Summary of Changes

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This pull request introduces the capability to build COLMAP as shared libraries, offering an alternative to the default static library build. This change primarily benefits development workflows by potentially speeding up edit-compile-test cycles due to faster incremental linking. The build system has been updated to support this new option, and comprehensive documentation has been added to guide users on its usage and implications.

Highlights

• Shared Library Build Option: A new CMake option, BUILD_SHARED_LIBS, has been introduced to allow users to build COLMAP as shared libraries instead of the default static libraries. This option is set to OFF by default.
• CMake Macro Refinement: The COLMAP_ADD_LIBRARY macro in CMakeHelper.cmake has been updated to dynamically determine the library type (static or shared) based on the BUILD_SHARED_LIBS option, removing the previous hardcoded default to STATIC.
• Documentation Update: The doc/install.rst file now includes a dedicated section on building shared libraries, outlining the command to enable the option and discussing the trade-offs between shared and static libraries (e.g., faster incremental linking vs. runtime performance).
• GTest/GMock Linking for Shared Libraries: Special handling has been added to src/colmap/util/CMakeLists.txt to correctly link gtest and gmock when building shared libraries. This involves platform-specific linker flags (-Wl,--whole-archive, /WHOLEARCHIVE, -Wl,-force_load) to ensure all symbols are available and avoid duplicate singletons.
• Library Dependency Adjustments: Several CMakeLists.txt files (src/colmap/retrieval, src/colmap/sensor, src/colmap/ui) have had their PUBLIC_LINK_LIBS and PRIVATE_LINK_LIBS adjusted to correctly propagate dependencies, especially in the context of shared library builds.

Changelog

• CMakeLists.txt
  • Added BUILD_SHARED_LIBS CMake option, defaulting to OFF.
• cmake/CMakeHelper.cmake
  • Removed explicit default to STATIC for COLMAP_ADD_LIBRARY_TYPE.
  • Modified add_library call to no longer explicitly specify STATIC type.
  • Removed the FATAL_ERROR for unknown library types.
• doc/install.rst
  • Added a new section titled 'Shared Libraries' to the installation documentation.
  • Included instructions for enabling BUILD_SHARED_LIBS.
  • Provided a detailed comparison of trade-offs between static and shared libraries.
• src/colmap/retrieval/CMakeLists.txt
  • Moved colmap_util, colmap_math, and colmap_feature_types from PRIVATE_LINK_LIBS to PUBLIC_LINK_LIBS.
• src/colmap/sensor/CMakeLists.txt
  • Moved colmap_geometry and colmap_util from PRIVATE_LINK_LIBS to PUBLIC_LINK_LIBS.
• src/colmap/ui/CMakeLists.txt
  • Added colmap_mvs to PUBLIC_LINK_LIBS.
• src/colmap/util/CMakeLists.txt
  • Relocated target_sources for testing files to be conditional on TESTS_ENABLED.
  • Implemented conditional linking logic for gtest/gmock based on BUILD_SHARED_LIBS for colmap_util, using platform-specific whole-archive flags.
  • Adjusted colmap_gtest_main linking to include colmap_util publicly and conditionally link GTest::gmock_main for static builds.

Activity

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