Scale - by Simon Lightfoot - 13th September 2023 - #HumpdayQandA

scale.dart

// MIT License
//
// Copyright (c) 2023 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//

import 'dart:ui' as ui;

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

/// Example of using [Scale] widget.
void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData.dark(useMaterial3: true),
      home: const Material(
        child: Scale(
          scale: 4.0,
          child: Padding(
            padding: EdgeInsets.all(24.0),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.stretch,
              children: [
                Text('Testing'),
                SizedBox(height: 8.0),
                AspectRatio(
                  aspectRatio: 4 / 1,
                  child: Placeholder(color: Colors.white),
                ),
              ],
            ),
          ),
        ),
      ),
    ),
  );
}

class Scale extends SingleChildRenderObjectWidget {
  const Scale({
    super.key,
    required this.scale,
    required super.child,
  });

  final double scale;

  @override
  RenderObject createRenderObject(BuildContext context) {
    return RenderScale(scale: scale);
  }

  @override
  void updateRenderObject(
    BuildContext context,
    covariant RenderScale renderObject,
  ) {
    renderObject.scale = scale;
  }
}

class RenderScale extends RenderProxyBox {
  RenderScale({
    required double scale,
  }) : _scale = scale;

  double _scale;

  double get scale => _scale;

  set scale(double value) {
    if (_scale == value) {
      return;
    }
    _scale = value;
    markNeedsLayout();
  }

  double get inverseScale => 1.0 / _scale;

  @override
  void performLayout() {
    final scaledConstraints = constraints * inverseScale;
    child!.layout(scaledConstraints, parentUsesSize: true);
    size = constraints.constrain(child!.size * _scale);
  }

  @override
  bool hitTestChildren(BoxHitTestResult result, {required Offset position}) {
    return child?.hitTest(result, position: position * inverseScale) ?? false;
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    final transform = Matrix4.diagonal3Values(_scale, _scale, 1.0);
    if (layer is TransformLayer) {
      final transformLayer = layer! as TransformLayer;
      transformLayer.transform = transform;
    } else {
      layer = TransformLayer(transform: transform);
    }
    context.pushLayer(layer!, super.paint, offset);
  }
}