NOT A BUG: HOWTO - SDL3 and Textbox

[linkdd]

First, thanks for the great work.

The demo is based on SDL2, but now SDL3 is generally available.

One key change between SDL2 and SDL3 has an impact on Textbox:

https://wiki.libsdl.org/SDL2/SDL_StartTextInput

On desktop platforms, SDL_StartTextInput() is implicitly called on SDL video subsystem initialization which will cause SDL_TextInputEvent and SDL_TextEditingEvent to begin emitting.

https://wiki.libsdl.org/SDL3/SDL_StartTextInput

Text input events are not received by default.

After calling mu_end(ctx), we need to check the ctx->focus variable (which, if true, means that some element wants to handle keyboard events) and enable/disable SDL's text input events:

mu_end(ctx);

if (ctx->focus != 0) {
    SDL_StartTextInput(window);
}
else {
    SDL_StopTextInput(window);
}

I'll leave that here in case someone else have the same problem.