fil/crates/kreuzberg-tesseract/patches/README.md

Tesseract WASM Patches

This directory contains patches needed to compile Tesseract for WebAssembly (WASM) targets using WASI SDK.

These patches are vendored from the tesseract-wasm project and have been proven to work with WASM compilation.

Patches

tesseract.diff

A comprehensive patch that makes Tesseract compatible with WASM compilation. The patch includes the following changes:

1. CMakeLists.txt Modifications

• New CMake option: BUILD_TESSERACT_BINARY (default: ON)

  • Allows disabling the Tesseract CLI binary build, which is not needed for WASM
  • Wraps all executable and installation targets for the tesseract binary

• Disabled components for WASM:

  • Removes OpenCL support (src/opencl/*.cpp) - not applicable to WASM
  • Removes viewer support (src/viewer/*.cpp) - UI components not needed for WASM
  • Removes C API bindings (src/api/capi.cpp) - only hocrrenderer is kept
  • Removes PDF and rendering support files:
    • src/api/renderer.cpp
    • src/api/altorenderer.cpp
    • src/api/lstmboxrenderer.cpp
    • src/api/pdfrenderer.cpp
    • src/api/wordstrboxrenderer.cpp

2. SIMD Detection Fixes (src/arch/simddetect.cpp)

• Guards CPUID detection with #if !defined(__wasm__)
• Prevents attempts to use CPU feature detection that don't exist in WASM
• The HAS_CPUID macro is only defined for non-WASM builds
• This allows the code to gracefully handle WASM's SIMD limitations

3. Pointer Type Fixes (src/ccmain/pageiterator.cpp, src/ccmain/pagesegmain.cpp, src/ccmain/tesseractclass.cpp)

Changed from stack allocation to heap allocation in tesseractclass.h:

• pixa_debug_ changed from DebugPixa to std::unique_ptr<DebugPixa>
• This prevents large allocations on the stack, which is limited in WASM

Updated all references throughout the codebase:

• .get() calls added where raw pointers are needed
• Arrow operator -> replaces dot operator . for member access
• Null checks added before dereferencing to prevent crashes

Affected functions:

• PageIterator::Orientation() - added null vector check
• Tesseract::AutoPageSeg() - updated pointer passing
• Tesseract::SetupPageSegAndDetectOrientation() - multiple pointer updates
• Tesseract::Clear() - added null check before WritePDF
• Tesseract::PrepareForPageseg() - updated Split() calls
• Tesseract::PrepareForTessOCR() - updated Split() calls

4. Additional Fixes

• Orientation detection: Changed comparison from > 0.0F to >= 0.0F in pageiterator.cpp to handle null vectors gracefully when orientation info is not available

How to Apply

These patches are applied during the WASM build process. They modify the Tesseract source code to:

1. Disable WASM-incompatible features (OpenCL, viewers, renderers)
2. Prevent CPUID detection in WASM environment
3. Use heap allocation instead of stack allocation for large objects
4. Handle missing pointer initialization gracefully

Source

These patches are based on the proven WASM compilation approach used by the tesseract.js project, which successfully compiles Tesseract to WebAssembly and deploys it in production environments.