Scrolling Parallax in Flutter

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.

You may also check our Flutter app development company page

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

const url =
    'https://docs.flutter.dev/cookbook/img-files/effects/parallax';

1 2	const url = 'https://docs.flutter.dev/cookbook/img-files/effects/parallax';

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(),
        ),
      ),
    );
  }
}

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

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 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,

country: location.place,

);

}

LocationListItems Class

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 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

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 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(

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

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 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

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 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

class Location {
  const Location({
    required this.name,
    required this.place,
    required this.imageUrl,
  });

  final String name;
  final String place;
  final String imageUrl;
}

class Location {

const Location({

required this.name,

required this.place,

required this.imageUrl,

});

final String name;

final String place;

final String imageUrl;

}

location list

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',
  ),
];

const locationsList = [

Location(

place: 'U.S.A',

imageUrl: '$url/01-mount-rushmore.jpg',

Location(

place: 'Singapore',

imageUrl: '$url/02-singapore.jpg',

Location(

place: 'Peru',

imageUrl: '$url/03-machu-picchu.jpg',

Location(

place: 'Switzerland',

imageUrl: '$url/04-vitznau.jpg',

Location(

place: 'Indonesia',

imageUrl: '$url/05-bali.jpg',

Location(

place: 'Mexico',

imageUrl: '$url/06-mexico-city.jpg',

];

Complete code

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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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,

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(

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(

place: 'U.S.A',

imageUrl: '$url/01-mount-rushmore.jpg',

Location(

place: 'Singapore',

imageUrl: '$url/02-singapore.jpg',

Location(

place: 'Peru',

imageUrl: '$url/03-machu-picchu.jpg',

Location(

place: 'Switzerland',

imageUrl: '$url/04-vitznau.jpg',

Location(

place: 'Indonesia',

imageUrl: '$url/05-bali.jpg',

Location(

place: 'Mexico',

imageUrl: '$url/06-mexico-city.jpg',

];

Image

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!!

Reference

For more blogs click here.

Deepak Kumar 27 April 2023

. . .

Discuss on Helpdesk

Scrolling Parallax in Flutter

Image Scrolling Parallax in Flutter:

Url

Parallax Class

LocationListItems Class

Parallax Flow Delegate

Parallax

Render Parallax

Location Class

location list

Complete code

Image

Conclusion

Reference

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