sliver_cross_axis_align.dart

import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';

class SliverCrossAxisAlign extends SingleChildRenderObjectWidget {
  final double alignment;

  const SliverCrossAxisAlign({
    super.key,
    required this.alignment,
    required Widget sliver,
  }) : super(child: sliver);

  @override
  RenderSliverCrossAxisAlign createRenderObject(BuildContext context) {
    return RenderSliverCrossAxisAlign(alignment);
  }

  @override
  void updateRenderObject(
    BuildContext context,
    RenderSliverCrossAxisAlign renderObject,
  ) {
    renderObject.alignment = alignment;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DoubleProperty("alignment", alignment));
  }
}

class RenderSliverCrossAxisAlign extends RenderSliver
    with RenderObjectWithChildMixin<RenderSliver> {
  double _alignment;

  RenderSliverCrossAxisAlign(this._alignment);

  double get alignment => _alignment;

  set alignment(double value) {
    if (_alignment == value) return;
    _alignment = value;
    markNeedsLayout();
  }

  @override
  void setupParentData(RenderObject child) {
    if (child.parentData is! SliverPhysicalParentData) {
      child.parentData = SliverPhysicalParentData();
    }
  }

  @override
  void performLayout() {
    final child = this.child;

    if (child == null) {
      geometry = SliverGeometry.zero;
      return;
    }

    child.layout(constraints, parentUsesSize: true);

    final childParentData = child.parentData! as SliverPhysicalParentData;
    final childGeometry = child.geometry!;
    final childExtent = childGeometry.crossAxisExtent;

    if (childExtent != null) {
      final crossAxisExtent = constraints.crossAxisExtent;
      final crossAxisOffset = (crossAxisExtent - childExtent) * _alignment;
      childParentData.paintOffset = Offset(crossAxisOffset, 0);
    }

    geometry = childGeometry;
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    final child = this.child;
    if (child == null) return;

    final childParentData = child.parentData! as SliverPhysicalParentData;
    context.paintChild(child, offset + childParentData.paintOffset);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DoubleProperty("alignment", alignment));
  }

  @override
  List<DiagnosticsNode> debugDescribeChildren() {
    return <DiagnosticsNode>[
      if (child != null) child!.toDiagnosticsNode(name: "child"),
    ];
  }

  @override
  bool hitTestChildren(SliverHitTestResult result,
      {required double mainAxisPosition, required double crossAxisPosition}) {
    final child = this.child;
    if (child == null) return false;
    final childParentData = child.parentData! as SliverPhysicalParentData;
    return child.hitTest(
      result,
      mainAxisPosition: mainAxisPosition,
      crossAxisPosition: crossAxisPosition - childParentData.paintOffset.dx,
    );
  }

  @override
  void applyPaintTransform(covariant RenderObject child, Matrix4 transform) {
    assert(child == this.child);
    final SliverPhysicalParentData childParentData =
        child.parentData! as SliverPhysicalParentData;
    childParentData.applyPaintTransform(transform);
  }
}