Created attachment 1310 [details]
Patch to generate SDL_KEYDOWN/UP events for dead keys

Pressing dead keys (e.g. ^ or `) on Linux/X11 doesn't generate SDL_KEYDOWN events, pressing another key afterwards (like for composition) just generates a "The key you just pressed is not recognized by SDL. To help get this fixed, please report this to the SDL mailing list <sdl@libsdl.org> X11 KeyCode 0 (-8), X11 KeySym 0x0 ((null))." message.

This is because XFilterEvent() (at the beginning of X11_DispatchEvent() in SDL_x11events.c) returns True for dead keys, so those events are discarded. 
I also found out that XFilterEvents actually changes the events.
(Some more information can be found at http://forums.libsdl.org/viewtopic.php?p=38900#38900 - note that for some reason the forum transformed "â" to "â")


I wrote a patch that in case of KeyPress/KeyRelease events saves the type and the KeyCode and, if XFilterEvent() decides to filter the event, calls SDL_SendKeyboardKey() accordingly.

This yields a similar behavior like SDL2 on Windows: There is a SDL_TEXTINPUT event with the composed char, but there are also two SDL_KEYDOWN events for the keys.

One small issue is that is that the SDL Keycode isn't the same as with the corresponding nodeadkey layout, but seems to be a direct translation of the Scancode.
E.g. on my (german) layout, The ^ key (below Esc) generates a SDL_SCANCODE_GRAVE (`), but a ^ Keycode without dead keys. With dead keys enabled it generates the same Scancode, but a ` Keycode. 
Probably X11 doesn't provide a proper mapping for that key because it's dead anyway, so the default is used.
I think that this is acceptable though and better than no key event at all (like it's the case right now).