Viewport Transition

@goongmaps/goong-map-react does not expose the transition API from goong-js since it is designed to be a stateless component, and needs to synchronize with separate overlay systems such as deck.gl.

Instead, transitions can be defined using InteractiveMap's transition props.

Example: Fly to a New Location

import * as React from 'react';
import ReactMapGL, {FlyToInterpolator} from '@goongmaps/goong-map-react';
// 3rd-party easing functions
import d3 from 'd3-ease';

function App() {
  const [viewport, setViewport] = React.useState({
    width: 800,
    height: 600,
    latitude: 37.78,
    longitude: -122.45,
    zoom: 14
  });

  const goToNYC = () => {
    setViewport({
      ...viewport,
      longitude: -74.1,
      latitude: 40.7,
      zoom: 14,
      transitionDuration: 5000,
      transitionInterpolator: new FlyToInterpolator(),
      transitionEasing: d3.easeCubic
    });
  };

  return (
    <div>
      <ReactMapGL {...viewport} onViewportChange={setViewport} />
      <button onClick={goToNYC}>New York City</button>
    </div>
  );
}

See viewport animation for a complete example.

Example: Transition Viewport To A Bounding Box

You can use the WebMercatorViewport utility to find the target viewport that fits around a lngLat bounding box:

import {WebMercatorViewport} from '@goongmaps/goong-map-react';

  const goToSF = () => {
    const {longitude, latitude, zoom} = new WebMercatorViewport(viewport)
        .fitBounds([[-122.4, 37.7], [-122.5, 37.8]], {
          padding: 20,
          offset: [0, -100]
        });
    setViewport({
      ...viewport,
      longitude,
      latitude,
      zoom,
      transitionDuration: 5000,
      transitionInterpolator: new FlyToInterpolator(),
      transitionEasing: d3.easeCubic
    });
  };

Documentation of WebMercatorViewport

Controlling Map Transitions

InteractiveMap's Transition Props

See properties of InteractiveMap.

• transitionDuration (Number)
• transitionInterpolator (Object)
• transitionEasing (Function)
• transitionInterruption (Number)
• onTransitionStart (Function)
• onTransitionInterrupt (Function)
• onTransitionEnd (Function)

Transition and the onViewportChange Callback

InteractiveMap is designed to be a stateless component. For transitions to work, the application must update the viewport props returned by the onViewportChange callback:

<ReactMapGL {...viewport} onViewportChange={setViewport} />

Remarks:

• The props returned by the callback may contain transition properties. For example, during panning and rotating, the callback is invoked with transitionDuration: 0, meaning that the map movement instantly matches the change of the pointer. When panning or zooming with keyboard, the callback is invoked with a 300ms linear transition.
• It is recommended that when programatically triggering a transition, always explicitly set the transition properties (interpolator, easing and duration).
• "Set and forget": the values of the following props at the start of a transition carry through the entire duration of the transition:
  • transitionDuration
  • transitionInterpolator
  • transitionEasing
  • transitionInterruption
• The default interaction/transition behavior can always be intercepted and overwritten in the handler for onViewportChange. However, if a transition is in progress, the properties that are being transitioned (e.g. longitude and latitude) should not be manipulated, otherwise the change will be interpreted as an interruption of the transition.
• When using FlyToInterpolator for transitionInterpolator, transitionDuration can be set to 'auto' where actual duration is auto calculated based on start and end viewports and is linear to the distance between them. This duration can be further customized using speed parameter to FlyToInterpolator constructor.

Transition Interpolators

A TransitionInterpolator instance must be supplied to the transitionInterpolator prop. It contains the following methods:

• arePropsEqual(currentProps, nextProps) - called to determine if transition should be triggered when viewport props update.
• initiateProps(startProps, endProps) - called before transition starts to pre-process the start and end viewport props.
• interpolateProps(startProps, endProps, t) - called to get viewport props in transition. t is a time factor between [0, 1].

@goongmaps/goong-map-react offers two built-in interpolator classes:

• LinearInterpolator
• FlyToInterpolator