Skip to content

Instantly share code, notes, and snippets.

Last active February 19, 2021 15:07
Show Gist options
  • Save collinjackson/49c77ab2f68275e68f12e481c52eefd0 to your computer and use it in GitHub Desktop.
Save collinjackson/49c77ab2f68275e68f12e481c52eefd0 to your computer and use it in GitHub Desktop.
ColorFilter example
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
/// Applies a color filter before painting its child.
class ColorFiltered extends SingleChildRenderObjectWidget {
/// Creates a widget that color filters its child.
/// The [colorFilter] argument must not be null.
const ColorFiltered({
Key key,
@required this.colorFilter,
Widget child,
}) : assert(colorFilter != null),
super(key: key, child: child);
/// The color filter to apply to the existing painted content when painting the child.
final ColorFilter colorFilter;
RenderColorFiltered createRenderObject(BuildContext context) {
return RenderColorFiltered(colorFilter: colorFilter);
void updateRenderObject(BuildContext context, RenderColorFiltered renderObject) {
renderObject.colorFilter = colorFilter;
/// A composited layer that applies a color filter to its children.
class ColorFilterLayer extends ContainerLayer {
/// Creates a color filter layer.
@required ColorFilter colorFilter,
}) : _colorFilter = colorFilter;
/// The color filter to apply to the children.
/// The scene must be explicitly recomposited after this property is changed
/// (as described at [Layer]).
ColorFilter get colorFilter => _colorFilter;
ColorFilter _colorFilter;
set colorFilter(ColorFilter value) {
if (value != _colorFilter) {
_colorFilter = value;
ui.EngineLayer addToScene(ui.SceneBuilder builder, [ Offset layerOffset = ]) {
// TODO(jackson): We should use our colorFilter here.
// Unfortunately SceneBuilder doesn't support ColorFilter.matrix, only
// ColorFilters with a color and blend mode are supported. An engine
// update is required to support arbitrary color filters.
builder.pushColorFilter(, BlendMode.difference);
addChildrenToScene(builder, layerOffset);
return null; // this does not return an engine layer yet.
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
properties.add(DiagnosticsProperty<ColorFilter>('colorFilter', colorFilter));
/// Applies a color filter to the existing painted content and then paints [child].
class RenderColorFiltered extends RenderProxyBox {
/// Creates a color filter.
/// The [colorFilter] argument must not be null.
RenderColorFiltered({ RenderBox child, @required ColorFilter colorFilter })
: assert(colorFilter != null),
_colorFilter = colorFilter,
/// The color filter to apply to the existing painted content before painting
/// the child.
ColorFilter get colorFilter => _colorFilter;
ColorFilter _colorFilter;
set colorFilter(ColorFilter value) {
assert(value != null);
if (_colorFilter == value)
_colorFilter = value;
bool get alwaysNeedsCompositing => child != null;
void paint(PaintingContext context, Offset offset) {
if (child != null) {
context.pushLayer(ColorFilterLayer(colorFilter: _colorFilter), super.paint, offset);
void main() => runApp(MyApp());
// This is the standard "flutter create" sample app with a ColorFiltered added
class MyApp extends StatelessWidget {
// This widget is the root of your application.
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
home: MyHomePage(title: 'Flutter Demo Home Page'),
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
_MyHomePageState createState() => _MyHomePageState();
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return ColorFiltered(
colorFilter: ColorFilter.mode(,
BlendMode.values[_counter % BlendMode.values.length],
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the method, and use it to set our appbar title.
title: Text(widget.title),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
children: <Widget>[
'You have pushed the button this many times:',
style: Theme.of(context).textTheme.display1,
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment