Backends: OpenGL3: Update loader for Linux to support EGL/GLVND. (#7562)

+ #6983

backends/imgui_impl_opengl3.cpp

@@ -22,6 +22,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2024-05-07: OpenGL: Update loader for Linux to support EGL/GLVND. (#7562)
 //  2024-04-16: OpenGL: Detect ES3 contexts on desktop based on version string, to e.g. avoid calling glPolygonMode() on them. (#7447)
 //  2024-01-09: OpenGL: Update GL3W based imgui_impl_opengl3_loader.h to load "libGL.so" and variants, fixing regression on distros missing a symlink.
 //  2023-11-08: OpenGL: Update GL3W based imgui_impl_opengl3_loader.h to load "libGL.so" instead of "libGL.so.1", accommodating for NetBSD systems having only "libGL.so.3" available. (#6983)

backends/imgui_impl_opengl3_loader.h

@@ -665,31 +665,123 @@ static GL3WglProc get_proc(const char *proc)
 #else
 #include <dlfcn.h>
 
-static void *libgl;
+static void* libgl;  // OpenGL library
-static GL3WglProc (*glx_get_proc_address)(const GLubyte *);
+static void* libglx;  // GLX library
+static void* libegl;  // EGL library
+static GL3WGetProcAddressProc gl_get_proc_address;
 
-static int open_libgl(void)
+static void close_libgl(void)
 {
+    if (libgl) {
+        dlclose(libgl);
+        libgl = NULL;
+    }
+    if (libegl) {
+        dlclose(libegl);
+        libegl = NULL;
+    }
+    if (libglx) {
+        dlclose(libglx);
+        libglx = NULL;
+    }
+}
+
+static int is_library_loaded(const char* name, void** lib)
+{
+    *lib = dlopen(name, RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
+    return *lib != NULL;
+}
+
+static int open_libs(void)
+{
+    // On Linux we have two APIs to get process addresses: EGL and GLX.
+    // EGL is supported under both X11 and Wayland, whereas GLX is X11-specific.
+
+    libgl = NULL;
+    libegl = NULL;
+    libglx = NULL;
+
+    // First check what's already loaded, the windowing library might have
+    // already loaded either EGL or GLX and we want to use the same one.
+
+    if (is_library_loaded("libEGL.so.1", &libegl) ||
+        is_library_loaded("libGLX.so.0", &libglx)) {
+        libgl = dlopen("libOpenGL.so.0", RTLD_LAZY | RTLD_LOCAL);
+        if (libgl)
+            return GL3W_OK;
+        else
+            close_libgl();
+    }
+
+    if (is_library_loaded("libGL.so", &libgl))
+        return GL3W_OK;
+    if (is_library_loaded("libGL.so.1", &libgl))
+        return GL3W_OK;
+    if (is_library_loaded("libGL.so.3", &libgl))
+        return GL3W_OK;
+
+    // Neither is already loaded, so we have to load one.  Try EGL first
+    // because it is supported under both X11 and Wayland.
+
+    // Load OpenGL + EGL
+    libgl = dlopen("libOpenGL.so.0", RTLD_LAZY | RTLD_LOCAL);
+    libegl = dlopen("libEGL.so.1", RTLD_LAZY | RTLD_LOCAL);
+    if (libgl && libegl)
+        return GL3W_OK;
+    else
+        close_libgl();
+
+    // Fall back to legacy libGL, which includes GLX
     // While most systems use libGL.so.1, NetBSD seems to use that libGL.so.3. See https://github.com/ocornut/imgui/issues/6983
     libgl = dlopen("libGL.so", RTLD_LAZY | RTLD_LOCAL);
     if (!libgl)
         libgl = dlopen("libGL.so.1", RTLD_LAZY | RTLD_LOCAL);
     if (!libgl)
         libgl = dlopen("libGL.so.3", RTLD_LAZY | RTLD_LOCAL);
-    if (!libgl)
+
+    if (libgl)
+        return GL3W_OK;
+
     return GL3W_ERROR_LIBRARY_OPEN;
-    *(void **)(&glx_get_proc_address) = dlsym(libgl, "glXGetProcAddressARB");
+}
+
+static int open_libgl(void)
+{
+    int res = open_libs();
+    if (res)
+        return res;
+
+    if (libegl)
+        *(void**)(&gl_get_proc_address) = dlsym(libegl, "eglGetProcAddress");
+    else if (libglx)
+        *(void**)(&gl_get_proc_address) = dlsym(libglx, "glXGetProcAddressARB");
+    else
+        *(void**)(&gl_get_proc_address) = dlsym(libgl, "glXGetProcAddressARB");
+
+    if (!gl_get_proc_address) {
+        close_libgl();
+        return GL3W_ERROR_LIBRARY_OPEN;
+    }
+
     return GL3W_OK;
 }
 
-static void close_libgl(void) { dlclose(libgl); }
+static GL3WglProc get_proc(const char* proc)
-
-static GL3WglProc get_proc(const char *proc)
 {
-    GL3WglProc res;
+    GL3WglProc res = NULL;
-    res = glx_get_proc_address((const GLubyte *)proc);
+
+    // Before EGL version 1.5, eglGetProcAddress doesn't support querying core
+    // functions and may return a dummy function if we try, so try to load the
+    // function from the GL library directly first.
+    if (libegl)
+        *(void**)(&res) = dlsym(libgl, proc);
+
     if (!res)
-        *(void **)(&res) = dlsym(libgl, proc);
+        res = gl_get_proc_address(proc);
+
+    if (!libegl && !res)
+        *(void**)(&res) = dlsym(libgl, proc);
+
     return res;
 }
 #endif

docs/CHANGELOG.txt

@@ -80,6 +80,7 @@ Other changes:
   mitigitate issues with reading vertex indexing limits with 16-bit indices. (#7496, #5720)
 - Backends: OpenGL3: Detect ES3 contexts on desktop based on version string,
   to e.g. avoid calling glPolygonMode() on them. (#7447) [@afraidofdark, @ocornut]
+- Backends: OpenGL3: Update loader for Linux to support EGL/GLVND. (#7562) [@ShadowNinja, @vanfanel]
 - Backends: Vulkan: Added convenience support for Volk via IMGUI_IMPL_VULKAN_USE_VOLK define.
   (you could always use IMGUI_IMPL_VULKAN_NO_PROTOTYPES + ImGui_ImplVulkan_LoadFunctions() as well).
   (#6582, #4854) [@adalsteinnh, @kennyalive, @ocornut]