assets-for-api-docs

This repo is used to host and serve static assets in support of docs.flutter.dev, as well as some manual tests that use specially-crafted graphics.

Assets committed to this repo and pushed to GitHub are immediately available for linking and reference.

Adding new assets

In accordance with the Flutter style guide, assets submitted to this repository should be easily reproducible, e.g. by running a Flutter app or a script. This makes it easier to update the asset in the future, if needed. Check the existing diagrams (and their generation code) in this repository to see examples. Avoid checking in just a static image file (e.g. PNG, JPEG), without a way to regenerate and update it.

Creating new diagrams

To create a new diagram:

  1. Create a new Dart file inside /packages/diagrams/lib/src/.

  2. Export that file from /packages/diagrams/lib/diagrams.dart.

  3. Create one or more diagram widgets that mix-in DiagramMetadata, overriding the name getter to return their name, which should be lower_snake_case.

    • If your diagram is animated, override the duration getter to return the duration of the animation.

    • If your diagram’s state needs to wait imperatively, mix-in LockstepStateMixin and call waitLockstep(duration).

    • If your diagram needs simulated gesture input, acquire a WidgetController by calling DiagramWidgetController.of(context).

  4. Create a class that extends DiagramStep.

  5. Override the diagrams getter of DiagramStep to return a list containing the new diagrams.

  6. Override the category getter of DiagramStep to return the category it belongs in, this corresponds to the folders under /assets.

  7. Add your new DiagramStep to the list in packages/diagrams/lib/src/steps.dart, sorted alphabetically.

  8. Generate assets with bin/generate -s MyDiagramStep, for more options see the generation section.

URL structure

Reference the assets with this URL structure:

https://flutter.github.io/assets-for-api-docs/assets/<library>/<asset>

For example, an image named app_bar.png about AppBar from the material library would go in the assets/material/ directory and be at https://flutter.github.io/assets-for-api-docs/assets/material/app_bar.png.

All asset files should be under the assets directory in an appropriate subdirectory.

Generation

Images must be code-generated.

To create new images, see the packages/diagrams/lib/src/ directory.

The generate.dart script regenerates almost all of existing assets using the Flutter version you have installed. A small wrapper bin/generate (bin\generate.bat on Windows) is provided as a convenience.

To limit image generation to certain categories and/or names, run:

# Filter by category
bin/generate -c cupertino,material
# Filter by name
bin/generate -n basic_material_app,blend_mode
# Filter by step class name
bin/generate -s MaterialAppDiagramStep,BlendModeDiagramStep

bin/generate --help lists available arguments.

Prerequisites

The generate.dart script works on macOS, Linux, and Windows, but it needs several prerequisites in order to run. On Linux and macOS run bin/generate. On Windows, run bin\generate.bat.

To optimize PNG files, it needs optipng, which is available for macOS via Homebrew, and Linux via apt-get, and Windows from the optipng website.

To convert animations into mp4 files, it needs ffmpeg, available for macOS via Homebrew and Linux via apt-get, and for Windows from the FFMPEG website.

Both optipng and ffmpeg need to be in your path when you run the generate script.

The commands flutter, dart, and (when using an Android device) adb need to be available in a directory in the PATH environment variable (e.g. PATH=~/<path_to_flutter>/flutter/bin/cache/dart-sdk/bin:~/Android/Sdk/platform-tools:$PATH). The script needs the most recent development version of Flutter and is not intended to work with released Flutter versions.

When using an Android device, be sure that the adb command is the same as the one running as a server (which is often started by your IDE, so use the same adb the IDE is running).

You cannot currently generate docs on an iOS device (although you can generate them on macOS).

Optimization

Please consider optimization tools for assets.

For PNGs, we recommend optipng, using the following command line:

optipng -zc1-9 -zm1-9 -zs0-3 -f0-5 *.png

Be careful about applying this aggressively. In particular, files in the assets/tests directory should not be optimized.

The automatic generation tool will automatically apply optimization to the assets it generates.

Issues

Please file any issues in the main flutter repo.

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