Add a FILAMENT_SUPPORTS_OPENGL CMake option (#3966)

BUILDING.md

@@ -84,6 +84,7 @@ The following CMake options are boolean options specific to Filament:
 - `FILAMENT_ENABLE_JAVA`:          Compile Java projects: requires a JDK and the JAVA_HOME env var
 - `FILAMENT_ENABLE_LTO`:           Enable link-time optimizations if supported by the compiler
 - `FILAMENT_BUILD_FILAMAT`:        Build filamat and JNI buildings
+- `FILAMENT_SUPPORTS_OPENGL`:      Include the OpenGL backend
 - `FILAMENT_SUPPORTS_METAL`:       Include the Metal backend
 - `FILAMENT_SUPPORTS_VULKAN`:      Include the Vulkan backend
 - `FILAMENT_INSTALL_BACKEND_TEST`: Install the backend test library so it can be consumed on iOS

CMakeLists.txt

@@ -369,6 +369,12 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug" OR CMAKE_BUILD_TYPE STREQUAL "RelWithDebIn
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DTNT_DEV")
 endif()
 
+# By default, build with support for OpenGL on all platforms.
+option(FILAMENT_SUPPORTS_OPENGL "Include the OpenGL backend" ON)
+if (FILAMENT_SUPPORTS_OPENGL)
+    add_definitions(-DFILAMENT_SUPPORTS_OPENGL)
+endif()
+
 # By default, build with Vulkan support on desktop platforms, although clients must request to use
 # it at run time.
 if (WIN32 OR WEBGL OR IOS)
@@ -424,9 +430,9 @@ endif()
 
 set(MATC_API_FLAGS )
 
-# TODO: Add a flag to build Filament without support for OpenGL.
-set(MATC_API_FLAGS ${MATC_API_FLAGS} -a opengl)
-
+if (FILAMENT_SUPPORTS_OPENGL)
+    set(MATC_API_FLAGS ${MATC_API_FLAGS} -a opengl)
+endif()
 if (FILAMENT_SUPPORTS_VULKAN)
     set(MATC_API_FLAGS ${MATC_API_FLAGS} -a vulkan)
 endif()
@@ -643,7 +649,9 @@ if (WEBGL)
 endif()
 
 if (IS_HOST_PLATFORM)
-    add_subdirectory(${LIBRARIES}/bluegl)
+    if (FILAMENT_SUPPORTS_OPENGL)
+        add_subdirectory(${LIBRARIES}/bluegl)
+    endif()
     add_subdirectory(${LIBRARIES}/filamentapp)
     add_subdirectory(${LIBRARIES}/imageio)
 

filament/backend/CMakeLists.txt

@@ -55,7 +55,7 @@ set(PRIVATE_HDRS
 # OpenGL / OpenGL ES Sources
 # ==================================================================================================
 
-if (NOT FILAMENT_USE_EXTERNAL_GLES3 AND NOT FILAMENT_USE_SWIFTSHADER)
+if (FILAMENT_SUPPORTS_OPENGL AND NOT FILAMENT_USE_EXTERNAL_GLES3 AND NOT FILAMENT_USE_SWIFTSHADER)
     list(APPEND SRCS
             src/opengl/gl_headers.cpp
             src/opengl/gl_headers.h
@@ -255,7 +255,10 @@ add_library(vkshaders STATIC ${DUMMY_SRC} ${RESGEN_SOURCE})
 # ==================================================================================================
 
 if (ANDROID)
-    target_link_libraries(${TARGET} PUBLIC GLESv3 EGL android)
+    if (FILAMENT_SUPPORTS_OPENGL)
+        target_link_libraries(${TARGET} PUBLIC GLESv3 EGL)
+    endif()
+    target_link_libraries(${TARGET} PUBLIC android)
 endif()
 
 if (FILAMENT_USE_SWIFTSHADER)
@@ -270,7 +273,7 @@ target_link_libraries(${TARGET} PUBLIC math)
 target_link_libraries(${TARGET} PUBLIC utils)
 
 # Android, iOS, and WebGL do not use bluegl.
-if(NOT IOS AND NOT ANDROID AND NOT WEBGL)
+if(FILAMENT_SUPPORTS_OPENGL AND NOT IOS AND NOT ANDROID AND NOT WEBGL)
     target_link_libraries(${TARGET} PRIVATE bluegl)
 endif()
 

filament/backend/src/Platform.cpp

@@ -20,44 +20,44 @@
 #include <utils/debug.h>
 
 #if defined(ANDROID)
-    #ifndef FILAMENT_USE_EXTERNAL_GLES3
+    #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3)
         #include "opengl/PlatformEGLAndroid.h"
     #endif
-    #if defined (FILAMENT_DRIVER_SUPPORTS_VULKAN)
+    #if defined(FILAMENT_DRIVER_SUPPORTS_VULKAN)
         #include "vulkan/PlatformVkAndroid.h"
     #endif
 #elif defined(IOS)
-    #ifndef FILAMENT_USE_EXTERNAL_GLES3
+    #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3)
         #include "opengl/PlatformCocoaTouchGL.h"
     #endif
-    #if defined (FILAMENT_DRIVER_SUPPORTS_VULKAN)
+    #if defined(FILAMENT_DRIVER_SUPPORTS_VULKAN)
         #include "vulkan/PlatformVkCocoaTouch.h"
     #endif
 #elif defined(__APPLE__)
-    #if !defined(FILAMENT_USE_EXTERNAL_GLES3) && !defined(FILAMENT_USE_SWIFTSHADER)
+    #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3) && !defined(FILAMENT_USE_SWIFTSHADER)
         #include "opengl/PlatformCocoaGL.h"
     #endif
-    #if defined (FILAMENT_DRIVER_SUPPORTS_VULKAN)
+    #if defined(FILAMENT_DRIVER_SUPPORTS_VULKAN)
         #include "vulkan/PlatformVkCocoa.h"
     #endif
 #elif defined(__linux__)
-    #if !defined(FILAMENT_USE_EXTERNAL_GLES3) && !defined(FILAMENT_USE_SWIFTSHADER)
+    #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3) && !defined(FILAMENT_USE_SWIFTSHADER)
         #include "opengl/PlatformGLX.h"
     #endif
     #if defined (FILAMENT_DRIVER_SUPPORTS_VULKAN)
         #include "vulkan/PlatformVkLinux.h"
     #endif
 #elif defined(WIN32)
-    #if !defined(FILAMENT_USE_EXTERNAL_GLES3) && !defined(FILAMENT_USE_SWIFTSHADER)
+    #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3) && !defined(FILAMENT_USE_SWIFTSHADER)
         #include "opengl/PlatformWGL.h"
     #endif
-    #if defined (FILAMENT_DRIVER_SUPPORTS_VULKAN)
+    #if defined(FILAMENT_DRIVER_SUPPORTS_VULKAN)
         #include "vulkan/PlatformVkWindows.h"
     #endif
 #elif defined(__EMSCRIPTEN__)
     #include "opengl/PlatformWebGL.h"
 #else
-    #ifndef FILAMENT_USE_EXTERNAL_GLES3
+    #if defined(FILAMENT_SUPPORTS_OPENGL) && !defined(FILAMENT_USE_EXTERNAL_GLES3)
         #include "opengl/PlatformDummyGL.h"
     #endif
 #endif
@@ -112,22 +112,27 @@ DefaultPlatform* DefaultPlatform::create(Backend* backend) noexcept {
         return nullptr;
 #endif
     }
-    #if defined(FILAMENT_USE_EXTERNAL_GLES3) || defined(FILAMENT_USE_SWIFTSHADER)
-        return nullptr;
-    #elif defined(ANDROID)
-        return new PlatformEGLAndroid();
-    #elif defined(IOS)
-        return new PlatformCocoaTouchGL();
-    #elif defined(__APPLE__)
-        return new PlatformCocoaGL();
-    #elif defined(__linux__)
-        return new PlatformGLX();
-    #elif defined(WIN32)
-        return new PlatformWGL();
-    #elif defined(__EMSCRIPTEN__)
-        return new PlatformWebGL();
+    assert_invariant(*backend == Backend::OPENGL);
+    #if defined(FILAMENT_SUPPORTS_OPENGL)
+        #if defined(FILAMENT_USE_EXTERNAL_GLES3) || defined(FILAMENT_USE_SWIFTSHADER)
+            return nullptr;
+        #elif defined(ANDROID)
+            return new PlatformEGLAndroid();
+        #elif defined(IOS)
+            return new PlatformCocoaTouchGL();
+        #elif defined(__APPLE__)
+            return new PlatformCocoaGL();
+        #elif defined(__linux__)
+            return new PlatformGLX();
+        #elif defined(WIN32)
+            return new PlatformWGL();
+        #elif defined(__EMSCRIPTEN__)
+            return new PlatformWebGL();
+        #else
+            return new PlatformDummyGL();
+        #endif
     #else
-        return new PlatformDummyGL();
+        return nullptr;
     #endif
 }