feat: Make C++ exceptions and RTTI configurable (#9913)

Introduced the FILAMENT_ENABLE_EXCEPTIONS (default ON) and FILAMENT_ENABLE_RTTI (default OFF) CMake options to control these features globally. This replaces previous hardcoded, platform-specific overrides. Added a -E flag to build.sh to easily disable exceptions during build configuration. Removed hardcoded -fno-exceptions and -fno-rtti from android/build.gradle to allow CMake to control these flags, but kept -fno-rtti enabled by default for the Java/Android build as requested. Documented in CMakeLists.txt and BUILDING.md that the JNI library (Android/Java build) requires exceptions to be enabled. Enabled RTTI specifically for the assimp target in third_party/libassimp/tnt/CMakeLists.txt to fix compilation errors caused by its use of dynamic_cast. SIZEGUARD_BYPASS
2026-04-23 09:52:26 -07:00
parent fd2684513e
commit f9e56a11d1
5 changed files with 46 additions and 23 deletions
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -79,6 +79,10 @@ The following CMake options are boolean options specific to Filament:
 - `FILAMENT_INSTALL_BACKEND_TEST`: Install the backend test library so it can be consumed on iOS
 - `FILAMENT_USE_EXTERNAL_GLES3`:   Experimental: Compile Filament against OpenGL ES 3
 - `FILAMENT_SKIP_SAMPLES`:         Don't build sample apps
+- `FILAMENT_ENABLE_EXCEPTIONS`:    Enable C++ exceptions (default: ON, OFF for iOS). Required for JNI bindings.
+- `FILAMENT_ENABLE_RTTI`:          Enable C++ RTTI (default: OFF).
+
+Note: If you intend to use the JNI library (Android/Java build), you need to have `FILAMENT_ENABLE_EXCEPTIONS` enabled. If you are using Filament on Android as a pure native library and want to save space, you can disable it (e.g., using `./build.sh -E`).

 To turn an option on or off:

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -33,6 +33,20 @@ project(TNT C CXX ${EXTRA_LANGS})
 # ==================================================================================================
 option(FILAMENT_USE_EXTERNAL_GLES3 "Experimental: Compile Filament against OpenGL ES 3" OFF)

+# Note: If you intend to use the JNI library (Android/Java build), you need to have
+# exceptions enabled (the default). If you are using Filament on Android as a pure
+# native library and want to save space, you can disable them.
+# We disable exceptions on iOS by default. This fixes an availability error we see when using
+# std::visit and std::get, which are not supported on iOS 11.0 when exceptions are enabled.
+if (IOS)
+    set(FILAMENT_ENABLE_EXCEPTIONS_DEFAULT OFF)
+else()
+    set(FILAMENT_ENABLE_EXCEPTIONS_DEFAULT ON)
+endif()
+option(FILAMENT_ENABLE_EXCEPTIONS "Enable C++ exceptions" ${FILAMENT_ENABLE_EXCEPTIONS_DEFAULT})
+
+option(FILAMENT_ENABLE_RTTI "Enable C++ RTTI" OFF)
+
 option(FILAMENT_ENABLE_LTO "Enable link-time optimizations if supported by the compiler" OFF)
 option(FILAMENT_SKIP_SAMPLES "Don't build samples" OFF)

@@ -107,6 +121,15 @@ set(FILAMENT_OSMESA_PATH "" CACHE STRING
 # Enable exceptions by default in spirv-cross.
 set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS OFF)

+if (NOT FILAMENT_ENABLE_EXCEPTIONS)
+    add_compile_options(-fno-exceptions)
+    set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS ON)
+endif()
+
+if (NOT FILAMENT_ENABLE_RTTI)
+    add_compile_options(-fno-rtti)
+endif()
+
 # ==================================================================================================
 # CMake policies
 # ==================================================================================================
@@ -416,8 +439,7 @@ if (ANDROID)
 endif()

 if (CYGWIN)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-exceptions -fno-rtti")
-    set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS ON)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
 endif()

 if (MSVC)
@@ -451,30 +473,17 @@ if (NOT MSVC)
    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -ffunction-sections -fdata-sections")
 endif()

-# On Android RELEASE builds, we disable exceptions and RTTI to save some space (about 75 KiB
-# saved by -fno-exception and 10 KiB saved by -fno-rtti).
-if (ANDROID OR IOS OR WEBGL)
-    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fno-exceptions -fno-rtti")
-    set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS ON)
-
-    if (ANDROID OR WEBGL)
-        # Omitting unwind info prevents the generation of readable stack traces in crash reports on iOS
-        set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fno-unwind-tables -fno-asynchronous-unwind-tables")
-    endif()
+if (ANDROID OR WEBGL)
+    # On Android and WebGL RELEASE builds, we omit unwind info to save space.
+    # (We keep unwind info on iOS to allow readable stack traces in crash reports.)
+    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fno-unwind-tables -fno-asynchronous-unwind-tables")
 endif()

-# Turn off exceptions on iOS debug as well. This fixes an availability error we see when using
-# std::visit, which is not supported on iOS 11.0 when exceptions are enabled.
-if (IOS)
-    set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -fno-exceptions")
-    set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS ON)
-endif()
-
-# With WebGL, we disable RTTI even for debug builds because we pass emscripten::val back and forth
+# With WebGL, we disable RTTI because we pass emscripten::val back and forth
 # between C++ and JavaScript in order to efficiently access typed arrays, which are unbound.
 # NOTE: This is not documented in emscripten so we should consider a different approach.
 if (WEBGL)
-    set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -fno-rtti")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
 endif()

 if (WEBGL_PTHREADS)
--- a/android/build.gradle
+++ b/android/build.gradle
@@ -145,7 +145,6 @@ buildscript {
    ext.cppFlags = [
        "-std=c++17",
        "-fno-stack-protector",
-        "-fno-exceptions",
        "-fno-unwind-tables",
        "-fno-asynchronous-unwind-tables",
        "-fno-rtti",
--- a/build.sh
+++ b/build.sh
@@ -44,6 +44,8 @@ function print_help {
    echo "        Run all unit tests, will trigger a debug build if needed."
    echo "    -v"
    echo "        Exclude Vulkan support from the Android build."
+    echo "    -E"
+    echo "        Disable C++ exceptions."
    echo "    -W"
    echo "        Include WebGPU support for the target platform. (NOT functional atm)."
    echo "    -s"
@@ -275,6 +277,7 @@ function build_tools_for_split_build {
        -DCMAKE_BUILD_TYPE="${build_type_arg}" \
        ${WEBGPU_OPTION} \
        ${architectures} \
+        ${EXCEPTIONS_OPTION} \
        ../..

    ${BUILD_COMMAND} ${WEB_HOST_TOOLS}
@@ -318,6 +321,7 @@ function build_desktop_target {
            ${BACKEND_DEBUG_FLAG_OPTION} \
            ${STEREOSCOPIC_OPTION} \
            ${OSMESA_OPTION} \
+            ${EXCEPTIONS_OPTION} \
            ${architectures} \
            ../..
        ln -sf "out/cmake-${lc_target}/compile_commands.json" \
@@ -378,6 +382,7 @@ function build_webgl_with_target {
            -DWEBGL=1 \
            ${WEBGPU_OPTION} \
            ${BACKEND_DEBUG_FLAG_OPTION} \
+            ${EXCEPTIONS_OPTION} \
            ../..
        ln -sf "out/cmake-webgl-${lc_target}/compile_commands.json" \
           ../../compile_commands.json
@@ -457,6 +462,7 @@ function build_android_target {
            ${BACKEND_DEBUG_FLAG_OPTION} \
            ${STEREOSCOPIC_OPTION} \
            ${ENABLE_PERFETTO} \
+            ${EXCEPTIONS_OPTION} \
            ../..
        ln -sf "out/cmake-android-${lc_target}-${arch}/compile_commands.json" \
           ../../compile_commands.json
@@ -698,6 +704,7 @@ function build_ios_target {
            ${MATDBG_OPTION} \
            ${MATOPT_OPTION} \
            ${STEREOSCOPIC_OPTION} \
+            ${EXCEPTIONS_OPTION} \
            ../..
        ln -sf "out/cmake-ios-${lc_target}-${arch}/compile_commands.json" \
           ../../compile_commands.json
@@ -858,7 +865,7 @@ function check_debug_release_build {

 pushd "$(dirname "$0")" > /dev/null

-while getopts ":hacCfgimp:q:uvWslwedtk:bVx:S:X:Py:" opt; do
+while getopts ":hacCfgimp:q:uvWslwedtk:bVx:S:X:Py:E" opt; do
    case ${opt} in
        h)
            print_help
@@ -1009,6 +1016,9 @@ while getopts ":hacCfgimp:q:uvWslwedtk:bVx:S:X:Py:" opt; do
        P)  ENABLE_PERFETTO="-DFILAMENT_ENABLE_PERFETTO=ON"
            echo "Enabled perfetto"
            ;;
+        E)  EXCEPTIONS_OPTION="-DFILAMENT_ENABLE_EXCEPTIONS=OFF"
+            echo "Disabling exceptions."
+            ;;
        x)  BACKEND_DEBUG_FLAG_OPTION="-DFILAMENT_BACKEND_DEBUG_FLAG=${OPTARG}"
            ;;
        S)  case $(echo "${OPTARG}" | tr '[:upper:]' '[:lower:]') in
--- a/third_party/libassimp/tnt/CMakeLists.txt
+++ b/third_party/libassimp/tnt/CMakeLists.txt
@@ -287,6 +287,7 @@ if(NOT MSVC)
    endif()

    target_compile_options(${TARGET} PRIVATE ${TARGET_FLAGS})
+    target_compile_options(${TARGET} PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-frtti>)
 else()
    target_compile_options(${TARGET} PRIVATE /bigobj)
 endif()