MetaCrate/crates/libremetaverse-imaging-skia/README.md

MetaCrate Skia adapter

This crate implements the pinned SkiaTextureCodec behavior at a bounded, project-owned image boundary. The core libremetaverse-imaging crate never exposes a skia-safe type and never discovers or links Skia.

Features and formats

The default feature set has no Skia dependency. SkiaTextureCodec::decode returns a typed InvalidOperation error in that configuration, while conversion from the checked project-owned backend::SKBitmap remains available for tests and callers that already own decoded pixels.

Enable native decoding with:

cargo test -p libremetaverse-imaging-skia --features skia

The skia feature decodes the CPU codec formats supported by the pinned rust-skia release: BMP, GIF, ICO, JPEG, PNG, WBMP, and WebP. Input is buffered to at most 64 MiB. Dimensions are rejected before native pixel allocation when they exceed the core 16,777,216-pixel limit, and decoded storage uses checked strides and owned Rust buffers.

The mapped C# adapter exposes decoding and SKBitmap-to-ManagedImage conversion only; it has no encoding or resize method. Encoding selection stays with the format-specific imaging APIs, and callers use ManagedImage's checked resize methods after decoding. Premultiplied pixels are converted to straight alpha at this boundary. RGB565, BGRA8888, RGBA8888, RGBA/BGRA1010102, Gray8, Alpha8, row padding, and the reference byte-width fallback retain the pinned C# channel and rounding rules.

Binary cache and source builds

skia-safe 0.99.0 downloads an official prebuilt Skia archive when the target and Cargo feature set match a published archive. MetaCrate deliberately selects the published WebP-capable feature sets:

• Linux and Windows: JPEG, PDF, SVG, text layout, Vulkan, and WebP;
• macOS: JPEG, PDF, SVG, text layout, and WebP.

Vulkan is selected on Linux and Windows only to match the published CPU/WebP archive; this adapter does not create a GPU context or call a platform graphics API. The same feature is therefore usable on macOS, Linux, and Windows without leaking platform-specific behavior.

Build prerequisites for the supported desktop targets are:

• Linux: a C++ linker/runtime, curl, pkg-config, FreeType, and Fontconfig;
• macOS: Xcode command-line tools and curl;
• Windows MSVC: the Rust MSVC toolchain, Visual Studio C++ build tools, and curl.

The build script downloads cache archives from the rust-skia/skia-binaries GitHub releases. Pin or mirror SKIA_BINARIES_URL in offline/reproducible build environments. FORCE_SKIA_BINARIES_DOWNLOAD=1 makes a missing archive fail instead of compiling Skia. If no archive matches and that variable is absent, rust-skia falls back to a source build, which additionally requires Python 3, Ninja, and an LLVM/Clang toolchain. FORCE_SKIA_BUILD=1 selects that path explicitly.

Licensing and redistribution

skia-safe and rust-skia's bindings are MIT licensed; the linked Skia library is BSD-3-Clause licensed. Official binary-cache archives contain compiled Skia. Products that redistribute the resulting native artifacts must preserve the applicable MIT and BSD notices and audit the exact archive they ship.