You can configure your project to automatically transform assets at build time using compatible Dart packages.

In thepubspec.yaml file, list the assets to be transformed and the associated transformer package.

flutter:assets:-path:assets/logo.svgtransformers:-package:vector_graphics_compiler

With this configuration,assets/logo.svg is transformed by thevector_graphics_compiler package as it is copied to the build output. This package precompiles SVG files into an optimized binary files that can be displayed using thevector_graphics package, like so:

import'package:vector_graphics/vector_graphics.dart';​constWidgetlogo=VectorGraphic(loader:AssetBytesLoader('assets/logo.svg'));

To pass a string of arguments to an asset transformer, also specify that in the pubspec:

flutter:assets:-path:assets/logo.svgtransformers:-package:vector_graphics_compilerargs:['--tessellate','--font-size=14']

Asset transformers can be chained and are applied in the order they are declared. Consider the following example using imaginary packages:

flutter:assets:-path:assets/bird.pngtransformers:-package:grayscale_filter-package:png_optimizer

Here,bird.png is transformed by thegrayscale_filter package. The output is then transformed by thepng_optimizer package before being bundled into the built app.

An asset transformer is a Dartcommand-line app that is invoked withdart run with at least two arguments:--input, which contains the path to the file to transform and--output, which is the location where the transformer code must write its output to.

If the transformer finishes with a non-zero exit code, the application build fails with error message explaining that transformation of the asset failed. Anything written to thestderr stream of the process by the transformer is included in the error message.

During the invocation of the transformer, theFLUTTER_BUILD_MODE environment variable will be set to the CLI name of the build mode being used. For example, if you run your app withflutter run -d macos --release, thenFLUTTER_BUILD_MODE will be set torelease.

For a sample Flutter project that uses asset transformation and includes a custom Dart package that is used as a transformer, check out theasset_transformers project in the Flutter samples repo.