How to correctly handle control-key combinations in SDL2

Question

In my SDL 2.0 based application, I would like to handle both Control + and Control =.

I understand that I could handle the SDL_KEYDOWN event and look for the SDLK_EQUALS keycode in combination with KEYMODE_CTRL. And even check for KEYMOD_SHIFT' to distinguish between+and=`. However, this is not portable and breaks on keyboards where those symbols are mapped to different keys.

Another thing I have tried is to enable SDL_StartTextInput() and then listen to SDL_TEXTINPUT events. However that only works for printable characters. It ignores control sequences completely.

What is the correct the way to do this? I see SDL 1.2 actually had a unicode field in the SDL_Keysym structure. That would definitely make this a lot easier for me. Does anyone know why that was removed and what the equivalent in SDL 2.0 would be?

I think it was replaced by text input events, take a look at https://wiki.libsdl.org/Tutorials/TextInput — keltar, Jan 10 '17 at 15:37
@keltar the problem is that the TextInput swallows the control keys.It only works for printable characters. I can read the code to see how it works internally and maybe build something similar, but I'd prefer to not do that. — Stefan Arentz, Jan 10 '17 at 16:49
But you still have keydown events for ctrl if it isn't part of input sequence, so you can combine both. — keltar, Jan 10 '17 at 17:44
@keltar I don't get `SDL_TEXTINPUT` events for non printable control characters. Like `C-+`. — Stefan Arentz, Jan 10 '17 at 18:05
But you have one for `+` and `SDL_KEYDOWN` for ctrl, right? (at least I do) — keltar, Jan 10 '17 at 18:17
@keltar can you show some code? I don't understand how I can recognize `+` in `SDL_KEYDOWN`. — Stefan Arentz, Jan 10 '17 at 18:19
@StefanArentz Can you please check my questions [Link1](http://stackoverflow.com/questions/41217020/wkwebview-didt-give-all-cookies-in-navigationresponse) [Link2](http://stackoverflow.com/questions/43154918/share-wkwebview-cookies-with-uiwebview). I think you can give me answer. — ZAFAR007, Apr 04 '17 at 13:27

score 6 · Accepted Answer · edited Dec 22 '22 at 17:31

Here is an example how you can get unicode input as SDL_TEXTINPUT but the rest as SDL_KEYDOWN:

#include "SDL.h"
#include <stdio.h>

int main(int argc, char *argv[]) {
    int done = 0;
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window *w = SDL_CreateWindow("foo", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
            640, 480, 0);

    int lctrl = 0, rctrl = 0;

    SDL_StartTextInput();
    while (!done) {
        SDL_Event event;
        while(SDL_PollEvent(&event)) {
            switch (event.type) {
            case SDL_QUIT:
                done = 1;
                break;
            case SDL_TEXTINPUT: {
                int ctrl_state = lctrl || rctrl;
                printf("%s, ctrl %s\n", event.text.text, (ctrl_state) ? "pressed" : "released");
            } break;
            case SDL_KEYDOWN:
                if(event.key.keysym.sym == SDLK_RCTRL) { rctrl = 1; }
                else if(event.key.keysym.sym == SDLK_LCTRL) { lctrl = 1; }
                break;
            case SDL_KEYUP:
                if(event.key.keysym.sym == SDLK_RCTRL) { rctrl = 0; }
                else if(event.key.keysym.sym == SDLK_LCTRL) { lctrl = 0; }
                break;
            }
        }
        SDL_UpdateWindowSurface(w);
    }

    SDL_Quit();

    return 0;
}

To simplify things, it ignores SDL_TEXTEDITING, which may (or not) be what you want. Also SDL_GetKeyboardState can be used instead of manually processing events and accumulating modifier keys flags, with the same result.

That's really great example. But maybe you'd want to add `#include ` to make it perfect... — Zvika, May 04 '20 at 09:55

How to correctly handle control-key combinations in SDL2

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