Chili Palmer
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69 lines
3.1 KiB
Markdown
69 lines
3.1 KiB
Markdown
# MetaCrate Skia adapter
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This crate implements the pinned `SkiaTextureCodec` behavior at a bounded,
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project-owned image boundary. The core `libremetaverse-imaging` crate never
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exposes a `skia-safe` type and never discovers or links Skia.
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## Features and formats
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The default feature set has no Skia dependency. `SkiaTextureCodec::decode`
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returns a typed `InvalidOperation` error in that configuration, while conversion
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from the checked project-owned `backend::SKBitmap` remains available for tests
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and callers that already own decoded pixels.
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Enable native decoding with:
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```sh
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cargo test -p libremetaverse-imaging-skia --features skia
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```
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The `skia` feature decodes the CPU codec formats supported by the pinned
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rust-skia release: BMP, GIF, ICO, JPEG, PNG, WBMP, and WebP. Input is buffered
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to at most 64 MiB. Dimensions are rejected before native pixel allocation when
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they exceed the core 16,777,216-pixel limit, and decoded storage uses checked
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strides and owned Rust buffers.
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The mapped C# adapter exposes decoding and `SKBitmap`-to-`ManagedImage`
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conversion only; it has no encoding or resize method. Encoding selection stays
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with the format-specific imaging APIs, and callers use `ManagedImage`'s checked
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resize methods after decoding. Premultiplied pixels are converted to straight
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alpha at this boundary. RGB565, BGRA8888, RGBA8888, RGBA/BGRA1010102, Gray8,
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Alpha8, row padding, and the reference byte-width fallback retain the pinned
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C# channel and rounding rules.
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## Binary cache and source builds
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`skia-safe` 0.99.0 downloads an official prebuilt Skia archive when the target
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and Cargo feature set match a published archive. MetaCrate deliberately selects
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the published WebP-capable feature sets:
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- Linux and Windows: JPEG, PDF, SVG, text layout, Vulkan, and WebP;
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- macOS: JPEG, PDF, SVG, text layout, and WebP.
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Vulkan is selected on Linux and Windows only to match the published CPU/WebP
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archive; this adapter does not create a GPU context or call a platform graphics
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API. The same feature is therefore usable on macOS, Linux, and Windows without
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leaking platform-specific behavior.
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Build prerequisites for the supported desktop targets are:
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- Linux: a C++ linker/runtime, `curl`, `pkg-config`, FreeType, and Fontconfig;
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- macOS: Xcode command-line tools and `curl`;
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- Windows MSVC: the Rust MSVC toolchain, Visual Studio C++ build tools, and
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`curl`.
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The build script downloads cache archives from the `rust-skia/skia-binaries`
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GitHub releases. Pin or mirror `SKIA_BINARIES_URL` in offline/reproducible build
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environments. `FORCE_SKIA_BINARIES_DOWNLOAD=1` makes a missing archive fail
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instead of compiling Skia. If no archive matches and that variable is absent,
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rust-skia falls back to a source build, which additionally requires Python 3,
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Ninja, and an LLVM/Clang toolchain. `FORCE_SKIA_BUILD=1` selects that path
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explicitly.
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## Licensing and redistribution
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`skia-safe` and rust-skia's bindings are MIT licensed; the linked Skia library
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is BSD-3-Clause licensed. Official binary-cache archives contain compiled Skia.
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Products that redistribute the resulting native artifacts must preserve the
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applicable MIT and BSD notices and audit the exact archive they ship.
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