Listening to signature pad changes in AngularJs

I'm using a signature_pad and an email text field which both must be filled before continuing in my web application (x-ng-disabled="!checkSignatureAndEmail()").

The text field has a ng-model so any changes are noticed immediately but the signature pad is plain JavaScript. So if I first enter the email and then sign in the signature pad the button won't become enabled.

Is there any way to register a listener or something like that? If yes, how'd I do this?

<div class="container">
    <div class="modal fade" id="signatureDialog" role="dialog">
        <div class="modal-dialog modal-lg">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal">&times;</button>
                    <h4 class="modal-title">Bestellung best&auml;tigen</h4>
                </div>
                <div class="modal-body">
                    <p>Mit ihrer Unterschrift best&auml;tigen Sie... bla bla..</p>
                    <input type="text" class="form-control" x-ng-model="email">
                    <br>
                    <canvas id="signature-pad" width="700" height="150" style="border:1px solid #B0B0B0; border-radius: 4px;" x-ng-init="initSignaturePad()"></canvas>
                    <br>
                    <button type="button" class="btn btn-default" x-ng-click="signaturePad.clear()">Clear</button>
                </div>
                <div class="modal-footer">
                    <button type="button" class="btn btn-primary" x-ng-disabled="!checkSignatureAndEmail()" x-ng-click="saveOrder(orderInput)" data-dismiss="modal">Best&auml;tigen</button>
                    <button type="button" class="btn btn-default" data-dismiss="modal">Abbrechen</button>
                </div>
            </div>
        </div>
    </div>
</div>

In my controller:

Create SignaturePad:

$scope.initSignaturePad = function() {
    $scope.signaturePad = new SignaturePad(document.getElementById('signature-pad'), {
          minWidth: 1.2,
          maxWidth: 3,
          backgroundColor: 'rgba(250, 250, 250, 1)',
          penColor: 'rgb(0, 0, 100)'
    });
}

Validation function:

$scope.checkSignatureAndEmail = function() {
    var re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    return re.test($scope.email) && !$scope.signaturePad.isEmpty();
};

Solution

Could you try this?

In your HTML, change x-ng-init for x-ng-mouseup event at canvas:

<canvas id="signature-pad" x-ng-mouseup="initSignaturePad()"></canvas>

And in your controller:

  $scope.emptyCanvas = true;

  $scope.$watch('emptyCanvas', function() {
      $scope.checkSignatureAndEmail();
  });

  $scope.checkSignatureAndEmail = function() {
      var re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
      return re.test($scope.email) && !$scope.emptyCanvas;
  };

  $scope.initSignaturePad = function() {    
        $scope.emptyCanvas = $scope.signaturePad.isEmpty();
    };

This works for me, but I don't know if x-ng-mouseup fits your needs.