Add support for EGL on Linux

gl3w_gen.py

@@ -253,31 +253,114 @@ def download(url, dst):
 #else
 #include <dlfcn.h>
 
-static void *libgl;
-static GL3WglProc (*glx_get_proc_address)(const GLubyte *);
+static void *libgl;  // OpenGL library
+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.1", &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
 	libgl = dlopen("libGL.so.1", RTLD_LAZY | RTLD_LOCAL);
-	if (!libgl)
-		return GL3W_ERROR_LIBRARY_OPEN;
+	
+	if (libgl)
+		return GL3W_OK;
 
-	*(void **)(&glx_get_proc_address) = dlsym(libgl, "glXGetProcAddressARB");
-	return GL3W_OK;
+	return GL3W_ERROR_LIBRARY_OPEN;
 }
 
-static void close_libgl(void)
+static int open_libgl(void)
 {
-	dlclose(libgl);
+	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 GL3WglProc get_proc(const char *proc)
 {
-	GL3WglProc res;
+	GL3WglProc res = NULL;
+
+	// 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);
 
-	res = glx_get_proc_address((const GLubyte *)proc);
 	if (!res)
+		res = gl_get_proc_address(proc);
+
+	if (!libegl && !res)
 		*(void **)(&res) = dlsym(libgl, proc);
+
 	return res;
 }
 #endif