Overview

Tremble is a lightweight Flutter game engine that follows the simple setup → update → draw pattern found in frameworks like p5.js, Processing, Raylib, and LÖVE. No complex architecture — just write a controller and draw to the canvas.

Lunapulse Showcase

A game built with Tremble + TECS. Play it on itch.io →

Watch Trailer

Setup

GameArea

The root widget. Wrap it with SizedBox + FittedBox for a fixed-resolution letterbox canvas.

DartFittedBox(
  child: SizedBox(
    width: 480,
    height: 640,
    child: GameArea(controller: DemoController()),
  ),
)

ScreenController

Dartclass DemoController extends ScreenController {
  void setup(BuildContext context, double width, double height) { }
  void resize(double width, double height) { }
  void update(double deltaTime) { }
  void draw(Canvas canvas, Size size) { }
  void lifecycleChanged(AppLifecycleState state) { }
  void dispose() { }
}

Lifecycle

lifecycleChanged is called when the app transitions between foreground and background. The AppLifecycleState values are resumed, inactive, paused, hidden, and detached. Use it to pause/resume game logic or audio.

Dartvoid lifecycleChanged(AppLifecycleState state) {
  if (state == AppLifecycleState.paused) {
    // pause music, save game state
  } else if (state == AppLifecycleState.resumed) {
    // resume music, refresh UI
  }
}

Preload

Load assets before the first frame. Report progress via the callback and call done():

DartFuture<void> preload(progress, done) async {
  progress(0.5);
  // await loadAssets();
  progress(1.0);
  done();
}

Show a loading UI with loadingBuilder:

DartGameArea(
  controller: DemoController(),
  loadingBuilder: (context, progress) =>
    Center(child: LinearProgressIndicator(value: progress)),
)

Input

Keyboard

Dartvoid keyDown(LogicalKeyboardKey key) { }
void keyUp(LogicalKeyboardKey key) { }

Hold detection via a Set:

Dartfinal keys = <LogicalKeyboardKey>{};

void update(double dt) {
  if (keys.contains(LogicalKeyboardKey.space)) { /* held */ }
}
void keyDown(LogicalKeyboardKey k) { keys.add(k); }
void keyUp(LogicalKeyboardKey k)   { keys.remove(k); }

Mouse

Dartvoid mouseMove(int id, double x, double y) { }
void mousePressed(int id, int button, double x, double y) { }
void mouseReleased(int id) { }
void mouseScroll(Offset scroll) { }

Rendering

SpriteBatch

Loads a GDX texture atlas and renders all sprites in a single draw call. Supports flipping and masking without canvas transforms.

Dartfinal batch = await SpriteBatch.fromGdxPacker(
  "assets/sprites.atlas",
  flippable: true,
  maskable: false,
);
// Custom: SpriteBatch.custom(image: ..., textures: ..., frames: ...)

final tex = batch.getTexture(Tex.table);
final anim = batch.getAnimation(Tex.marioBigRun, speed: 10);

batch.draw(canvas, [hero, table]);

// Generate enum code from atlas for debugging
batch.getEnum(); // → "enum Tex { marioBigIdle("Mario_Big_Idle", false), ... }"
batch.dispose(); // when done

Sprite

Dartfinal s = Sprite(
  texture: batch.getTexture(Tex.table),
  position: Vec2(100, 100),
);
s.originX = 0.5;  s.originY = 0.5;
s.opacity = 255;  s.scale = 1.0;
s.rotation = 0;   s.flip = false;
s.tint = Colors.white;
s.mask = false;

final copy = s.copy();
s.setFrom(copy);

Animation

Extends Sprite with frame-based animation, multiple states, and looping.

Dartenum HeroAnim {
  idle("hero-idle"),
  run("hero-run");

  const HeroAnim(this.assetName);
  final String assetName;

  @override
  String toString() => assetName;
}

final hero = Animation<HeroAnim>(
  animations: [
    batch.getAnimation(HeroAnim.idle, speed: 10),
    batch.getAnimation(HeroAnim.run,  speed: 10),
  ],
  position: Vec2(200, 300),
  speed: 1.0,
);

hero.update(deltaTime);
hero.setAnimation(HeroAnim.run, fromFrame: 0);
hero.resetAnimation(HeroAnim.run, fromFrame: 0);
hero.paused = false;
hero.speed = 0.5;  // internal speed multiplier (default 1.0)
hero.finished;       // true when a non-looping animation ends
hero.index;          // current frame index

AnimMode

Controls how the animation plays:

Set reverse: true to play any mode in reverse (e.g. playOnce stops at first frame instead of last).

AnimationData is returned by batch.getAnimation():

Dart// Data holds name + frames + base speed
final data = batch.getAnimation(HeroAnim.idle, speed: 10);

// Animation adds an internal speed multiplier
final hero = Animation<HeroAnim>(
  animations: [data],
  position: Vec2(200, 300),
  speed: 1.0,
  mode: AnimMode.loop,
);

// Change at runtime
hero.speed = 0.5;
hero.mode = AnimMode.pingPong;
hero.reverse = true;

CanvasText

Efficiently draws text on a Canvas without rebuilding the TextPainter on every frame. Update .text or .style and the painter is re-laid-out lazily on the next draw() call.

Dartfinal scoreText = CanvasText(
  text: 'Score: 0',
  style: const TextStyle(
    fontSize: 24,
    color: Colors.white,
    fontWeight: FontWeight.bold,
  ),
);

// Each frame
scoreText.draw(canvas, const Offset(20, 20));

// When score changes — automatically marks dirty
scoreText.text = 'Score: 100';

// Subsequent frames just draw without re-layout until text changes
scoreText.draw(canvas, const Offset(20, 20));

Supports TextDirection, TextAlign, and style setter — all trigger a lazy re-layout before the next paint.

Grid

A 2D grid backed by a flat List<T>. Generic — typically Grid<int> where each cell stores a tile ID (-1 = empty). Supports construction from 1D/2D data and tile coordinate conversion.

Dartfinal grid = Grid<int>(cellSize: 16, width: 20, height: 15, data: myData);
final grid2 = Grid<int>.filled(cellSize: 16, width: 20, height: 15, value: -1);
final grid3 = Grid<int>.from2d(cellSize: 16, data: [
  [0, 0, 1],
  [0, 2, 1],
]);

grid.cellSize;   // pixels per cell
grid.width;      // cells horizontally
grid.height;     // cells vertically

grid.tileAt2d(1, 2);  // tile ID at (x, y)
grid.tileAt1d(5);    // tile ID at flat index
grid.to1d(1, 2);      // → 2 * width + 1
grid.to2d(5);        // → (x, y)
grid.inBounds2d(1, 2); // true if within grid

grid.setTile2d(3, x: 1, y: 2);
grid.setTile1d(3, idx: 5);
grid.setTile2dScreen(3, x: 50.0, y: 30.0); // set by pixel coords

final copy = grid.clone();           // deep copy of the data
final (gx, gy) = grid.screenToGrid(50.0, 30.0); // pixel → grid coords

Neighbors

Bounds-safe neighbor access by flat index. hasNeighbor* returns whether that neighbor exists; *NeighborTile returns the neighbor tile value or null when out of bounds.

Dartgrid.hasNeighborLeft(idx);  grid.hasNeighborRight(idx);
grid.hasNeighborUp(idx);    grid.hasNeighborDown(idx);

grid.leftNeighborTile(idx);  // int? — null when out of bounds
grid.rightNeighborTile(idx);
grid.upNeighborTile(idx);    grid.downNeighborTile(idx);
grid.upLeftNeighborTile(idx);   grid.upRightNeighborTile(idx);
grid.downLeftNeighborTile(idx); grid.downRightNeighborTile(idx);

// Iterate neighbor indices without allocating (4 or 8 connected)
grid.forEachNeighbor4(idx, (n) { });
grid.forEachNeighbor8(idx, (n) { });

// Collect neighbor tile values (1 allocation)
final n4 = grid.neighborTiles4(idx);
final n8 = grid.neighborTiles8(idx);

Drawing

Drawing helpers live on the IntGridX extension for Grid<int>. Draw the grid through a TileMap or as flat debug rects. Tiles with a value smaller than 0 are skipped. position offsets the grid in world space and cullArea limits drawing to a viewport AABB.

Dart// Render through a TileMap
grid.draw(canvas, tilemap, position: Vec2(100, 0));

// Debug render — colored rects per tile (default debug palette, or pass one)
grid.debugDraw(canvas, cullArea: AABB(Vec2.zero(), width: 320, height: 240),
  palette: myPalette);

// Iterate visible tiles yourself
grid.forEachDrawArea(
  position: Vec2.zero(),
  visit: (screenX, screenY, tile) { /* custom render */ },
);

TileMap

Renders Grid layers efficiently using drawRawAtlas. Culls tiles outside a viewport AABB and supports multi-layer rendering (e.g. base + detail). Reusable buffers avoid per-frame allocations.

Dartfinal tilemap = TileMap(
  tileAreas: spriteSheet.split(count: 100, axis: Axis.horizontal),
  image: sheetImage,
);

// Single grid
tilemap.drawGrid(canvas, groundGrid, position: Vec2(100, 0));

// Multiple layers at once
tilemap.drawGrids(canvas, [baseGrid, decorGrid],
  position: Vec2(100, 0),
  cullArea: AABB(Vec2(0, 0), width: 320, height: 240),
);

Camera

Viewport transform with zoom, shake, and nesting support.

Dartfinal cam = Camera(zoom: 2, x: 100, y: 50);

void draw(Canvas canvas, Size size) {
  cam.start(canvas);
  // draw world-space content here
  cam.stop(canvas);
}

// Shake
cam.shake(
  wait: waitEvents,
  time: 0.3,
  amount: 4,
  slowlyHalt: true,
);

cam.reset(); // position → (0,0), zoom → 1

Tooling

Signals

A lightweight pub-sub system (inspired by Godot signals). Callbacks return true to keep listening or false to unsubscribe.

Dartfinal sig = Signal<int>();

sig.listen((v) { print(v); return true; });
sig.dispatch(42);

sig.unlisten(myFn);
sig.clear();
sig.length;

SignalValue

Reactive value holder. Setting value dispatches through an internal Signal. Automatically updates the stored value when the signal fires.

Dartfinal health = SignalValue<int>(100);

health.value = 80;  // dispatches through health.signal
health.signal;         // underlying Signal<int>
health.dispose();

SignalValueBuilder

Flutter widget that rebuilds when its SignalValue changes. onSignal return values: true rebuilds, false unsubscribes, null keeps listening without rebuild.

DartSignalValueBuilder<int>(
  value: health,
  builder: (context, child, val) => Text("$val"),
)

Wait Events

Timer utilities driven by your game loop. Call wait.update(dt) each frame.

Dartfinal wait = WaitEvents();

wait.wait(time: 1.5, onEnd: () { });
wait.waitAndDo(time: 2, onUpdate: (dt, remaining) { }, onEnd: () { });
wait.waitUntil(onUpdate: (dt) => alive, onEnd: () { });
wait.periodic(time: 1, onTick: (phase) { return true; }, onEnd: () { });

wait.update(deltaTime);
wait.clear();
wait.hasEvent;
wait.length;

WaitChain

Chain timed actions, animations, dialogs, and callbacks into a single sequential pipeline. Each step waits for the previous one to finish before starting.

Dartwait.chain()
  // 1. Snap the camera
  .run(() => camera.setPosition(0, 0))

  // 2. Smoothly zoom in over time
  .waitAndDo(1.5, (dt, remaining) {
    zoom = MathUtils.lerp(1.0, 2.0, 1.0 - remaining / 1.5);
  })

  // 3. Pan left until reaching a threshold
  .waitUntil((dt) {
    camera.x -= 40 * dt;
    return camera.x < -200;
  })

  // 4. Pause for dramatic effect
  .wait(1.0)

  // 5. Spawn entities and swap textures
  .run(() {
    world.spawn("debris", x: 120, y: 300);
    world.spawn("shockwave", x: 120, y: 300);
    bossSprite.texture = batch.getTexture(Tex.bossRage);
  })

  // 6. Wait for a dialog to finish (external callback)
  .blockUntil((continueFn) {
    dialog.show("You activated my trap card!", onEnd: continueFn);
  })

  // 7. Shake the camera briefly
  .waitAndDo(0.4, (dt, t) {
    camera.shake(4.0 * (t / 0.4));
  })

  .build();

The chain is driven by the same wait.update(dt) call — no extra plumbing needed.

State Machine

Generic typed FSM with enter / update / draw / exit hooks.

Dartfinal fsm = StateMachine<String>();

fsm.register("walking",
  onEnter:  () { },
  onUpdate: (dt) { },
  onExit:   () { },
  onDraw:   (c, s) { },
);

fsm.value = "walking";
fsm.previousState;
fsm.restart();
fsm.restart(triggerStateChange: true);
fsm.reset();
fsm.clear();

fsm.onBeforeStateChange = (from, to) { };
fsm.onAfterStateChange  = (from, to) { };

Physics

All shapes live under lib/physics/ and are re-exported from the main library. Shape is the abstract base — Circle, AABB, and Line extend it. RigidBody wraps a Shape with physics properties for dynamic simulation.

Shape

Abstract base class for all collision shapes. Each shape has a position and provides an aabb getter for broad-phase queries.

Dartabstract class Shape {
  Vec2 position;
  Shape clone();       // deep copy of the shape
  AABB get aabb;
  void draw(Canvas, Color);
}

Circle

Extends Shape. Positional constructor.

Dartfinal circle = Circle(
  Vec2(100, 100),
  radius: 30,
);

circle.x; circle.y; circle.radius; circle.radSq;
circle.aabb;  // → AABB
circle.clone();      // deep copy
circle.draw(canvas, color); // debug draw

AABB

Extends Shape. Axis-aligned bounding box.

Dartfinal box = AABB(
  Vec2(10, 20),
  width: 50,
  height: 80,
);

box.x; box.y; box.left; box.top; box.right; box.bottom;
box.rect;  // → Rect
box.inflated(5); box.deflated(5);
box.inflate(5); box.deflate(5);
box.clone();      // deep copy

Line

Extends Shape. p1 is an alias for position, p2 is the other endpoint.

Dartfinal line = Line(
  Vec2(0, 0),
  Vec2(100, 50),
);
line.p1;  // position
line.p2;  // endpoint
line.aabb; // bounding AABB

RigidBody

Wraps a Shape with physics properties for dynamic simulation. The shape field holds the geometry — position changes on the shape affect the body and vice versa.

Dartfinal body = RigidBody(
  shape: Circle(Vec2(100, 100), radius: 20),
  mass: 2.0,
  elasticity: 0.7,
  isStatic: false,
);

body.shape;         // → Shape (cast to Circle for radius access)
body.velocity;      // → Vec2
body.invMass;       // 0 if isStatic
body.applyImpulse(Vec2(50, 0));
body.update(deltaTime);  // advances position by velocity
body.copyWith(shape: ..., mass: ...);

CollisionDetector

Static detection methods. Works directly with the Shape types.

DartCollisionDetector.circleToCircle(circleA, circleB);
CollisionDetector.pointToCircle(point, circle);
CollisionDetector.rectToRect(boxA, boxB);
CollisionDetector.circleToRect(circle, box);
CollisionDetector.pointToRect(point, box);
CollisionDetector.pointToLine(point, line);
CollisionDetector.lineToLine(lineA, lineB);
CollisionDetector.lineToRect(line, box);
CollisionDetector.lineToCircle(line, circle);

// Dispatch on any two shapes automatically
CollisionDetector.shapeToShape(shapeA, shapeB); // works for AABB, Circle, Line

CollisionResolver

Static resolution methods. Penetration correction + impulse-based response for RigidBody collisions. No per-call allocations (uses internal temp Vec2s).

DartCollisionResolver.circleToCircle(bodyA, bodyB);
CollisionResolver.circleToStaticLine(body, line);

Each returns true if a collision occurred. Position is corrected based on invMass (static bodies don't move), and velocity is reflected with elasticity.

SpatialHash

Broad-phase spatial grid. Partitions space into cells to reduce collision checks — query only objects in nearby cells instead of all objects. No per-query allocations (reusable internal buffers).

Dartfinal hash = SpatialHash<RigidBody>(cellSize: 64);

// Each frame: rebuild or update
hash.clear();
for (final body in bodies) {
  hash.insert(body, body.shape.aabb);
}

// Query candidates for collision
for (final body in bodies) {
  final candidates = hash.query(body.shape.aabb);
  for (final other in candidates) {
    if (other == body) continue;
    // narrow-phase detection + resolution
  }
}

// Update a single moving body
hash.update(body, oldAABB, newAABB);

hash.cellCount;  // number of occupied cells

Using insert/remove/update avoids a full rebuild when only a few objects move.

Minkowski

Static methods for Minkowski difference and penetration vectors. Used for narrow-phase collision detection — if the origin is inside the difference shape, the shapes overlap.

Dartfinal diff = Minkowski.difference(aabbA, aabbB);
if (Minkowski.containsOrigin(diff)) {
  final pen = Minkowski.getPenetration(diff);
  // resolve with pen vector
}

Minkowski.differenceAABB(a, b);
Minkowski.differenceCircle(a, b);
Minkowski.differenceAABBAndCircle(a, b);
Minkowski.containsOriginAABB(aabb);
Minkowski.containsOriginCircle(circle);
Minkowski.getPenetrationAABB(aabb);
Minkowski.getPenetrationCircle(circle);

Sweep

Static helpers for swept collision detection. Expands a moving shape against a target shape, producing a volume you can raycast along the motion to find the time of impact. expand dispatches on the shape types automatically.

Dart// Dispatch on any shape pair (AABB + AABB / Circle + Circle / mixed)
final expanded = Sweep.expand(movingShape, targetShape);

// Typed variants
Sweep.expandAABB(movingAABB, targetAABB);          // → AABB
Sweep.expandCircle(movingCircle, targetCircle);      // → Circle
Sweep.expandAABBAndCircle(movingAABB, targetCircle);  // → AABB
Sweep.expandCircleAndAABB(movingCircle, targetAABB);  // → AABB

expand throws UnimplementedError for unsupported pairs (e.g. anything involving a Line).

Ray

A ray with an origin and unit-length direction. Direction is normalized on construction.

Dartfinal ray = Ray(origin: Vec2(0, 0), direction: Vec2(1, 0));

ray.pointAt(10);  // Vec2(10, 0)

Raycaster

Static raycast methods. Casts against circles, AABBs, lines, a spatial hash, or a tile grid. All return typed hit objects or null.

DartRaycastHit<Circle>? hit1 = Raycaster.raycastCircle(ray, circle);
RaycastHit<AABB>? hit2 = Raycaster.raycastAABB(ray, aabb);
RaycastHit<Line>? hit3 = Raycaster.raycastLine(ray, line);
RaycastHit<Shape>? hit4 = Raycaster.raycastShape(ray, shape);
RaycastHit<RigidBody>? hit5 = Raycaster.raycastSpatial(
  ray, hash, (body) => body.shape,
);

RaycastGridHit? hit6 = Raycaster.raycastGrid(
  ray,
  cellSize: 16,
  maxDistance: 200,
  isSolid: (tx, ty) => grid.isSolid(tx, ty),
);

Utilities

Vec2

Dartfinal v = Vec2(3, 4);
v.magnitude;             // 5
v.normalized();
v.distanceTo(other);
v.dot(other);
v.rotated(angle);
v.reflected(normal);
v.offset(dx: 5);   // → Offset

v + other;   v - other;
v * other;   v / other;    // Vec2 or scalar
-v;

v[0]; v[1];             // index access
v.add(other); v.sub(other);
v.scale(2);  v.setMag(10);

v.damp(target, lambda, deltaTime); // frame-rate independent smoothing
v.moveTowards(target, maxDelta);    // move toward target by at most maxDelta

Tween

Interpolates a double with a parametric curve.

Dartfinal t = Tween(0, 100, time: 2, curve: Parametrics.smoothStop2);

t.forward(startFrom: 0);
t.backward(startFrom: 1);
t.stop(stopAt: 0.5);
t.value;          // current interpolated value
t.ratio;          // current parametric t [0-1]
t.isTweening;
t.lastDirection;  // last direction if halted
t.changeTime(3);
t.update(deltaTime);

Spring

Physics-based spring simulation for smooth, natural motion. 1D for scalar values, 2D for positions.

Spring1D

Dartfinal s = Spring1D(initialValue: 0, stiffness: 180, damping: 12);
final s2 = Spring1D.critical(initialValue: 0, stiffness: 180);

s.value;          // current value
s.velocity;       // current velocity
s.update(dt, target);  // returns new value
s.snap(100);          // jump to value, zero velocity
s.isSettled(target);  // true if close to target and not moving

Spring2D

Dartfinal s = Spring2D(initialPos: Vec2(0, 0), stiffness: 180, damping: 12);
final s2 = Spring2D.critical(initialPos: Vec2.zero(), stiffness: 180);

s.pos;            // current position
s.velocity;       // current velocity (Vec2)
s.update(dt, target);  // returns new position
s.snap(Vec2(50, 100)); // jump to position, zero velocity
s.isSettled(target);   // true if close to target and not moving

critical constructor sets damping to 2√stiffness for critically damped motion (fastest settle without oscillation).

Second Order Dynamics

Spring-based smooth motion for cameras, UI, and character follow.

Dartfinal cam = SecondOrderDynamics.cameraSmooth(Vec2.zero());
final pos  = cam.update(deltaTime, target);
final pos2 = cam.update(deltaTime, target2);

ColorUtils

DartColorUtils.randomColor(ColorMood.bright);
ColorUtils.randomColor(ColorMood.pastel);
ColorUtils.randomColor(ColorMood.dark);
ColorUtils.randomHSV(mood, opacity: 0.8);

MathUtils

DartMathUtils.randInt(1, 10);
MathUtils.randDouble(0, 1);
MathUtils.randPick(list);
MathUtils.randTake(list);
MathUtils.randWeightedPick(list, weights);
MathUtils.randWeightedTake(list, weights);
MathUtils.flipCoin();
MathUtils.flipCoinWith(0.7);
MathUtils.shuffle(list);
MathUtils.seedRandom(42);

MathUtils.lerp(0, 10, 0.5);
MathUtils.inverseLerp(0, 10, 5);
MathUtils.remap(5, 0, 10, 100, 200);
MathUtils.constrain(15, 0, 10);
MathUtils.lcm(12, 18);
MathUtils.normalizeAngle(a);
MathUtils.lerpAngle(from, to, t);

MathUtils.moveTowards(current, target, maxDelta);
MathUtils.damp(current, target, lambda, deltaTime);

ImageUtils

DartImageUtils.loadImageFromBytes(bytes);
ImageUtils.loadImageFromAssets("img.png");
ImageUtils.loadImageFromPath("/path/img.png");
ImageUtils.generateFlipped(image);
ImageUtils.generateMasked(image);
ImageUtils.saveImage(image, "out.png");

Extensions

Dartrect.split(count: 4, axis: Axis.vertical);
rect.gridByCount(4, 3);
rect.gridBySize(16);
rect.aabb;    // → AABB

(3.14).fract;   // 0.14

// IntGridX — drawing/serialization for Grid<int>
grid.draw(canvas, tilemap);
grid.debugDraw(canvas);
grid.forEachDrawArea(position: Vec2.zero(), visit: (x, y, tile) { });
grid.toJson1d();  grid.toJson2d();

Helpers

DartHelpers.indexMapToList(indexedMap); // Map<int, T> → List<T>
Helpers.toCamelCase("Mario_Big_Run"); // → "marioBigRun"

FixedUpdate

Fixed time-step accumulator. Call update(dt) each frame with your variable delta — it runs your callback at a fixed rate (e.g. 60 times/second) regardless of frame timing. Useful for deterministic physics.

Dartfinal fixed = FixedUpdate(60, onUpdate: (fixedDt) {
  // called at exactly 60 fps worth of accumulated time
  physicsWorld.step(fixedDt);
});

// each frame
fixed.update(deltaTime);

// change rate at runtime
fixed.fps = 30;      // setter also updates fixedDeltaTime
fixed.fixedDeltaTime;  // → 1/30

Reference

Parametrics

All easing functions — type ParametricFunc = double Function(double t), where t is in [0, 1].

Linear

Smooth Start (ease-in)

Smooth Stop (ease-out)

Smooth Step (ease-in-out)

Special

Elastic (overshoot)

Utility

Vec2 API

Constructors

Properties

Instance Methods — immutable

Instance Methods — mutable

Operators

Static Methods

Second Order Dynamics Presets

Raw constructor: SecondOrderDynamics(f, z, r, initial) — frequency, damping, response.

WaitChainBuilder API

Each call returns the builder for fluent chaining. Finish with .build().

StateMachine API

Types

Darttypedef SubscriptionCallback<T>     = bool? Function(T);
typedef VoidCallback                = void Function();
typedef PeriodicCallback            = bool Function(int phase);
typedef UpdateCallback              = void Function(double dt);
typedef UpdateSubscriptionCallback  = bool Function(double dt);
typedef TimeUpdateCallback          = void Function(double dt, double remaining);
typedef StateChangeCallback<T>      = void Function(T? from, T? to);

Tremble — MIT License — GitHub