feat: allow customize the backcard offset (#12)

CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## [5.0.0]
 
+- Adds option to customize the back card offset.
 - **BREAKING CHANGE**:
   - `CardSwiperController` is no longer disposed by `CardSwiper`, but who created it must dispose it.
 

example/lib/main.dart

@@ -42,9 +42,10 @@ class _ExamplePageState extends State<Example> {
               child: CardSwiper(
                 controller: controller,
                 cardsCount: cards.length,
-                numberOfCardsDisplayed: 3,
                 onSwipe: _onSwipe,
                 onUndo: _onUndo,
+                numberOfCardsDisplayed: 3,
+                backCardOffset: const Offset(40, 40),
                 padding: const EdgeInsets.all(24.0),
                 cardBuilder: (context, index) => cards[index],
               ),

lib/src/card_animation.dart

@@ -9,12 +9,15 @@ class CardAnimation {
     required this.animationController,
     required this.maxAngle,
     required this.initialScale,
+    required this.initialOffset,
     this.isHorizontalSwipingEnabled = true,
     this.isVerticalSwipingEnabled = true,
-  }) : scale = initialScale;
+  })  : scale = initialScale,
+        difference = initialOffset;
 
   final double maxAngle;
   final double initialScale;
+  final Offset initialOffset;
   final AnimationController animationController;
   final bool isHorizontalSwipingEnabled;
   final bool isVerticalSwipingEnabled;
@@ -24,12 +27,12 @@ class CardAnimation {
   double total = 0;
   double angle = 0;
   double scale;
-  double difference = 40;
+  Offset difference;
 
   late Animation<double> _leftAnimation;
   late Animation<double> _topAnimation;
   late Animation<double> _scaleAnimation;
-  late Animation<double> _differenceAnimation;
+  late Animation<Offset> _differenceAnimation;
 
   double get _maxAngleInRadian => maxAngle * (pi / 180);
 
@@ -47,7 +50,7 @@ class CardAnimation {
     total = 0;
     angle = 0;
     scale = initialScale;
-    difference = 40;
+    difference = initialOffset;
   }
 
   void update(double dx, double dy, bool inverseAngle) {
@@ -79,8 +82,13 @@ class CardAnimation {
   }
 
   void updateDifference() {
-    if (difference.isBetween(0, difference)) {
+    final discrepancy = (total > 0) ? total / 10 : -(total / 10);
-      difference = (total > 0) ? 40 - (total / 10) : 40 + (total / 10);
+
+    if (difference.dx.isBetween(0, initialOffset.dx)) {
+      difference = Offset(initialOffset.dx + discrepancy, difference.dy);
+    }
+    if (difference.dy.isBetween(0, initialOffset.dy)) {
+      difference = Offset(difference.dx, initialOffset.dy + discrepancy);
     }
   }
 
@@ -114,9 +122,9 @@ class CardAnimation {
       begin: scale,
       end: 1.0,
     ).animate(animationController);
-    _differenceAnimation = Tween<double>(
+    _differenceAnimation = Tween<Offset>(
       begin: difference,
-      end: 0,
+      end: Offset.zero,
     ).animate(animationController);
     animationController.forward();
   }
@@ -136,9 +144,9 @@ class CardAnimation {
       begin: scale,
       end: 1.0,
     ).animate(animationController);
-    _differenceAnimation = Tween<double>(
+    _differenceAnimation = Tween<Offset>(
       begin: difference,
-      end: 0,
+      end: Offset.zero,
     ).animate(animationController);
     animationController.forward();
   }
@@ -156,9 +164,9 @@ class CardAnimation {
       begin: scale,
       end: initialScale,
     ).animate(animationController);
-    _differenceAnimation = Tween<double>(
+    _differenceAnimation = Tween<Offset>(
       begin: difference,
-      end: 40,
+      end: initialOffset,
     ).animate(animationController);
     animationController.forward();
   }
@@ -193,8 +201,8 @@ class CardAnimation {
       begin: 1.0,
       end: scale,
     ).animate(animationController);
-    _differenceAnimation = Tween<double>(
+    _differenceAnimation = Tween<Offset>(
-      begin: 0,
+      begin: Offset.zero,
       end: difference,
     ).animate(animationController);
     animationController.forward();
@@ -215,8 +223,8 @@ class CardAnimation {
       begin: 1.0,
       end: scale,
     ).animate(animationController);
-    _differenceAnimation = Tween<double>(
+    _differenceAnimation = Tween<Offset>(
-      begin: 0,
+      begin: Offset.zero,
       end: difference,
     ).animate(animationController);
     animationController.forward();

lib/src/card_swiper.dart

@@ -106,6 +106,11 @@ class CardSwiper extends StatefulWidget {
   /// on top of the stack. If the function returns `true`, the undo action is performed as expected.
   final CardSwiperOnUndo? onUndo;
 
+  /// The offset of the back card from the front card.
+  ///
+  /// Must be a positive value. Defaults to Offset(0, 40).
+  final Offset backCardOffset;
+
   const CardSwiper({
     Key? key,
     required this.cardBuilder,
@@ -127,6 +132,7 @@ class CardSwiper extends StatefulWidget {
     this.isLoop = true,
     this.numberOfCardsDisplayed = 2,
     this.onUndo,
+    this.backCardOffset = const Offset(0, 40),
   })  : assert(
           maxAngle >= 0 && maxAngle <= 360,
           'maxAngle must be between 0 and 360',
@@ -151,6 +157,10 @@ class CardSwiper extends StatefulWidget {
           initialIndex >= 0 && initialIndex < cardsCount,
           'initialIndex must be between 0 and [cardsCount]',
         ),
+        assert(
+          backCardOffset >= Offset.zero,
+          'backCardOffset must be a positive value',
+        ),
         super(key: key);
 
   @override
@@ -194,6 +204,7 @@ class _CardSwiperState<T extends Widget> extends State<CardSwiper>
       initialScale: widget.scale,
       isVerticalSwipingEnabled: widget.isVerticalSwipingEnabled,
       isHorizontalSwipingEnabled: widget.isHorizontalSwipingEnabled,
+      initialOffset: widget.backCardOffset,
     );
   }
 
@@ -280,8 +291,8 @@ class _CardSwiperState<T extends Widget> extends State<CardSwiper>
 
   Widget _secondItem(BoxConstraints constraints) {
     return Positioned(
-      top: _cardAnimation.difference,
+      top: _cardAnimation.difference.dy,
-      left: 0,
+      left: _cardAnimation.difference.dx,
       child: Transform.scale(
         scale: _cardAnimation.scale,
         child: ConstrainedBox(
@@ -294,8 +305,8 @@ class _CardSwiperState<T extends Widget> extends State<CardSwiper>
 
   Widget _backItem(BoxConstraints constraints, int offset) {
     return Positioned(
-      top: 40,
+      top: widget.backCardOffset.dy,
-      left: 0,
+      left: widget.backCardOffset.dx,
       child: Transform.scale(
         scale: widget.scale,
         child: ConstrainedBox(

pubspec.yaml

@@ -2,7 +2,7 @@ name: flutter_card_swiper
 description: This is a Tinder-like card swiper package. It allows you to swipe left, right, up, and down and define your own business logic for each direction.
 homepage: https://github.com/ricardodalarme/flutter_card_swiper
 issue_tracker: https://github.com/ricardodalarme/flutter_card_swiper/issues
-version: 4.1.3
+version: 5.0.0
 
 environment:
   sdk: ">=2.12.0 <3.0.0"