Enable building as a WASM object with emscripten.

Only tested with, and includes some specifics for, the emscripten toolchain.

CMakeLists.txt

@@ -104,6 +104,20 @@ option(WITH_HWLOC "Build sources that require libhwloc" ON)
 option(WITH_MPI "Build sources that require MPI" ON)
 # Build sources that require PCSC
 option(WITH_PCSC "Build sources that require PCSC" ON)
+# Disable things that aren't well supported under WASM
+option(BUILD_FOR_WASM "Build in a way that supports WASM" OFF)
+# Auto-enable WASM build if we can detect emscripten
+if (BUILD_FOR_WASM)
+	message(STATUS "Disabling unsupported components to enable WASM build")
+elseif(EMSCRIPTEN)
+	message(STATUS "Emscripten detected, enabling WASM by disabling unsupported components")
+	set(BUILD_FOR_WASM ON)
+endif(BUILD_FOR_WASM)
+# Use WASM exceptions (over JavaScript exceptions)
+cmake_dependent_option(WASM_EXCEPTIONS "Use WASM exceptions (instead of JavaScript exceptions)" ON "BUILD_FOR_WASM;EMSCRIPTEN" OFF)
+if (WASM_EXCEPTIONS)
+	message(STATUS "Enabling WebAssembly exception handling")
+endif (WASM_EXCEPTIONS)
 
 # Build sources that require FFMPEG. FFMPEG has *many* dynamic dependencies that
 # aren't built static on all systems, therefore we cannot guarantee they'll be

README.md

@@ -200,16 +200,22 @@ Options
 The CMake build supports the following options:
 
 | CMake Option            | Default | Description                                          | Notes |
-|:-----------------------:|:-------:|:----------------------------------------------------:|:-----:|
+|:------------------------|:-------:|:-----------------------------------------------------|:------|
 | `BUILD_BIOMEVAL_32BIT`  | `OFF`   | Compile 32-bit on 64-bit host OS                     ||
 | `BUILD_BIOMEVAL_TESTS`  | `OFF`   | Build test programs                                  ||
+| `BUILD_FOR_WASM` | `OFF` | Disable components currently not supported under WebAssembly | Defaults to `ON` when the [Emscripten](https://emscripten.org) toolchain is detected |
 | `BUILD_SHARED_LIBS`     | `OFF`    | Build shared library (i.e., `.so`, `.dll`, `.dylib`) | When `OFF`, a static library (i.e., `.a`, `.lib`) is built instead |
 | `FORCE_STATIC_DEPENDENCIES` | `OFF` | Force linking against `.a`/`.lib` third-party dependencies. | Unavailable on Windows (use `-DBUILD_SHARED_LIBS=OFF` for similar behavior) |
+| `WASM_EXCEPTIONS` | `ON` | When compiled to WebAssembly, use WebAssembly exceptions instead of JavaScript exceptions | Only available when `BUILD_FOR_WASM` is `YES` and the [Emscripten](https://emscripten.org) toolchain is detected |
 | `WITH_FFMPEG` | `ON` | Build sources that require [FFMPEG](https://ffmpeg.org) | Unavailable when `FORCE_STATIC_DEPENDENCIES` is `ON` |
 | `WITH_HWLOC` | `ON` | Build sources that require [libhwloc](https://www.open-mpi.org/projects/hwloc/) |
 | `WITH_MPI` | `ON` | Build sources that require [OpenMPI](https://www.open-mpi.org/) |
 | `WITH_PCSC` | `ON` | Build sources that require [PCSC](https://pcsclite.apdu.fr) |
 
+### A Note about WebAssembly
+
+A minimal version of the library can be compiled to WebAssembly and is supported. Compilation has only been tested using the [Emscripten](https://emscripten.org) toolchain. When this toolchain is detected (i.e., when `emcmake` is used to configure, rather than `cmake`), the above options for WebAssembly are automatically enabled.
+
 ---
 
 As Seen In...

src/libbiomeval/CMakeLists.txt

@@ -40,6 +40,23 @@
 
 cmake_minimum_required(VERSION 2.8.11)
 
+if (BUILD_FOR_WASM)
+	add_definitions("-DWASM")
+	if (EMSCRIPTEN)
+		set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -sUSE_LIBPNG=1 -sUSE_LIBJPEG=1")
+		set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -sUSE_LIBPNG=1 -sUSE_LIBJPEG=1")
+
+		if (WASM_EXCEPTIONS)
+			set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -sSUPPORT_LONGJMP=wasm")
+			set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fwasm-exceptions")
+			set(LDFLAGS "${LDFLAGS} -fwasm-exceptions")
+			set(PNG_NAMES "png-wasm-sjlj")
+		endif (WASM_EXCEPTIONS)
+	endif (EMSCRIPTEN)
+
+	set(WITH_HWLOC OFF)
+endif()
+
 if (${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" AND FORCE_STATIC_DEPENDENCIES)
 	# No static libhwloc in MacPorts
 	set(WITH_HWLOC OFF)
@@ -193,6 +210,16 @@ endif(MSVC)
 #	VIDEO if the required libraries are present.
 #
 set(PACKAGES ${CORE} ${IO} ${RECORDSTORE} ${IMAGE} ${FEATURE} ${VIEW} ${DATA} ${FINGER} ${PALM} ${PLANTAR} ${IRIS} ${FACE} ${PROCESS} ${MESSAGE_CENTER})
+if (BUILD_FOR_WASM)
+	# We're not concerned with these packages for WebAssembly
+	list(REMOVE_ITEM PACKAGES ${PROCESS} ${MESSAGE_CENTER})
+
+	# XXX: Remove RecordStore support simply to reduce the number of
+	#      dependencies that need to be recompiled for the WASM
+	#      architecture. It is likely they can be added back in the future.
+	list(REMOVE_ITEM PACKAGES ${RECORDSTORE})
+endif (BUILD_FOR_WASM)
+
 
 if (WITH_FFMPEG)
   # Our FindFFMPEG.cmake is not sufficient for finding all of FFMPEG's
@@ -412,13 +439,17 @@ endif (MSVC)
 # For OS-X, add paths where the ports packages are placed.
 #
 if(CMAKE_HOST_APPLE)
+  if (NOT BUILD_FOR_WASM)
   target_include_directories(coreobjs PUBLIC /opt/local/include)
   set_target_properties(${CORELIB} PROPERTIES MACOSX_RPATH ON)
   target_link_libraries(${CORELIB} -L/opt/local/lib)
+  endif (NOT BUILD_FOR_WASM)
   if (PCSC_FOUND)
 	target_link_libraries(${CORELIB} ${PCSC_FRAMEWORK})
   endif (PCSC_FOUND)
+  if (NOT BUILD_FOR_WASM)
   add_definitions("-DDarwin")
+  endif(NOT BUILD_FOR_WASM)
 endif(CMAKE_HOST_APPLE)
 
 target_include_directories(coreobjs PUBLIC ${BIOMEVAL_INCLUDE} ${NBIS_INCLUDE})
@@ -460,13 +491,15 @@ endif (${CMAKE_SYSTEM_NAME} STREQUAL "Darwin" AND BLOCK_SUPPORT)
 #
 # Berkeley DB
 #
+if (NOT BUILD_FOR_WASM)
 set(BERKELEYDB_FIND_REQUIRED TRUE)
 find_package(BERKELEYDB)
 if(NOT BERKELEYDB_FOUND)
   message(FATAL_ERROR "Could not find Berkeley Database.")
 endif(NOT BERKELEYDB_FOUND)
 include_directories(PUBLIC ${BERKELEYDB_INCLUDE_DIR})
 target_link_libraries(${CORELIB} ${BERKELEYDB_LIBRARIES})
+endif()
 
 #
 # OpenJPEG and JPEG2000
@@ -530,9 +563,11 @@ endif (WITH_HWLOC)
 target_link_libraries(${CORELIB}
     $<$<AND:$<CXX_COMPILER_ID:GNU>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,9.0>>:stdc++fs>)
 
+if (NOT BUILD_FOR_WASM)
 # This will use our Module
 find_package(SQLITE3 REQUIRED)
 target_link_libraries(${CORELIB} ${SQLITE3_LIBRARIES})
+endif()
 
 # libtiff, like ffmpeg, writes a pkg-config, but it prefers to link against
 # shared libs. We can't have that with this option.