dotdart 0.9.0

Build-time Flutter asset compiler that generates typed, optimized widgets from SVG, Lottie, images, and GIFs for mobile, web, and desktop.

dotdart

Type-safe Flutter asset access, generated as optimized Dart code.

dotdart compiles supported SVG, Lottie, images, and GIFs into strongly named Flutter widgets such as $Icons.cross(), $Lotties.pulse(), and $Images.cataqui(). Asset mistakes fail during generation instead of becoming runtime surprises.

Lottie performance

For the 978 KB job-card carousel in this repository's example, the generated widget sustained 60.2 FPS while the lottie 3.5.1 player sustained 27.2 FPS:

Renderer	Frames in 10 seconds	Average UI time	Average raster time	Missed UI frames
dotdart output	602	0.434 ms	4.62 ms	0/602
lottie 3.5.1	272	32.04 ms	3.33 ms	271/272

That is about 74 times less UI-thread work and 7 times less combined UI and raster time for this animation. The comparison used the same canvas and asset for two 10-second profile-mode runs on the same macOS host. It demonstrates the relative rendering cost of these implementations, not guaranteed frame rates on every device; profile representative animations on target hardware before shipping performance-critical experiences.

Platform support

Generated widgets support Flutter on Android, iOS, Web, macOS, Windows, and Linux, including Web's JavaScript and Wasm compilation targets.

dotdart itself runs on the development machine through build_runner. Keep it in dev_dependencies; applications import the generated libraries rather than dotdart at runtime.

Why dotdart?

• Typed access: rename or remove an asset and Dart analysis finds every stale call site.
• No SVG or Lottie runtime renderer: supported vectors and animations become ordinary CustomPainter code.
• Low-resource image defaults: generated image and GIF widgets include decode sizing, intrinsic metadata, a build-time-decoded thumbhash placeholder, and per-asset cache controls.
• Build-time validation: malformed configuration, unsupported content, duplicate inputs, naming collisions, and unsafe output paths fail early.
• Self-contained output: generated libraries depend on Flutter, not dotdart.

Install

Add dotdart and build_runner as development dependencies:

flutter pub add --dev dotdart build_runner

Quick start

Configure the inputs and output in your package's pubspec.yaml:

dotdart:
  output: lib/gen/
  svg:
    - assets/icons/
  lottie:
    - assets/lotties/
  image:
    - assets/images/

flutter:
  assets:
    - assets/images/

Images and GIFs remain Flutter assets because their generated widgets use Image.asset. SVG and Lottie inputs are compiled into Dart and do not need to be listed under flutter.assets.

Generate the libraries:

dart run build_runner build

Import and use the namespace generated from each source folder:

import 'package:my_app/gen/icons.g.dart';
import 'package:my_app/gen/images.g.dart';
import 'package:my_app/gen/lotties.g.dart';
import 'package:flutter/material.dart';

final closeIcon = $Icons.close(width: 24);
final pulse = $Lotties.pulse(
  width: 96,
  delay: const Duration(milliseconds: 300),
  duration: const Duration(seconds: 2),
  playback: LottiePlayback.loop,
);
final jobCards = $Lotties.jobCards(
  width: 320,
  clip: false,
  overrides: const JobCardsOverrides(
    jobTitleText: 'Event server',
    payTextColor: Colors.green,
  ),
);
final image = $Images.profile(width: 160);

await $ImagesCache.precacheProfile(context, width: 160);
// Render $Images.profile(width: 160), then release that decoded entry later.
final removed = await $ImagesCache.removeProfile(context, width: 160);

Cache dimensions are logical pixels. Use the same width and height when precaching, rendering, and removing an image or GIF. When both dimensions are omitted, the cache methods use the generated widget's default display size. Removal preserves an image that is still being displayed while releasing its reusable cache entry.

Supported Lottie text and colors become fields on the generated overrides object. Repeated names receive numbered suffixes, such as jobTitleText2, so each layer remains independent. Unnamed layers use predictable text1, color1, and later fallbacks.

Generated Lotties clip painting to their source canvas by default. Pass clip: false when artwork should remain visible outside that boundary.

Use delay to wait once before automatic playback starts. Use duration to override the total playback time and make the animation faster or slower while preserving the relative timing of its keyframes. When duration is omitted, the animation uses the duration stored in the Lottie file.

Generated Lotties play once by default and keep their final frame visible. Pass playback: LottiePlayback.loop to repeat an animation continuously. The generated namespace library re-exports LottiePlayback, so no additional import is needed.

Supported trim paths preserve animated start, end, and offset values in the default drawing direction, including parallel and sequential handling when one shape group contains multiple paths.

Generated output

Input	Generated API	Runtime implementation
assets/icons/close.svg	$Icons.close(...)	Dependency-free CustomPainter
assets/lotties/pulse.json	$Lotties.pulse(...)	Lifecycle-aware CustomPainter
assets/images/profile.webp	$Images.profile(...)	Optimized Image.asset

Namespaces containing images or GIFs also generate a companion cache class, such as $ImagesCache. Mixed folders generate cache methods only for their image and GIF assets.

Assets are grouped by their parent folder. Mixed asset types in assets/status/ share one lib/gen/status.g.dart library and one $Status namespace.

Generated widget classes are private. Consume assets through their public namespace methods and do not edit generated files by hand.

When the package contains Lottie inputs, dotdart also writes dotdart.g.dart beside the namespace libraries for shared generated types such as LottiePlayback.

Documentation

• Configuration reference
• Supported SVG, Lottie, image, and GIF features
• Performance model
• Troubleshooting
• Runnable example

Requirements

• Dart >=3.12.0 <4.0.0
• Flutter 3.44.0 for development in this repository
• build_runner >=2.15.0 for the post-process builder flow

Status

dotdart is pre-1.0. Breaking changes can occur in minor releases and will be documented with migration guidance in the changelog.