 (top left) coordinate
  width: number; // the x1 (bottom right) coordinate
  height: number; // the y1 (bottom right) coordinate
}

Getting at the API

The panzoom API is exposed through an RXJS observable as a property of the PanZoomConfig class, named api, to which you simply subscribe to obtain the API object. The subscription callback method will be passed the API as its only parameter, of type PanZoomAPI. Because it uses a BehaviorSubject, the callback will immediately trigger when subscribed to, assuming panzoom has already been initialised. If panzoom hasn't yet been initialised, the subscription callback will fire as soon as initialisation occurs.

import { PanZoomConfig, PanZoomAPI, PanZoomModel } from 'ng2-panzoom';
import { Subscription } from 'rxjs';

@Component({ ... })

export class MyComponent implements OnInit, OnDestroy {
 
  private panZoomConfig: PanZoomConfig = new PanZoomConfig;
  private panZoomAPI: PanZoomAPI;
  private apiSubscription: Subscription;

  ngOnInit(): void {
    this.apiSubscription = this.panzoomConfig.api.subscribe( (api: PanZoomAPI) => this.panZoomAPI = api );
  }

  ngOnDestroy(): void {
    this.apiSubscription.unsubscribe();  // don't forget to unsubscribe.  you don't want a memory leak!
  }

}

Now that we have our API stored in this.panZoomAPI, we can access it thusly:

this.panZoomAPI.zoomIn();
this.panZoomAPI.zoomOut();

'Events'

The PanZoomConfig class has an RXJS observable (modelChanged) which can be used to monitor the pan/zoom state from another component. The observable emits type PanZoomModel (see above section on API Interfaces). For instance, when the zoom level reaches a certain level, you may want to display a custom control or content on your page. Another use may be to do something when the panzoom centre point is over a certain part of the view.

Example modelChanged Subscription

import { PanZoomConfig, PanZoomAPI, PanZoomModel } from 'ng2-panzoom';

@Component({ ... })

export class MyComponent implements OnInit, OnDestroy {
 
  private panZoomConfig: PanZoomConfig = new PanZoomConfig;
  private modelChangedSubscription: Subscription;

  ngOnInit(): void {
    this.modelChangedSubscription = this.panzoomConfig.modelChanged.subscribe( (model: PanZoomModel) => this.onModelChanged(model) );
  }

  ngOnDestroy(): void {
    this.modelChangedSubscription.unsubscribe();  // don't forget to unsubscribe.  you don't want a memory leak!
  }

  onModelChanged(model: PanZoomModel): void {
    // do something after receiving your model update here
  }

}

Contributing

Pull requests are welcome.

Reference

ng2-mousewheel project

The original angular-pan-zoom project on GitHub