commit 27428b3e2190e966d85e36774e499a6648394a10
parent c39ff56bebedaa274ffee3e7237a470701a77a91
Author: Jack Mordaunt <jackmordaunt.dev@gmail.com>
Date: Sun, 20 Sep 2026 15:31:26 -0300
README: update for libwebp 1.6.0 and the ccgo v4 toolchain
The toolchain section still described the v3 pipeline and its osxcross
requirement, which no longer exists.
Diffstat:
| M | README.md | | | 52 | ++++++++++++++++++++++++++++++++-------------------- |
1 file changed, 32 insertions(+), 20 deletions(-)
diff --git a/README.md b/README.md
@@ -53,26 +53,26 @@ Lower is better.
| operation | dynamic | wasm | transpiled |
| --------------------- | ------- | ---- | ---------- |
-| encode lossless | 1.0x | 2.6x | 2.5x |
-| encode lossy (q=0.75) | 1.0x | 2.7x | 4.2x |
-| decode | 1.0x | 2.3x | 4.5x |
+| encode lossless | 1.0x | 2.6x | 2.8x |
+| encode lossy (q=0.75) | 1.0x | 2.6x | 4.3x |
+| decode | 1.0x | 2.2x | 4.5x |
Megapixels per second, 1280x720 photographic:
| operation | dynamic | wasm | transpiled |
| --------------------- | ------- | ---- | ---------- |
-| encode lossless | 4.0 | 1.9 | 2.1 |
-| encode lossy (q=0.75) | 26.2 | 9.9 | 5.8 |
-| decode | 328 | 139 | 68 |
+| encode lossless | 4.0 | 1.7 | 1.7 |
+| encode lossy (q=0.75) | 25.7 | 10.0 | 5.1 |
+| decode | 309 | 133 | 56 |
Same source, six builds. SIMD accounts for the whole wasm/transpiled difference, and
lossless barely uses it:
| operation | native SIMD | native scalar | wasm zig | wasm em | wasm em+SIMD | transpiled |
| --------------- | ----------- | ------------- | -------- | ------- | ------------ | ---------- |
-| encode lossless | 1.0x | 1.2x | 3.2x | 3.2x | 2.6x | 2.5x |
-| encode lossy | 1.0x | 2.3x | 4.9x | 4.7x | 2.7x | 4.2x |
-| decode | 1.0x | 2.3x | 5.3x | 5.2x | 2.3x | 4.5x |
+| encode lossless | 1.0x | 1.2x | 3.2x | 3.2x | 2.6x | 2.8x |
+| encode lossy | 1.0x | 2.3x | 4.8x | 4.7x | 2.6x | 4.3x |
+| decode | 1.0x | 2.1x | 4.8x | 4.7x | 2.2x | 4.5x |
All backends encode byte-identically; the harness checks that before measuring.
@@ -122,17 +122,29 @@ Run `tools/test-matrix.sh` to build and test every supported tag combination.
## Toolchain
-The transpilation process relies on a cross compile toolchain.
-
-This is not strictly required at the moment, since the transpiled code is
-identical between operating systems and architectures (amd64, arm64).
-
-`tools/transpile.sh` expects these compilers on an amd64 Linux box:
-
-- gcc (gcc native)
-- aarch64-linux-gnu (gcc)
-- x86_64-w64-mingw32 (mingw)
-- x86_64-apple-darwin15 (osxcross)
+`tools/transpile.sh` regenerates `lib/transpiled` with
+[`ccgo`](https://pkg.go.dev/modernc.org/ccgo/v4) v4, one file per GOOS/GOARCH, on an
+amd64 Linux box. It needs:
+
+| tool | for |
+| ------------------------ | ------------------------------------------- |
+| `ccgo` v4 | the transpiler |
+| `zig` | darwin headers |
+| `x86_64-w64-mingw32-gcc` | windows headers |
+| `aarch64-linux-gnu-gcc` | linux/arm64 headers |
+
+ccgo v4 supplies target predefines through `--goos`/`--goarch` but not target libc
+headers, so each cross target needs a header source. zig covers darwin from its bundled
+`any-macos-any` headers, which is why no macOS SDK or osxcross install is required. It
+does not cover linux: ccgo cannot parse zig's `generic-glibc` `bits/types.h`, so
+linux/arm64 uses a real cross compiler and linux/amd64 uses the host.
+
+Two patches are applied during transpilation. libwebp declares `GetCoeffs` as a
+`volatile` function pointer, which ccgo cannot emit a call through; threading is
+disabled here so dropping `volatile` is safe. And `tools/sharpyuv_stub.c` replaces the
+sharpyuv library, whose `sharpyuv_gamma.c` is libwebp's only caller of `expf`/`logf` —
+`modernc.org/libc` provides those for linux only. Nothing reaches sharpyuv unless
+`WebPConfig.use_sharp_yuv` is set, which this package never does.
## Dynamic
