What is the optimal render loop in Dart 2? - optimization

Question

I am looking for ideas regarding an optimal/minimal structure for the inner render loop in Dart 2, for a 2d game (if that part matters).
Clarification / Explanation: Every framework / language has an efficient way to:
1) Deal with time.
2) Render to the screen (via memory, a canvas, an image, or whatever).
For an example, here is someone that answered this for the C# language. Being new to Flutter / Dart, my first attempt (below), is failing to work and as of right now, I can not tell where the problem is.
I have searched high and low without finding any help on this, so if you can assist, you have my eternal gratitude.
There is a post on Reddit by ‘byu/inu-no-policemen’ (a bit old). I used this to start. I suspect that it is crushing the garbage collector or leaking memory.
This is what I have so far, but it crashes pretty quickly (at least in the debugger):
import 'dart:ui';
import 'dart:typed_data';
import 'dart:math' as math;
import 'dart:async';
main() async {
var deviceTransform = new Float64List(16)
..[0] = 1.0 // window.devicePixelRatio
..[5] = 1.0 // window.devicePixelRatio
..[10] = 1.0
..[15] = 1.0;
var previous = Duration.zero;
var initialSize = await Future<Size>(() {
if (window.physicalSize.isEmpty) {
var completer = Completer<Size>();
window.onMetricsChanged = () {
if (!window.physicalSize.isEmpty) {
completer.complete(window.physicalSize);
}
};
return completer.future;
}
return window.physicalSize;
});
var world = World(initialSize.width / 2, initialSize.height / 2);
window.onBeginFrame = (now) {
// we rebuild the screenRect here since it can change
var screenRect = Rect.fromLTWH(0.0, 0.0, window.physicalSize.width, window.physicalSize.height);
var recorder = PictureRecorder();
var canvas = Canvas(recorder, screenRect);
var delta = previous == Duration.zero ? Duration.zero : now - previous;
previous = now;
var t = delta.inMicroseconds / Duration.microsecondsPerSecond;
world.update(t);
world.render(t, canvas);
var builder = new SceneBuilder()
..pushTransform(deviceTransform)
..addPicture(Offset.zero, recorder.endRecording())
..pop();
window.render(builder.build());
window.scheduleFrame();
};
window.scheduleFrame();
window.onPointerDataPacket = (packet) {
var p = packet.data.first;
world.input(p.physicalX, p.physicalY);
};
}
class World {
static var _objectColor = Paint()..color = Color(0xa0a0a0ff);
static var _s = 200.0;
static var _obejectRect = Rect.fromLTWH(-_s / 2, -_s / 2, _s, _s);
static var _rotationsPerSecond = 0.25;
var _turn = 0.0;
double _x;
double _y;
World(this._x, this._y);
void input(double x, double y) { _x = x; _y = y; }
void update(double t) { _turn += t * _rotationsPerSecond; }
void render(double t, Canvas canvas) {
var tau = math.pi * 2;
canvas.translate(_x, _y);
canvas.rotate(tau * _turn);
canvas.drawRect(_obejectRect, _objectColor);
}
}

Answer 1

Well, after a month of beating my face against this, I finally figured out the right question and that got me to this:
Flutter Layers / Raw
// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This example shows how to perform a simple animation using the raw interface
// to the engine.
import 'dart:math' as math;
import 'dart:typed_data';
import 'dart:ui' as ui;
void beginFrame(Duration timeStamp) {
// The timeStamp argument to beginFrame indicates the timing information we
// should use to clock our animations. It's important to use timeStamp rather
// than reading the system time because we want all the parts of the system to
// coordinate the timings of their animations. If each component read the
// system clock independently, the animations that we processed later would be
// slightly ahead of the animations we processed earlier.
// PAINT
final ui.Rect paintBounds = ui.Offset.zero & (ui.window.physicalSize / ui.window.devicePixelRatio);
final ui.PictureRecorder recorder = ui.PictureRecorder();
final ui.Canvas canvas = ui.Canvas(recorder, paintBounds);
canvas.translate(paintBounds.width / 2.0, paintBounds.height / 2.0);
// Here we determine the rotation according to the timeStamp given to us by
// the engine.
final double t = timeStamp.inMicroseconds / Duration.microsecondsPerMillisecond / 1800.0;
canvas.rotate(math.pi * (t % 1.0));
canvas.drawRect(ui.Rect.fromLTRB(-100.0, -100.0, 100.0, 100.0),
ui.Paint()..color = const ui.Color.fromARGB(255, 0, 255, 0));
final ui.Picture picture = recorder.endRecording();
// COMPOSITE
final double devicePixelRatio = ui.window.devicePixelRatio;
final Float64List deviceTransform = Float64List(16)
..[0] = devicePixelRatio
..[5] = devicePixelRatio
..[10] = 1.0
..[15] = 1.0;
final ui.SceneBuilder sceneBuilder = ui.SceneBuilder()
..pushTransform(deviceTransform)
..addPicture(ui.Offset.zero, picture)
..pop();
ui.window.render(sceneBuilder.build());
// After rendering the current frame of the animation, we ask the engine to
// schedule another frame. The engine will call beginFrame again when its time
// to produce the next frame.
ui.window.scheduleFrame();
}
void main() {
ui.window.onBeginFrame = beginFrame;
ui.window.scheduleFrame();
}