In this blog, we are going to learn about Scrolling Parallax in a flutter.
As we know flutter widgets are built in modern frameworks. A screen in the flutter app is totally made up of widgets.
And here we are also going to start with the widget.
In this blog, we are going to implement the Scrolling Parallax. And how to use in flutter application.
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Image Scrolling Parallax in Flutter:
Basically, the use of Image Scrolling Parallax is when we scroll down the list of images then the images in the cells slowly scroll upward. This is known as the parallax.
Now we are going to start with the code implementation.
Url
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const url = 'https://docs.flutter.dev/cookbook/img-files/effects/parallax'; |
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import 'package:flutter/material.dart'; import 'package:flutter/rendering.dart'; const Color darkRed = Color.fromARGB(255, 18, 32, 47); void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); @override Widget build(BuildContext context) { return MaterialApp( theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkRed), debugShowCheckedModeBanner: false, home: const Scaffold( body: Center( child: ParallaxClass(), ), ), ); } } |
Parallax Class
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class ParallaxClass extends StatelessWidget { const ParallaxClass({ super.key, }); @override Widget build(BuildContext context) { return SingleChildScrollView( child: Column( children: [ for (final location in locationsList) LocationListItem( imageUrl: location.imageUrl, name: location.name, country: location.place, ), ], ), ); } } |
LocationListItems Class
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class LocationListItem extends StatelessWidget { final GlobalKey _backgroundImageKey = GlobalKey(); LocationListItem({ super.key, required this.imageUrl, required this.name, required this.country, }); final String imageUrl; final String name; final String country; @override Widget build(BuildContext context) { return Padding( padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 8), child: AspectRatio( aspectRatio: 16 / 9, child: ClipRRect( borderRadius: BorderRadius.circular(8), child: Stack( children: [ _buildBackground(context), _buildGradient(), _buildTitle(), ], ), ), ), ); } Widget _buildBackground(BuildContext context) { return Flow( delegate: ParallaxFlowDelegate( scrollable: Scrollable.of(context)!, listItemContext: context, backgroundImageKey: _backgroundImageKey, ), children: [ Image.network( imageUrl, key: _backgroundImageKey, fit: BoxFit.cover, ), ], ); } Widget _buildGradient() { return Positioned.fill( child: DecoratedBox( decoration: BoxDecoration( gradient: LinearGradient( colors: [Colors.transparent, Colors.black.withOpacity(0.7)], begin: Alignment.topCenter, end: Alignment.bottomCenter, stops: const [0.6, 0.95], ), ), ), ); } Widget _buildTitle() { return Positioned( left: 20, bottom: 20, child: Column( mainAxisSize: MainAxisSize.min, crossAxisAlignment: CrossAxisAlignment.start, children: [ Text( name, style: const TextStyle( color: Colors.white, fontSize: 20, fontWeight: FontWeight.bold, ), ), Text( country, style: const TextStyle( color: Colors.white, fontSize: 14, ), ), ], ), ); } } |
Parallax Flow Delegate
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class ParallaxFlowDelegate extends FlowDelegate { ParallaxFlowDelegate({ required this.scrollable, required this.listItemContext, required this.backgroundImageKey, }) : super(repaint: scrollable.position); final ScrollableState scrollable; final BuildContext listItemContext; final GlobalKey backgroundImageKey; @override BoxConstraints getConstraintsForChild(int i, BoxConstraints constraints) { return BoxConstraints.tightFor( width: constraints.maxWidth, ); } @override void paintChildren(FlowPaintingContext context) { // Calculate the position of this list item within the viewport. final scrollableBox = scrollable.context.findRenderObject() as RenderBox; final listItemBox = listItemContext.findRenderObject() as RenderBox; final listItemOffset = listItemBox.localToGlobal( listItemBox.size.centerLeft(Offset.zero), ancestor: scrollableBox); // Determine the percent position of this list item within the // scrollable area. final viewportDimension = scrollable.position.viewportDimension; final scrollFraction = (listItemOffset.dy / viewportDimension).clamp(0.0, 1.0); // Calculate the vertical alignment of the background // based on the scroll percent. final verticalAlignment = Alignment(0.0, scrollFraction * 2 - 1); // Convert the background alignment into a pixel offset for // painting purposes. final backgroundSize = (backgroundImageKey.currentContext!.findRenderObject() as RenderBox) .size; final listItemSize = context.size; final childRect = verticalAlignment.inscribe(backgroundSize, Offset.zero & listItemSize); // Paint the background. context.paintChild( 0, transform: Transform.translate(offset: Offset(0.0, childRect.top)).transform, ); } @override bool shouldRepaint(ParallaxFlowDelegate oldDelegate) { return scrollable != oldDelegate.scrollable || listItemContext != oldDelegate.listItemContext || backgroundImageKey != oldDelegate.backgroundImageKey; } } |
Parallax
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class Parallax extends SingleChildRenderObjectWidget { const Parallax({ super.key, required Widget background, }) : super(child: background); @override RenderObject createRenderObject(BuildContext context) { return RenderParallax(scrollable: Scrollable.of(context)!); } @override void updateRenderObject( BuildContext context, covariant RenderParallax renderObject) { renderObject.scrollable = Scrollable.of(context)!; } } |
Render Parallax
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class ParallaxParentData extends ContainerBoxParentData<RenderBox> {} class RenderParallax extends RenderBox with RenderObjectWithChildMixin<RenderBox>, RenderProxyBoxMixin { RenderParallax({ required ScrollableState scrollable, }) : _scrollable = scrollable; ScrollableState _scrollable; ScrollableState get scrollable => _scrollable; set scrollable(ScrollableState value) { if (value != _scrollable) { if (attached) { _scrollable.position.removeListener(markNeedsLayout); } _scrollable = value; if (attached) { _scrollable.position.addListener(markNeedsLayout); } } } @override void attach(covariant PipelineOwner owner) { super.attach(owner); _scrollable.position.addListener(markNeedsLayout); } @override void detach() { _scrollable.position.removeListener(markNeedsLayout); super.detach(); } @override void setupParentData(covariant RenderObject child) { if (child.parentData is! ParallaxParentData) { child.parentData = ParallaxParentData(); } } @override void performLayout() { size = constraints.biggest; // Force the background to take up all available width // and then scale its height based on the image's aspect ratio. final background = child!; final backgroundImageConstraints = BoxConstraints.tightFor(width: size.width); background.layout(backgroundImageConstraints, parentUsesSize: true); // Set the background's local offset, which is zero. (background.parentData as ParallaxParentData).offset = Offset.zero; } @override void paint(PaintingContext context, Offset offset) { // Get the size of the scrollable area. final viewportDimension = scrollable.position.viewportDimension; // Calculate the global position of this list item. final scrollableBox = scrollable.context.findRenderObject() as RenderBox; final backgroundOffset = localToGlobal(size.centerLeft(Offset.zero), ancestor: scrollableBox); // Determine the percent position of this list item within the // scrollable area. final scrollFraction = (backgroundOffset.dy / viewportDimension).clamp(0.0, 1.0); // Calculate the vertical alignment of the background // based on the scroll percent. final verticalAlignment = Alignment(0.0, scrollFraction * 2 - 1); // Convert the background alignment into a pixel offset for // painting purposes. final background = child!; final backgroundSize = background.size; final listItemSize = size; final childRect = verticalAlignment.inscribe(backgroundSize, Offset.zero & listItemSize); // Paint the background. context.paintChild( background, (background.parentData as ParallaxParentData).offset + offset + Offset(0.0, childRect.top)); } } |
Location Class
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class Location { const Location({ required this.name, required this.place, required this.imageUrl, }); final String name; final String place; final String imageUrl; } |
location list
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const locationsList = [ Location( name: 'Mount Rushmore', place: 'U.S.A', imageUrl: '$url/01-mount-rushmore.jpg', ), Location( name: 'Gardens By The Bay', place: 'Singapore', imageUrl: '$url/02-singapore.jpg', ), Location( name: 'Machu Picchu', place: 'Peru', imageUrl: '$url/03-machu-picchu.jpg', ), Location( name: 'Vitznau', place: 'Switzerland', imageUrl: '$url/04-vitznau.jpg', ), Location( name: 'Bali', place: 'Indonesia', imageUrl: '$url/05-bali.jpg', ), Location( name: 'Mexico City', place: 'Mexico', imageUrl: '$url/06-mexico-city.jpg', ), ]; |
Complete code
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import 'package:flutter/material.dart'; import 'package:flutter/rendering.dart'; const Color darkRed = Color.fromARGB(255, 18, 32, 47); void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); @override Widget build(BuildContext context) { return MaterialApp( theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkRed), debugShowCheckedModeBanner: false, home: const Scaffold( body: Center( child: ParallaxClass(), ), ), ); } } class ParallaxClass extends StatelessWidget { const ParallaxClass({ super.key, }); @override Widget build(BuildContext context) { return SingleChildScrollView( child: Column( children: [ for (final location in locationsList) LocationListItem( imageUrl: location.imageUrl, name: location.name, country: location.place, ), ], ), ); } } class LocationListItem extends StatelessWidget { final GlobalKey _backgroundImageKey = GlobalKey(); LocationListItem({ super.key, required this.imageUrl, required this.name, required this.country, }); final String imageUrl; final String name; final String country; @override Widget build(BuildContext context) { return Padding( padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 8), child: AspectRatio( aspectRatio: 16 / 9, child: ClipRRect( borderRadius: BorderRadius.circular(8), child: Stack( children: [ _buildBackground(context), _buildGradient(), _buildTitle(), ], ), ), ), ); } Widget _buildBackground(BuildContext context) { return Flow( delegate: ParallaxFlowDelegate( scrollable: Scrollable.of(context)!, listItemContext: context, backgroundImageKey: _backgroundImageKey, ), children: [ Image.network( imageUrl, key: _backgroundImageKey, fit: BoxFit.cover, ), ], ); } Widget _buildGradient() { return Positioned.fill( child: DecoratedBox( decoration: BoxDecoration( gradient: LinearGradient( colors: [Colors.transparent, Colors.black.withOpacity(0.7)], begin: Alignment.topCenter, end: Alignment.bottomCenter, stops: const [0.6, 0.95], ), ), ), ); } Widget _buildTitle() { return Positioned( left: 20, bottom: 20, child: Column( mainAxisSize: MainAxisSize.min, crossAxisAlignment: CrossAxisAlignment.start, children: [ Text( name, style: const TextStyle( color: Colors.white, fontSize: 20, fontWeight: FontWeight.bold, ), ), Text( country, style: const TextStyle( color: Colors.white, fontSize: 14, ), ), ], ), ); } } class ParallaxFlowDelegate extends FlowDelegate { ParallaxFlowDelegate({ required this.scrollable, required this.listItemContext, required this.backgroundImageKey, }) : super(repaint: scrollable.position); final ScrollableState scrollable; final BuildContext listItemContext; final GlobalKey backgroundImageKey; @override BoxConstraints getConstraintsForChild(int i, BoxConstraints constraints) { return BoxConstraints.tightFor( width: constraints.maxWidth, ); } @override void paintChildren(FlowPaintingContext context) { // Calculate the position of this list item within the viewport. final scrollableBox = scrollable.context.findRenderObject() as RenderBox; final listItemBox = listItemContext.findRenderObject() as RenderBox; final listItemOffset = listItemBox.localToGlobal( listItemBox.size.centerLeft(Offset.zero), ancestor: scrollableBox); // Determine the percent position of this list item within the // scrollable area. final viewportDimension = scrollable.position.viewportDimension; final scrollFraction = (listItemOffset.dy / viewportDimension).clamp(0.0, 1.0); // Calculate the vertical alignment of the background // based on the scroll percent. final verticalAlignment = Alignment(0.0, scrollFraction * 2 - 1); // Convert the background alignment into a pixel offset for // painting purposes. final backgroundSize = (backgroundImageKey.currentContext!.findRenderObject() as RenderBox) .size; final listItemSize = context.size; final childRect = verticalAlignment.inscribe(backgroundSize, Offset.zero & listItemSize); // Paint the background. context.paintChild( 0, transform: Transform.translate(offset: Offset(0.0, childRect.top)).transform, ); } @override bool shouldRepaint(ParallaxFlowDelegate oldDelegate) { return scrollable != oldDelegate.scrollable || listItemContext != oldDelegate.listItemContext || backgroundImageKey != oldDelegate.backgroundImageKey; } } class Parallax extends SingleChildRenderObjectWidget { const Parallax({ super.key, required Widget background, }) : super(child: background); @override RenderObject createRenderObject(BuildContext context) { return RenderParallax(scrollable: Scrollable.of(context)!); } @override void updateRenderObject( BuildContext context, covariant RenderParallax renderObject) { renderObject.scrollable = Scrollable.of(context)!; } } class ParallaxParentData extends ContainerBoxParentData<RenderBox> {} class RenderParallax extends RenderBox with RenderObjectWithChildMixin<RenderBox>, RenderProxyBoxMixin { RenderParallax({ required ScrollableState scrollable, }) : _scrollable = scrollable; ScrollableState _scrollable; ScrollableState get scrollable => _scrollable; set scrollable(ScrollableState value) { if (value != _scrollable) { if (attached) { _scrollable.position.removeListener(markNeedsLayout); } _scrollable = value; if (attached) { _scrollable.position.addListener(markNeedsLayout); } } } @override void attach(covariant PipelineOwner owner) { super.attach(owner); _scrollable.position.addListener(markNeedsLayout); } @override void detach() { _scrollable.position.removeListener(markNeedsLayout); super.detach(); } @override void setupParentData(covariant RenderObject child) { if (child.parentData is! ParallaxParentData) { child.parentData = ParallaxParentData(); } } @override void performLayout() { size = constraints.biggest; // Force the background to take up all available width // and then scale its height based on the image's aspect ratio. final background = child!; final backgroundImageConstraints = BoxConstraints.tightFor(width: size.width); background.layout(backgroundImageConstraints, parentUsesSize: true); // Set the background's local offset, which is zero. (background.parentData as ParallaxParentData).offset = Offset.zero; } @override void paint(PaintingContext context, Offset offset) { // Get the size of the scrollable area. final viewportDimension = scrollable.position.viewportDimension; // Calculate the global position of this list item. final scrollableBox = scrollable.context.findRenderObject() as RenderBox; final backgroundOffset = localToGlobal(size.centerLeft(Offset.zero), ancestor: scrollableBox); // Determine the percent position of this list item within the // scrollable area. final scrollFraction = (backgroundOffset.dy / viewportDimension).clamp(0.0, 1.0); // Calculate the vertical alignment of the background // based on the scroll percent. final verticalAlignment = Alignment(0.0, scrollFraction * 2 - 1); // Convert the background alignment into a pixel offset for // painting purposes. final background = child!; final backgroundSize = background.size; final listItemSize = size; final childRect = verticalAlignment.inscribe(backgroundSize, Offset.zero & listItemSize); // Paint the background. context.paintChild( background, (background.parentData as ParallaxParentData).offset + offset + Offset(0.0, childRect.top)); } } class Location { const Location({ required this.name, required this.place, required this.imageUrl, }); final String name; final String place; final String imageUrl; } const url = 'https://docs.flutter.dev/cookbook/img-files/effects/parallax'; const locationsList = [ Location( name: 'Mount Rushmore', place: 'U.S.A', imageUrl: '$url/01-mount-rushmore.jpg', ), Location( name: 'Gardens By The Bay', place: 'Singapore', imageUrl: '$url/02-singapore.jpg', ), Location( name: 'Machu Picchu', place: 'Peru', imageUrl: '$url/03-machu-picchu.jpg', ), Location( name: 'Vitznau', place: 'Switzerland', imageUrl: '$url/04-vitznau.jpg', ), Location( name: 'Bali', place: 'Indonesia', imageUrl: '$url/05-bali.jpg', ), Location( name: 'Mexico City', place: 'Mexico', imageUrl: '$url/06-mexico-city.jpg', ), ]; |
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Conclusion
In this blog, we have discussed how we can use the Scrolling Parallax in the flutter app.
I hope it will help you in understanding the Scrolling Parallax.
Thanks for reading!!
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