Feature: isDrawing

lib/src/controllers/notifications/is_drawing_state_changed.dart

@@ -0,0 +1,10 @@
+import 'notification.dart';
+
+/// A notification that is dispatched when the user starts or stops freehand painting
+class DrawableIsDrawingStateChangedNotification
+    extends FlutterPainterNotification {
+  bool isDrawing;
+
+  /// Creates a [DrawableIsDrawingStateChangedNotification]. Supplies the current Drawable and also if the user started or stopped
+  DrawableIsDrawingStateChangedNotification(this.isDrawing);
+}

lib/src/views/widgets/flutter_painter.dart

@@ -5,6 +5,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter_painter/src/controllers/notifications/is_drawing_state_changed.dart';
 import '../../controllers/events/selected_object_drawable_removed_event.dart';
 import '../../controllers/helpers/renderer_check/renderer_check.dart';
 import '../../controllers/drawables/drawable.dart';
@@ -54,6 +55,9 @@ class FlutterPainter extends StatelessWidget {
   /// Callback when the [PainterSettings] of [PainterController] are updated internally.
   final ValueChanged<PainterSettings>? onPainterSettingsChanged;
 
+  /// Callback when a [FreeStyleDrawable] starts or stops being drawn
+  final ValueChanged<bool>? onIsDrawingStateChanged;
+
   /// The builder used to build this widget.
   ///
   /// Using the default constructor, it will default to returning the [_FlutterPainterWidget].
@@ -63,29 +67,31 @@ class FlutterPainter extends StatelessWidget {
   final FlutterPainterBuilderCallback _builder;
 
   /// Creates a [FlutterPainter] with the given [controller] and optional callbacks.
-  const FlutterPainter(
-      {Key? key,
-      required this.controller,
-      this.onDrawableCreated,
-      this.onDrawableDeleted,
-      this.onSelectedObjectDrawableChanged,
-      this.onPainterSettingsChanged})
-      : _builder = _defaultBuilder,
+  const FlutterPainter({
+    Key? key,
+    required this.controller,
+    this.onDrawableCreated,
+    this.onDrawableDeleted,
+    this.onSelectedObjectDrawableChanged,
+    this.onPainterSettingsChanged,
+    this.onIsDrawingStateChanged,
+  })  : _builder = _defaultBuilder,
         super(key: key);
 
   /// Creates a [FlutterPainter] with the given [controller], [builder] and optional callbacks.
   ///
   /// Using this constructor, the [builder] will be called any time the [controller] updates.
   /// It is useful if you want to build UI that automatically rebuilds on updates from [controller].
-  const FlutterPainter.builder(
-      {Key? key,
-      required this.controller,
-      required FlutterPainterBuilderCallback builder,
-      this.onDrawableCreated,
-      this.onDrawableDeleted,
-      this.onSelectedObjectDrawableChanged,
-      this.onPainterSettingsChanged})
-      : _builder = builder,
+  const FlutterPainter.builder({
+    Key? key,
+    required this.controller,
+    required FlutterPainterBuilderCallback builder,
+    this.onDrawableCreated,
+    this.onDrawableDeleted,
+    this.onSelectedObjectDrawableChanged,
+    this.onPainterSettingsChanged,
+    this.onIsDrawingStateChanged,
+  })  : _builder = builder,
         super(key: key);
 
   @override
@@ -105,6 +111,7 @@ class FlutterPainter extends StatelessWidget {
                   onPainterSettingsChanged: onPainterSettingsChanged,
                   onSelectedObjectDrawableChanged:
                       onSelectedObjectDrawableChanged,
+                  onIsDrawingStateChanged: onIsDrawingStateChanged,
                 ));
           }),
     );
@@ -133,15 +140,19 @@ class _FlutterPainterWidget extends StatelessWidget {
   /// Callback when the [PainterSettings] of [PainterController] are updated internally.
   final ValueChanged<PainterSettings>? onPainterSettingsChanged;
 
+  /// Callback when a [FreeStyleDrawable] starts or stops being drawn
+  final ValueChanged<bool>? onIsDrawingStateChanged;
+
   /// Creates a [_FlutterPainterWidget] with the given [controller] and optional callbacks.
-  const _FlutterPainterWidget(
-      {Key? key,
-      required this.controller,
-      this.onDrawableCreated,
-      this.onDrawableDeleted,
-      this.onSelectedObjectDrawableChanged,
-      this.onPainterSettingsChanged})
-      : super(key: key);
+  const _FlutterPainterWidget({
+    Key? key,
+    required this.controller,
+    this.onDrawableCreated,
+    this.onDrawableDeleted,
+    this.onSelectedObjectDrawableChanged,
+    this.onPainterSettingsChanged,
+    this.onIsDrawingStateChanged,
+  }) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -197,6 +208,8 @@ class _FlutterPainterWidget extends StatelessWidget {
       onSelectedObjectDrawableChanged?.call(notification.drawable);
     } else if (notification is SettingsUpdatedNotification) {
       onPainterSettingsChanged?.call(notification.settings);
+    } else if (notification is DrawableIsDrawingStateChangedNotification) {
+      onIsDrawingStateChanged?.call(notification.isDrawing);
     }
     return true;
   }

lib/src/views/widgets/free_style_widget.dart

@@ -35,6 +35,7 @@ class _FreeStyleWidgetState extends State<_FreeStyleWidget> {
             onHorizontalDragDown: _handleHorizontalDragDown,
             onHorizontalDragUpdate: _handleHorizontalDragUpdate,
             onHorizontalDragUp: _handleHorizontalDragUp,
+            onHorizontalDragCancel: _handleHorizontalDragCancel,
           ),
           (_) {},
         ),
@@ -82,6 +83,9 @@ class _FreeStyleWidgetState extends State<_FreeStyleWidget> {
 
     // Set the drawable as the current drawable
     this.drawable = drawable;
+
+    // notify that we now start drawing
+    DrawableIsDrawingStateChangedNotification(true).dispatch(context);
   }
 
   /// Callback when the user moves, rotates or scales the pointer(s).
@@ -105,11 +109,24 @@ class _FreeStyleWidgetState extends State<_FreeStyleWidget> {
   /// Callback when the user removes all pointers from the widget.
   void _handleHorizontalDragUp() {
     DrawableCreatedNotification(drawable).dispatch(context);
+    // notify that we now start drawing
+    DrawableIsDrawingStateChangedNotification(false).dispatch(context);
 
     /// Reset the current drawable for the user to draw a new one next time
     drawable = null;
   }
 
+  /// Callback when the pointer event was falsely directed to us.
+  /// E.g. when the wrist was layed on the pad, but then a pen is recognized.
+  /// => the painting input of the wrist is invalid!
+  void _handleHorizontalDragCancel() {
+    if (drawable != null && drawable is PathDrawable) {
+      PainterController.of(context).removeDrawable(drawable!);
+    }
+    drawable = null;
+    DrawableIsDrawingStateChangedNotification(false).dispatch(context);
+  }
+
   Offset _globalToLocal(Offset globalPosition) {
     final getBox = context.findRenderObject() as RenderBox;
 
@@ -123,11 +140,13 @@ class _DragGestureDetector extends OneSequenceGestureRecognizer {
     required this.onHorizontalDragDown,
     required this.onHorizontalDragUpdate,
     required this.onHorizontalDragUp,
+    required this.onHorizontalDragCancel,
   });
 
   final ValueSetter<Offset> onHorizontalDragDown;
   final ValueSetter<Offset> onHorizontalDragUpdate;
   final VoidCallback onHorizontalDragUp;
+  final VoidCallback onHorizontalDragCancel;
 
   bool _isTrackingGesture = false;
 
@@ -152,6 +171,10 @@ class _DragGestureDetector extends OneSequenceGestureRecognizer {
       onHorizontalDragUp();
       stopTrackingPointer(event.pointer);
       _isTrackingGesture = false;
+    } else if (event is PointerCancelEvent) {
+      onHorizontalDragCancel();
+      stopTrackingPointer(event.pointer);
+      _isTrackingGesture = false;
     }
   }