Rust BMP decoder

This directory contains helpers, simplifications, and wrappers for exposing a custom Rust BMP decoder to other Skia code:

• to SkBmpRustCodec

Chromium build instructions

To build and test the code from this directory from Chromium:

1. autoninja -C out/... gfx_unittests blink_platform_unittests chrome
2. out/.../gfx_unittests --gtest_filter=*BMP*
3. out/.../blink_platform_unittests --gtest_filter=*BMP*

Skia build instructions

Bazel

To build the code from this directory from Skia:

$ cd skia-repo-root
$ bazelisk build //src/codec:rust_bmp_decoder //experimental/rust_bmp/...

To run unit tests:

$ bazelisk test //experimental/rust_bmp/ffi:test_bmp_ffi

To build the fuzzer:

$ bazelisk build //experimental/rust_bmp/ffi:fuzz_rust_bmp

To run the fuzzer with the corpus:

$ for bmp in experimental/rust_bmp/fuzz/corpus/*.bmp; do
    cat "$bmp" | bazel-bin/experimental/rust_bmp/ffi/fuzz_rust_bmp
  done

See validation_artifacts/TESTING.md for detailed test documentation and validation_artifacts/FUZZING.md for fuzzing documentation.

gn / ninja

To build the code from this directory from Skia:

1. gn args out/RustBmp and set skia_use_rust_bmp_decode = true
2. gn gen out/RustBmp
3. autoninja -C out/RustBmp dm

To test the code:

$ out/RustBmp/dm --src tests --nogpu
--match Codec_bmp

## Features

### **Complete Format Support**

- **Bit Depths**: 1-bit, 4-bit, 8-bit, 16-bit, 24-bit, 32-bit
- **Compression**: Uncompressed (BI_RGB), RLE4, RLE8, Bitfields (BI_BITFIELDS)
- **Advanced**: OS/2 bitmap variants
- **Color Spaces**: sRGB, embedded ICC profiles (when available)

### **Security & Robustness**

- **Memory Safety**: Complete overflow protection with u64 arithmetic
- **Input Validation**: Comprehensive header and stream validation
- **Corruption Detection**: Advanced detection of malformed files
- **Standards Compliance**: 100% conformance with bmptestsuite-0.9

### **Performance & Integration**

- **Zero-Copy**: Efficient memory handling with minimal allocations
- **FFI Optimized**: Clean Rust-to-C++ interface via CXX bridge
- **Conditional Build**: Integrated with Skia's build system

## Architecture

experimental/rust_bmp/ ├── ffi/ # Rust implementation core │ ├── lib.rs # Crate root │ ├── FFI.rs # C++ interface bridge │ ├── bmp_decoder.rs # Main BMP decoding logic │ ├── bmp_header.rs # BMP header parsing and validation │ ├── bmp_constants.rs # Format constants and definitions │ ├── bmp_types.rs # Type definitions │ ├── bmp_icc.rs # ICC profile support through moxcms crate │ ├── bmp_jpeg_decoder.rs # Embedded JPEG handling through zune-jpeg crate │ ├── bmp_png_decoder.rs # Embedded PNG handling through png crate │ └── BUILD.bazel # Bazel build configuration ├── decoder/ # C++ integration layer │ ├── SkBmpRustDecoder.h/.cpp # Skia SkCodec factory │ ├── impl/ │ │ └── SkBmpRustCodec.h/.cpp # Core codec implementation │ └── BUILD.bazel # Bazel build configuration └── README.md # This file

## Differences between `SkBmpCodec` and `SkBmpRustCodec`

* `SkBmpCodec`:
    - C++ implementation with manual memory management
    - Legacy codebase with accumulated technical debt
* `SkBmpRustCodec` differences:
    - Memory-safe Rust implementation
    - Comprehensive overflow protection with u64 arithmetic
    - Enhanced corruption detection for malformed files
    - Improved BMP standards compliance