| name | lastfm-widget-webp-cgo |
| description | CGO and libwebp guidance for the vendored WebP animation encoder, static Linux builds, musl toolchain, encoder settings, and Docker/GoReleaser release paths. |
Lastfm Widget Webp CGO
Use this skill when changing pkg/webpanimation, cgo settings, static linking,
Docker build stages, GoReleaser configuration, or animated WebP encoding
parameters.
Encoder Boundary
pkg/webpanimation/ contains Go bindings plus a vendored libwebp source tree.
It is not ordinary application code. Avoid broad formatting, file moves, or
style refactors in this tree.
The application uses:
webpanimation.NewWebpAnimationWebPAnimEncoderOptions.SetKmin(9)WebPAnimEncoderOptions.SetKmax(17)webpConfig.SetLossless(1)- 200ms frame intervals
Changing these values affects output quality, size, and animation behavior.
Toolchain Rules
CGO is required. Linux release builds use:
CGO_ENABLED=1 CC=musl-gcc go build \
--ldflags '-linkmode=external -extldflags="-static"' \
-tags exec_local,save_s3
Docker and GoReleaser both rely on musl for static Linux binaries. Do not remove
CGO_ENABLED=1, CC=musl-gcc, or external static linking without replacing the
release validation path.
Docker And Release
Dockerfile stage build creates the static binary.goreleaser-local-runtime is the Docker target used by .goreleaser.yaml..github/workflows/release.yml runs GoReleaser for v* tags.
When changing release behavior, inspect all three files together.
Validation
For encoder or cgo changes, run:
go test -tags exec_local,save_s3 ./...
For release or Docker changes, add one targeted Linux build or Docker build
check. Prefer the relevant Docker target over running a full release.
Risk Checks
- Pure-Go replacements are not drop-in unless they preserve animated WebP
quality and timing requirements.
- macOS local compile success does not prove Linux static release success.
pkg/webpanimation C sources may produce noisy diffs if auto-formatters touch
them. Keep patches tight.
