[Impeller] Texture sampling seems to behave differently between Skia and Impeller (iOS) #115039
Description
Besides the issue with the texture background sometimes being black, the child appears distored under impeller differently than it would be under Skia:
Skia:
Impeller:
main.dart
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter_shaders/flutter_shaders.dart';
void main() {
runApp(const MyApp());
}
final transform = Matrix4.identity().storage;
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({super.key, required this.title});
final String title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: RepaintBoundary(
child: ShaderBuilder(
(BuildContext context, FragmentShader shader, Widget? child) {
return AnimatedSampler(
(ui.Image image, Size size, Offset offset, ui.Canvas canvas) {
canvas.translate(offset.dx, offset.dy);
var sampler = ImageShader(image, TileMode.clamp, TileMode.clamp, transform);
shader.setFloat(0, size.width);
shader.setFloat(1, size.height);
shader.setSampler(0, sampler);
canvas.translate(offset.dx, offset.dy);
canvas.drawRect(Offset.zero & size, Paint()..shader = shader);
},
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headlineMedium,
),
],
),
);
},
assetKey: 'shaders/blur.frag',
),
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: const Icon(Icons.add),
),
);
}
}shaders/sampler.frag
precision highp float;
#include <flutter/runtime_effect.glsl>
const float PI = 3.14159;
layout(location = 0) uniform float width;
layout(location = 1) uniform float height;
layout(location = 2) uniform sampler2D tInput;
out vec4 fragColor;
float random(vec3 xyz){
return fract(sin(dot(xyz, vec3(12.9898, 78.233, 151.7182))) * 43758.5453);
}
vec4 fragment(vec2 uv, vec2 fragCoord) {
vec4 color = vec4(0.0);
float total = 0.0;
vec2 tDelta = 50 * vec2(cos(PI), sin(PI));
float offset = random(vec3(fragCoord, 1000.0));
for (float t = -30.0; t <= 30.0; t += 5){
float percent = (t + offset - 0.5) / 30.0;
float weight = 1.0 - abs(percent);
color += texture(tInput, uv + tDelta * percent) * weight;
total += weight;
}
if (total == 0.0) {
total = 1.0;
}
return color / total;
}
void main() {
vec2 pos = FlutterFragCoord();
vec2 uv = pos / vec2(width, height);
fragColor = fragment(uv, pos);
}
pubspec.yaml
name: foo_bar_shaders
description: A new Flutter project.
environment:
sdk: '>=2.19.0-374.0.dev <3.0.0'
dependencies:
flutter:
sdk: flutter
flutter_shaders: ^0.0.1
cupertino_icons: ^1.0.2
dev_dependencies:
flutter_test:
sdk: flutter
flutter_lints: ^2.0.0
flutter:
shaders:
- shaders/blur.frag
- shaders/sampler.frag