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|
// A Mandelbrot explorer whose pixels are computed in Nim.
//
// What this is actually demonstrating:
// * bulk data across the FFI boundary — a full RGBA frame per render,
// into a buffer Dart allocates and Nim fills in place (nothing to nf_free)
// * band parallelism — the image is split into horizontal strips rendered
// on separate isolates, which is safe because the library is -gc none
// * the same algorithm written twice, in Nim and in Dart, so the cost of the
// bridge is a number on screen rather than a claim
import 'dart:async';
import 'dart:math' as math;
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:nimflutter_ffi/nimflutter_ffi.dart' as v;
import 'mandelbrot_dart.dart';
void main() => runApp(const ExampleApp());
class ExampleApp extends StatelessWidget {
const ExampleApp({super.key});
@override
Widget build(BuildContext context) => MaterialApp(
title: 'nimflutter_ffi',
debugShowCheckedModeBanner: false,
theme: ThemeData.dark(useMaterial3: true).copyWith(
scaffoldBackgroundColor: const Color(0xFF12141A),
),
home: const ExplorerPage(),
);
}
class ExplorerPage extends StatefulWidget {
const ExplorerPage({super.key});
@override
State<ExplorerPage> createState() => _ExplorerPageState();
}
/// Identifies the interactive canvas, so tests can drive gestures on it
/// without depending on whether a frame has finished rendering yet.
const Key canvasKey = Key('fractal-canvas');
class _ExplorerPageState extends State<ExplorerPage> {
static const int _renderWidth = 720;
static const int _renderHeight = 540;
v.FractalView _view = const v.FractalView(
width: _renderWidth,
height: _renderHeight,
maxIter: 400,
);
ui.Image? _image;
bool _rendering = false;
bool _renderQueued = false;
int _lastMs = 0;
int _tiles = 16;
_Benchmark? _benchmark;
String? _bootError;
/// Bands run on isolates natively and sequentially on web, so the word the
/// UI uses for them has to follow the backend.
String get _unit =>
v.supportsIsolateParallelism ? v.parallelUnitName : 'band';
@override
void initState() {
super.initState();
_boot();
}
/// Brings the bridge up and draws the first frame.
Future<void> _boot() => _render();
/// Waits for the bridge, returning false if it could not be brought up.
///
/// On native this resolves immediately. On web it is where the wasm module
/// is fetched and instantiated, which cannot be synchronous.
///
/// Every path that asks for a frame goes through here, not just startup:
/// the first layout pass calls _fitToCanvas -> _render before initState's
/// future has resolved, so gating only the boot path would still let the
/// very first render race the module load. initialize() is idempotent and
/// hands back the in-flight future, so the extra calls just wait.
Future<bool> _ensureReady() async {
if (v.isInitialized) return true;
try {
await v.initialize();
return true;
} catch (e) {
if (mounted) setState(() => _bootError = '$e');
return false;
}
}
@override
void dispose() {
_image?.dispose();
super.dispose();
}
/// Renders the current view, coalescing requests that arrive mid-frame.
///
/// A wheel gesture emits far more events than we can render. Dropping them
/// outright would leave the view mutated but never drawn, so instead the
/// latest request is remembered and serviced once the in-flight frame lands.
Future<void> _render() async {
if (!await _ensureReady()) return;
if (_rendering) {
_renderQueued = true;
return;
}
setState(() => _rendering = true);
do {
_renderQueued = false;
final view = _view;
final watch = Stopwatch()..start();
final pixels = _tiles > 1
? await v.renderParallel(view, tiles: _tiles)
: v.render(view);
watch.stop();
final image = await _decode(pixels, view.width, view.height);
if (!mounted) {
image.dispose();
return;
}
setState(() {
_image?.dispose();
_image = image;
_lastMs = watch.elapsedMilliseconds;
});
} while (_renderQueued);
if (!mounted) return;
setState(() => _rendering = false);
}
static Future<ui.Image> _decode(Uint8List rgba, int w, int h) {
final completer = Completer<ui.Image>();
ui.decodeImageFromPixels(rgba, w, h, ui.PixelFormat.rgba8888,
completer.complete);
return completer.future;
}
/// Drags the view by a pixel delta, so the image follows the cursor.
void _panBy(Offset delta, Size widgetSize) {
if (widgetSize.isEmpty || delta == Offset.zero) return;
setState(() {
_view = _view.pannedBy(
delta.dx / widgetSize.width,
delta.dy / widgetSize.height,
);
});
_render();
}
/// Zooms about a point, keeping that point under the cursor.
void _zoomAt(Offset local, Size widgetSize, double factor) {
if (widgetSize.isEmpty) return;
setState(() {
_view = _view.zoomedAt(
local.dx / widgetSize.width,
local.dy / widgetSize.height,
factor,
);
});
_render();
}
/// Restores the starting framing.
///
/// Only the pan/zoom is reset. Width and height belong to the canvas (see
/// _fitToCanvas) and maxIter belongs to its slider — clobbering those made
/// "Reset view" silently undo settings the button does not own, and briefly
/// render at the wrong aspect ratio before the canvas corrected it.
void _reset() {
const home = v.FractalView(width: 1, height: 1);
setState(() {
_view = _view.copyWith(
centerX: home.centerX,
centerY: home.centerY,
scale: home.scale,
);
});
_render();
}
/// Renders the identical frame in Nim and in Dart on this isolate, so the
/// comparison is like-for-like rather than Nim-plus-parallelism vs Dart.
Future<void> _runBenchmark() async {
if (!await _ensureReady()) return;
setState(() {
_rendering = true;
_benchmark = null;
});
final swV = Stopwatch()..start();
v.render(_view);
swV.stop();
final swP = Stopwatch()..start();
await v.renderParallel(_view, tiles: _tiles);
swP.stop();
final swD = Stopwatch()..start();
renderDart(_view);
swD.stop();
if (!mounted) return;
setState(() {
_rendering = false;
_benchmark = _Benchmark(
unit: _unit,
parallel: v.supportsIsolateParallelism,
vSerialMs: swV.elapsedMilliseconds,
vParallelMs: swP.elapsedMilliseconds,
dartMs: swD.elapsedMilliseconds,
tiles: _tiles,
);
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: LayoutBuilder(
builder: (context, constraints) {
final wide = constraints.maxWidth > 900;
final canvas = _buildCanvas();
final controls = _buildControls();
return wide
? Row(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
Expanded(child: canvas),
SizedBox(
width: 340,
child: SingleChildScrollView(child: controls),
),
],
)
: ListView(
children: [
AspectRatio(
aspectRatio: _renderWidth / _renderHeight,
child: canvas,
),
controls,
],
);
},
),
),
);
}
/// Keeps the rendered buffer at the canvas's aspect ratio.
///
/// Without this the image would be letterboxed or cropped, and the
/// click-to-zoom maths — which maps widget coordinates straight into the
/// complex plane — would point at the wrong place.
void _fitToCanvas(Size size) {
if (size.isEmpty) return;
final height = (_renderWidth * size.height / size.width).round();
if ((height - _view.height).abs() <= 2) return;
WidgetsBinding.instance.addPostFrameCallback((_) {
if (!mounted) return;
setState(() => _view = _view.copyWith(height: height));
_render();
});
}
Widget _buildCanvas() {
return LayoutBuilder(
builder: (context, constraints) {
final size = Size(constraints.maxWidth, constraints.maxHeight);
_fitToCanvas(size);
return Listener(
key: canvasKey,
// Wheel zoom, anchored at the cursor like the tap zoom. One notch is
// a small step so a scroll feels continuous rather than octave-wise;
// the render loop coalesces whatever it cannot keep up with.
onPointerSignal: (event) {
if (event is! PointerScrollEvent) return;
final dy = event.scrollDelta.dy;
if (dy == 0) return;
_zoomAt(event.localPosition, size, math.pow(1.0015, dy).toDouble());
},
child: GestureDetector(
// Zoom on tap up rather than tap down. The gesture arena already
// keeps onTapDown from firing once a pan claims the pointer, so
// this is not what makes drag-to-pan work — it just means the
// zoom commits on a completed tap.
onTapUp: (d) => _zoomAt(d.localPosition, size, 0.5),
onSecondaryTapUp: (d) => _zoomAt(d.localPosition, size, 2.0),
onPanUpdate: (d) => _panBy(d.delta, size),
child: Stack(
fit: StackFit.expand,
children: [
if (_bootError != null)
// Most likely on web: the wasm glue did not load, so there is
// no Nim to call. Say so rather than spinning forever.
Center(
child: Padding(
padding: const EdgeInsets.all(24),
child: Text(
'Could not start the Nim bridge.\n\n$_bootError',
textAlign: TextAlign.center,
style: Theme.of(context).textTheme.bodySmall,
),
),
)
else if (_image != null)
RawImage(image: _image, fit: BoxFit.fill)
else
const Center(child: CircularProgressIndicator()),
Positioned(
left: 12,
bottom: 12,
child: _Chip(
'zoom ${(3.0 / _view.scale).toStringAsFixed(1)}x · '
'$_lastMs ms · '
'${_tiles > 1 ? "$_tiles ${_unit}s" : "1 $_unit"}',
),
),
if (_rendering)
const Positioned(
right: 12,
top: 12,
child: SizedBox(
width: 18,
height: 18,
child: CircularProgressIndicator(strokeWidth: 2),
),
),
],
),
),
);
},
);
}
/// Returns a non-scrolling column.
///
/// The wide layout wraps this in its own scroll view; the narrow layout
/// embeds it in the page's ListView. Making this a ListView itself would
/// nest two scrollables and give the inner one unbounded height.
Widget _buildControls() {
final theme = Theme.of(context);
return Padding(
padding: const EdgeInsets.all(20),
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
Text('Mandelbrot in Nim', style: theme.textTheme.titleLarge),
const SizedBox(height: 4),
Text(
'Scroll or tap to zoom in, right-click to zoom out, drag to pan. '
'Every pixel is computed by nf_mandelbrot in src/nimflutter.v.',
style: theme.textTheme.bodySmall,
),
const SizedBox(height: 20),
_Labelled(
label: 'iterations',
value: '${_view.maxIter}',
child: Slider(
value: _view.maxIter.toDouble(),
min: 50,
max: 2000,
divisions: 39,
onChanged: (n) =>
setState(() => _view = _view.copyWith(maxIter: n.round())),
onChangeEnd: (_) => _render(),
),
),
_Labelled(
label: '${_unit}s',
value: '$_tiles',
child: Slider(
value: _tiles.toDouble(),
min: 1,
// Deliberately well past the core count. Bands cost wildly
// different amounts — rows through the set's interior run the full
// iteration cap, rows in open space escape immediately — so the
// frame waits on its slowest band. Over-decomposing lets a free
// core pick up the next small band instead of idling. Measured on
// an 8-thread machine: 8 tiles 44 ms, 24 tiles 29 ms.
max: 32,
divisions: 31,
onChanged: (n) => setState(() => _tiles = n.round()),
onChangeEnd: (_) => _render(),
),
),
const SizedBox(height: 8),
Row(
children: [
Expanded(
child: FilledButton.tonal(
onPressed: _rendering ? null : _reset,
child: const Text('Reset view'),
),
),
const SizedBox(width: 12),
Expanded(
child: FilledButton(
onPressed: _rendering ? null : _runBenchmark,
child: const Text('Benchmark'),
),
),
],
),
const SizedBox(height: 20),
if (_benchmark != null) _BenchmarkCard(result: _benchmark!),
const SizedBox(height: 12),
Card(
color: theme.colorScheme.surfaceContainerHighest,
child: Padding(
padding: const EdgeInsets.all(14),
child: Text(
v.backendName == 'dart:ffi'
? 'The Nim kernel fills a buffer Dart allocates, so no Nim '
'memory crosses the boundary and there is nothing to '
'free. Bands are independent, which is what makes the '
'isolate slider safe: ARC has no stop-the-world phase '
'to serialise them.'
: 'The same Nim kernel, compiled to WebAssembly and reached '
'over dart:js_interop instead of dart:ffi — it fills a '
'buffer in the wasm heap, so nothing needs freeing on '
'the Dart side. Each Web Worker holds its own instance '
'of the module, so nothing is shared and no '
'SharedArrayBuffer or COOP/COEP headers are needed. The '
'frame is identical to the native build, byte for byte.',
style: theme.textTheme.bodySmall,
),
),
),
],
),
);
}
}
class _Benchmark {
const _Benchmark({
required this.vSerialMs,
required this.vParallelMs,
required this.dartMs,
required this.tiles,
required this.unit,
required this.parallel,
});
final int vSerialMs;
final int vParallelMs;
final int dartMs;
final int tiles;
/// 'isolate' natively, 'band' on web.
final String unit;
/// Whether the split actually ran concurrently.
final bool parallel;
}
class _BenchmarkCard extends StatelessWidget {
const _BenchmarkCard({required this.result});
final _Benchmark result;
@override
Widget build(BuildContext context) {
final theme = Theme.of(context);
final ratio = result.dartMs / result.vSerialMs;
return Card(
child: Padding(
padding: const EdgeInsets.all(14),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text('same frame, three ways',
style: theme.textTheme.titleSmall),
const SizedBox(height: 10),
_Row(label: 'Nim, 1 ${result.unit}', value: '${result.vSerialMs} ms'),
_Row(
label: 'Nim, ${result.tiles} ${result.unit}s',
value: '${result.vParallelMs} ms'),
_Row(label: 'Dart, 1 ${result.unit}', value: '${result.dartMs} ms'),
const Divider(height: 20),
Text(
result.parallel
? 'Nim is ${ratio.toStringAsFixed(2)}x Dart on one isolate. '
'For a scalar FP loop the two are close — the real win '
'here is the parallel split, which Dart could also do. '
'The bridge is what this demonstrates, not a speed claim.'
: 'Nim is ${ratio.toStringAsFixed(2)}x Dart on one thread. '
'The wasm module is single-threaded, so the '
'${result.tiles}-band row above is the same work done '
'in sequence, not in parallel — it is here to show the '
'split produces identical pixels either way.',
style: theme.textTheme.bodySmall,
),
],
),
),
);
}
}
class _Row extends StatelessWidget {
const _Row({required this.label, required this.value});
final String label;
final String value;
@override
Widget build(BuildContext context) => Padding(
padding: const EdgeInsets.symmetric(vertical: 2),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
Text(label, style: Theme.of(context).textTheme.bodyMedium),
Text(value,
style: Theme.of(context)
.textTheme
.bodyMedium
?.copyWith(fontFeatures: const [ui.FontFeature.tabularFigures()])),
],
),
);
}
class _Labelled extends StatelessWidget {
const _Labelled({
required this.label,
required this.value,
required this.child,
});
final String label;
final String value;
final Widget child;
@override
Widget build(BuildContext context) {
final theme = Theme.of(context);
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
Text(label, style: theme.textTheme.labelLarge),
Text(value, style: theme.textTheme.labelLarge),
],
),
child,
],
);
}
}
class _Chip extends StatelessWidget {
const _Chip(this.text);
final String text;
@override
Widget build(BuildContext context) => Container(
padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 6),
decoration: BoxDecoration(
color: Colors.black.withValues(alpha: 0.55),
borderRadius: BorderRadius.circular(8),
),
child: Text(text,
style: const TextStyle(color: Colors.white, fontSize: 12)),
);
}
|