mirrored_repositories/get_wallpaper/lib/core
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

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));
  }
}
