flutter_spritesheet_animation

flutter_spritesheet_animation

Lightweight spritesheet animation widget for Flutter. Supports grid-based and JSON atlas (TexturePacker, Aseprite) spritesheets with named animations, playback modes, and an external controller.

Zero external dependencies - uses only the Flutter SDK.

Features

• Grid-based spritesheet animation (uniform frame grid)
• JSON atlas animation (TexturePacker hash/array, Aseprite)
• Named animations via frameTags
• Playback modes: forward, reverse, pingPong
• External controller for programmatic control
• Per-frame duration support from atlas data
• Pre-computed frame rects for optimal rendering
• Configurable FPS, looping, blend mode, box fit
• Speed multiplier that also works on atlas animations with per-frame durations
• Fixed repeat counts with per-cycle callbacks

Installation

dependencies:
  flutter_spritesheet_animation: ^1.0.2

Usage

Grid Mode

For spritesheets with frames arranged in a uniform grid:

SpriteAnimation.grid(
  image: AssetImage('assets/explosion.png'),
  columns: 8,
  rows: 4,
  frameCount: 30,  // optional, defaults to columns * rows
  fps: 24,
  width: 128,
  height: 128,
)

Atlas Mode

For spritesheets defined by a JSON atlas (TexturePacker or Aseprite export):

// Load atlas from asset
final atlas = await SpriteAtlas.fromAsset('assets/character.json');

SpriteAnimation.atlas(
  image: AssetImage('assets/character.png'),
  atlas: atlas,
  animation: 'idle',  // named animation from frameTags
  width: 128,
  height: 128,
)

Controller

Use SpriteAnimationController for programmatic playback control:

final controller = SpriteAnimationController(
  fps: 24,
  mode: PlayMode.pingPong,
  loop: true,
  autoPlay: false,
);

// In your widget tree
SpriteAnimation.grid(
  image: AssetImage('assets/explosion.png'),
  columns: 8,
  rows: 4,
  controller: controller,
)

// Control playback
controller.play();
controller.pause();
controller.stop();
controller.goToFrame(5);

// Change settings at runtime
controller.fps = 30;
controller.mode = PlayMode.reverse;
controller.loop = false;

// Switch named animations (atlas mode)
controller.setAnimation('walk', atlas: atlas);

// Read state
controller.isPlaying;    // bool
controller.currentFrame; // int
controller.totalFrames;  // int
controller.animationName; // String?

// Don't forget to dispose when using externally
controller.dispose();

Precaching

Pre-cache spritesheet images to eliminate loading flash:

// Single image
await SpriteAnimation.precache(
  const AssetImage('assets/explosion.png'),
  context,
);

// Multiple images in parallel
await SpriteAnimation.precacheAll([
  const AssetImage('assets/idle.png'),
  const AssetImage('assets/walk.png'),
  const AssetImage('assets/attack.png'),
], context);

Callbacks

SpriteAnimation.grid(
  image: AssetImage('assets/explosion.png'),
  columns: 8,
  rows: 4,
  loop: false,
  onFrame: (frame) => print('Frame: $frame'),
  onComplete: () => print('Animation finished'),
)

Atlas JSON Formats

TexturePacker (hash):

{
  "frames": {
    "idle_0.png": {
      "frame": { "x": 0, "y": 0, "w": 64, "h": 64 },
      "rotated": false,
      "trimmed": false,
      "spriteSourceSize": { "x": 0, "y": 0, "w": 64, "h": 64 },
      "sourceSize": { "w": 64, "h": 64 }
    }
  },
  "meta": {
    "size": { "w": 256, "h": 256 },
    "frameTags": [
      { "name": "idle", "from": 0, "to": 3 },
      { "name": "walk", "from": 4, "to": 9 }
    ]
  }
}

Aseprite (array):

{
  "frames": [
    {
      "filename": "idle_0.png",
      "frame": { "x": 0, "y": 0, "w": 64, "h": 64 },
      "duration": 100
    }
  ],
  "meta": {
    "frameTags": [
      { "name": "idle", "from": 0, "to": 3 }
    ]
  }
}

Both formats are auto-detected.

Performance

Optimized for smooth 60fps animation rendering:

• Zero widget rebuilds: Uses CustomPainter(repaint: controller) — frame changes repaint only the paint layer, skipping build() entirely
• Zero-allocation tick loop: Raw microsecond arithmetic instead of Duration objects in the hot path
• Pre-computed frame rects: Grid source rectangles are calculated once at load time, not during paint
• Reusable Paint object: Single Paint instance reused across frames, avoiding per-frame allocations
• Accumulator-based timing: Frame advancement uses a time accumulator for accurate frame pacing
• Image precaching: precache() / precacheAll() to eliminate loading flash
• Multiple instances: Each widget runs independently with its own controller, ticker, and paint layer
• No external dependencies: Zero overhead from third-party packages

API Reference

SpriteAnimation

Property	Type	Default	Description
image	ImageProvider	required	Spritesheet image
columns	int	-	Grid columns (grid mode)
rows	int	-	Grid rows (grid mode)
frameCount	int?	columns*rows	Total frames (grid mode)
atlas	SpriteAtlas	-	Atlas data (atlas mode)
animation	String?	first	Animation name (atlas mode)
fps	double	12	Frames per second
autoPlay	bool	true	Start automatically
loop	bool	true	Loop animation
mode	PlayMode	forward	Playback direction
blendMode	BlendMode	srcOver	Canvas blend mode
fit	BoxFit	contain	How sprite fits in bounds
width	double?	-	Fixed width
height	double?	-	Fixed height
controller	SpriteAnimationController?	-	External controller
onFrame	ValueChanged<int>?	-	Frame change callback
onComplete	VoidCallback?	-	Completion callback

SpriteAnimationController

Method	Description
play()	Start or resume playback
pause()	Pause at current frame
stop()	Stop and reset to frame 0
goToFrame(int)	Jump to specific frame
setAnimation(String, {SpriteAtlas})	Switch named animation
dispose()	Clean up resources

Property	Type	Default	Description
speed	double	1	Playback multiplier applied to the whole clock
repeatCount	int?	null	Cycles to play before completing; null is unlimited
completedCycles	int	0	Cycles finished since playback started
onCycle	ValueChanged<int>?	-	Fires on every wrap of a looping animation

Speed

fps sets the base frame rate, but atlas animations carry per-frame durations and ignore it. speed scales the clock either way:

final controller = SpriteAnimationController(speed: 2);   // twice as fast
controller.speed = 0.5;                                    // half speed

Fixed repeats

// Play the effect three times, then stop and call onComplete
final controller = SpriteAnimationController(repeatCount: 3)
  ..onCycle = (done) => debugPrint('cycle $done')
  ..onComplete = () => debugPrint('done');

repeatCount only applies while loop is true: a non-looping animation always stops after one pass.

SpriteAtlas

Method	Description
SpriteAtlas.fromJson(String)	Parse from JSON string
SpriteAtlas.fromAsset(String)	Load from Flutter asset
getAnimation(String)	Get animation data by name
animationNames	List of available animation names

License

MIT