Create an clean angle transition for the customers in your map software

So, I am engaged on a mission that entails a map. One of many necessities was to replace not solely the place, but additionally had been the person factors to.

To do that, I built-in the next plugins into the app:

  • flutter_compass – A Flutter compass. The heading varies from 0-360, 0 being north.
  • flutter_map – A flexible mapping bundle for Flutter, based mostly off leaflet.js, that is easy and simple to be taught, but fully customizable and configurable.

For full documentation on the flutter_compass plugin, see the the example page on

Now, to get the continual adjustments within the person’s heading we have to subscribe to the API supplied by the flutter_compass plugin:

double? userHeading;

FlutterCompass.occasions?.pay attention((CompassEvent occasion) {
  userHeading = occasion.heading;
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If route is null this implies the shopper doesn’t have the compass sensor on their gadget, and this state of affairs should be dealt with in order to not have exceptions within the execution of our app.

To show this route worth, you might have a number of approaches:

  • StreamBuilder
  • Supplier
  • ValueNotifier
  • and many others.

However this isn’t the principle subject, so simply use your most well-liked one 😉

For the widget, the plugin’s instance counsel us to make use of Remodel.rotate as follows:

  angle: (route * (math.pi / 180) * -1),
  little one: Picture.asset('property/compass.jpg'),
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In fact, this works, however the angle adjustments are usually not clean, it simply change from one angle worth to the opposite with out transition.

Which different choice do we’ve got???

Animated model of Remodel.rotate which mechanically transitions the kid’s rotation over a given period each time the given rotation adjustments.

However this widget requires a flip worth to verify towards its earlier worth after which animate the transition of the rotation, left to proper (if the worth will increase) or proper to left (if the worth decreases).

Remodel the angle into turns

Okay cool, that is simple proper? Merely divide the route / 360 to get a worth based mostly on the place the person is pointing.

However now we’ll face the primary BIG difficulty:
The compass will misbehave in two eventualities:

  • If the person’s rotation it is from 1 diploma to 360.
  • If the person’s rotation it is from 360 levels to 1.

That is the tough half

As a result of we might want to do some math to only get the variation of the angle after which get the anticipated conduct.

Lets improve our listener operate like this:

double turns = 0;
double prevValue = 0;

FlutterCompass.occasions?.pay attention((CompassEvent occasion) {
  double? route = occasion.heading;

  route = route < 0 ? (360 + route): route;
  double diff = route - prevValue;
  if(diff.abs() > 180) {
    if(prevValue > route) {
      diff = 360 - (route-prevValue).abs();
    } else {
      diff = 360 - (prevValue-route).abs();
      diff = diff * -1;
  turns += (diff / 360);
  prevValue = route;
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We now have in turns the will worth, simply the change between the final and the brand new angle.

The widget ought to appear to be this:

  turns: turns,
  period: const Length(milliseconds: 250),
  little one: const Icon(Icons.arrow_upward_outlined),
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I hope this helps you and saves you a while 😉

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