I am trying to build a C++/CMake app with SDL3 as git submodule on Ubuntu 24.04, but it cannot configure OpenGL support. I follow the example and add the SDL_OpenGL=ON option and the path to libGL.so (just in case):
git submodule add git@github.com:libsdl-org/SDL.git lib/SDL
CMakeLists.txt:
...
set(SDL_OPENGL ON)
set(SDL_OPENGLES OFF)
list(APPEND CMAKE_PREFIX_PATH "/usr/lib/x86_64-linux-gnu/")
# that's where libGL.so sits:
# /usr/lib/x86_64-linux-gnu/libGL.so
add_subdirectory(lib/SDL EXCLUDE_FROM_ALL)
...
target_link_libraries(mylib PRIVATE SDL3::SDL3)
At CMake configuration, it does not seem to find OpenGL:
$ cmake -DCMAKE_BUILD_TYPE=Debug -S./ -B./build -G Ninja
...
-- SDL3 was configured with the following options:
--
-- Platform: Linux-6.8.0-47-generic
-- 64-bit: TRUE
-- Compiler: /usr/bin/cc
-- Revision: SDL3-3.3.0-release-3.2.6-18-g2c7c3d4d7
-- Vendor:
--
-- Subsystems:
-- <all ON>
--
-- Options:
...
-- SDL_OPENGL (Wanted: ON): OFF
-- SDL_OPENGLES (Wanted: OFF): OFF
...
--
-- If something was not detected, although the libraries
-- were installed, then make sure you have set the
-- CMAKE_C_FLAGS and CMAKE_PREFIX_PATH CMake variables correctly.
...
It does not say anything else about OpenGL during CMake configuration. It complains about not finding LibUSB and FFmpeg. But nothing about OpenGL.
And at runtime it indeed fails on window creation with SDL_WINDOW_OPENGL flag in a constructor that sets up the SDL context like this:
#define macro_test_critical(condition, log_fail_message) \
if (condition) { \
log(log_level::CRITICAL, (log_fail_message)); \
exit(1); \
}
SDL_Window *gSDLWindow{nullptr}; // a private member
ContextSDL::ContextSDL() {
macro_test_critical(SDL_Init(SDL_INIT_VIDEO) < 0, "SDL_INIT_VIDEO failed") else {
log(log_level::DEBUG, "SDL_INIT_VIDEO success");
}
// prepare OpenGL attributes
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 6);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
// multisampling for anti-aliasing
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 4);
gSDLWindow = SDL_CreateWindow("OpenGL Window",
m_ScreenWidth, m_ScreenHeight,
SDL_WINDOW_OPENGL);
macro_test_critical(gSDLWindow == nullptr,
std::string("SDL_CreateWindow failed: ") + std::string(SDL_GetError())) else {
log(log_level::DEBUG, "ContextSDL::ContextSDL created OpenGL window");
}
...
}
The error is "SDL not configured with OpenGL/GLX support":
$ ./main
log level 1: ContextSDL::ContextSDL(int, int) at /....cpp:26 SDL_INIT_VIDEO success
log level 5: ContextSDL::ContextSDL(int, int) at /....cpp:51 SDL_CreateWindow failed: SDL not configured with OpenGL/GLX support
I think that OpenGL is there:
$ glxinfo | grep OpenGL
OpenGL vendor string: AMD
OpenGL renderer string: AMD Radeon Graphics (radeonsi, renoir, LLVM 19.1.1, DRM 3.59, 6.11.0-17-generic)
OpenGL core profile version string: 4.6 (Core Profile) Mesa 24.2.8-1ubuntu1~24.04.1
OpenGL core profile shading language version string: 4.60
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile
OpenGL core profile extensions:
OpenGL version string: 4.6 (Compatibility Profile) Mesa 24.2.8-1ubuntu1~24.04.1
OpenGL shading language version string: 4.60
OpenGL context flags: (none)
OpenGL profile mask: compatibility profile
OpenGL extensions:
OpenGL ES profile version string: OpenGL ES 3.2 Mesa 24.2.8-1ubuntu1~24.04.1
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.20
OpenGL ES profile extensions:
The graphics driver is amdgpu.
I've installed all suggested build dependencies of SDL. And these libraries are installed:
$ sudo apt install libgl-dev libglx-dev mesa-common-dev mesa-utils freeglut3-dev
...
libgl-dev is already the newest version (1.7.0-1build1).
libglx-dev is already the newest version (1.7.0-1build1).
mesa-common-dev is already the newest version (24.2.8-1ubuntu1~24.04.1).
mesa-utils is already the newest version (9.0.0-2).
freeglut3-dev is already the newest version (3.4.0-1build1).
...
How to make it find and configure OpenGL? Does it miss some library, some path?
Update:
echo $XDG_SESSION_TYPE says so and there is nothing in env | grep -i wayl./usr/include/:
find /usr/include -name "gl.h"
/usr/include/GL/gl.h
/usr/include/GLES/gl.h
/usr/include/epoxy/gl.h
--trace pointed at the error. It looks like something goes wrong in the SDL cmake macros when the CMP0126 policy is not set. And by setting it to OLD I got the program to run. I would post it as an answer if the question got reopened.No, this was not causing the problem. I moved the final update to the answer.
It looks like I just forgot to clear the CMake build at some point. This program was built with SDL2 before. I am pretty sure to have removed the build directory and rebuilt it from scratch with SDL3. Probably, I did not remove build/ directory after installing something later. Although, everything was "already the newest version" in the install commands.
In any case, I cannot reproduce it by changing that policy back and forth. It does not matter. (And it should not.)
More details from running cmake with --trace:
The OpenGL build is triggered by HAVE_OPENGL option in the SDL CMake project. The build macros (cmake/sdlchecks.cmake) test for OpenGL with check_c_source_compiles(... HAVE_OPENGL) in order to set the HAVE_OPENGL variable. If the variable is already defined, the check is skipped inside the check_c_source_compiles. In the --trace log, you can see it failing to confirm that NOT DEFINED HAVE_OPENGL like this:
.../SDL/CMakeLists.txt(1589): CheckOpenGL()
.../SDL/cmake/sdlchecks.cmake(723): if(SDL_OPENGL )
.../SDL/cmake/sdlchecks.cmake(724): check_c_source_compiles(
...
... HAVE_OPENGL )
/usr/share/cmake-3.28/Modules/Internal/CheckSourceCompiles.cmake(11):
if(NOT DEFINED ${_var} ) # <-- _var is HAVE_OPENGL here
.../SDL/cmake/sdlchecks.cmake(728): if(HAVE_OPENGL )
Then it is supposed to set SDL_VIDEO_OPENGL 1 under if(HAVE_OPENGL) branch like this:
# cmake/sdlchecks.cmake
macro(CheckOpenGL)
if(SDL_OPENGL)
check_c_source_compiles("..." HAVE_OPENGL)
if(HAVE_OPENGL)
set(SDL_VIDEO_OPENGL 1)
set(SDL_VIDEO_RENDERER_OGL 1)
endif()
endif()
endmacro()
if(HAVE_OPENGL) tests the contents of the variable. In the problematic old build, HAVE_OPENGL and HAVE_OPENGL_GLX are set to empty strings in the CMakeCache.txt like this:
//Test HAVE_OPENGL
HAVE_OPENGL:INTERNAL=
//Test HAVE_OPENGLES_V1
...
//Test HAVE_OPENGL_GLX
HAVE_OPENGL_GLX:INTERNAL=
CMake must have skipped setting the SDL_VIDEO_OPENGL because of HAVE_OPENGL= in the cache. In the new build CMakeCache.txt it is set to 1, so the if(HAVE_OPENGL) sets SDL_VIDEO_OPENGL and builds with OpenGL fine:
HAVE_OPENGL:INTERNAL=1
If I modify the new build/CMakeCache.txt manually to HAVE_OPENGL:INTERNAL=, I do get the original SDL_OPENGL OFF in the CMake config log. And if I also modify HAVE_OPENGL_GLX:INTERNAL= and rebuild, the program does not find OpenGL at runtime.