em_sdl_key_sample.cxx

#ifdef EMSCRIPTEN
  #include <emscripten/emscripten.h>
  #include <SDL/SDL.h>
#else
  #include <SDL2/SDL.h>
#endif

#include <iostream>
#include <cstdint>
#include <thread>
#include <chrono>

auto main() -> int
{
  SDL_Init
  ( SDL_INIT_VIDEO
#if SDL_MAJOR_VERSION >= 2
  | SDL_INIT_EVENTS
#endif
  );

  constexpr int window_width_in_px  = 320;
  constexpr int window_height_in_px = 240;
#if SDL_MAJOR_VERSION >= 2
  auto window
    = SDL_CreateWindow("sdl", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, window_width_in_px, window_height_in_px, SDL_WINDOW_OPENGL);
#else
  auto surface
    = SDL_SetVideoMode(window_width_in_px, window_height_in_px, 32, SDL_OPENGL);
#endif
  using key_states_t = const std::uint8_t*;
#ifndef EMSCRIPTEN
  key_states_t key_states;
  do
  {
#else
  emscripten_set_main_loop([]
  {
    key_states_t key_states;
#endif
    SDL_PumpEvents();
    key_states = SDL_GetKeyboardState(nullptr);
    std::uint_fast8_t pressed_key_count = 0;
    // comment out reason to see: https://github.com/kripken/emscripten/issues/2283
    for ( auto code = /*SDL_SCANCODE_A*/0; code < /*SDL_SCANCODE_Z*/255; ++code )
      if ( key_states[ code ] )
      {
        ++pressed_key_count;
        std::cerr << code << " ";
      }
    if ( pressed_key_count )
      std::cerr << "\n";
#ifndef EMSCRIPTEN
    std::this_thread::sleep_for( std::chrono::milliseconds(100) );
  }
  while( ! key_states[ SDL_SCANCODE_ESCAPE ] );
#else
  }, 0, 1);
#endif
#if SDL_MAJOR_VERSION >= 2
  SDL_DestroyWindow(window);
#endif
  SDL_Quit();
}