Emscripten SDL 2 full screen test.

testfullscreen.c

#include <emscripten/emscripten.h>
#include "SDL.h"

SDL_Window *window = NULL;
SDL_Renderer *renderer = NULL;
SDL_Surface *surface;

//#define USE_SURFACE

/* If window lacks SDL_WINDOW_RESIZABLE, then after exiting from full screen
 * canvas becomes 0x0 in size, and invisible. With that flag and USE_SURFACE,
 * things usually work, but occasionally after switching to full screen
 * nothing is displayed. Re-creating the window fixes both issues.
 * Using only SDL_GetWindowSurface() and SDL_CreateSoftwareRenderer() is
 * insufficient. Re-creating the window also fixes the problem when not
 * using a surface.
 */
void create_window() {
    if (renderer != NULL) {
        SDL_DestroyRenderer(renderer);
        renderer = NULL;
    }
    if (window != NULL) SDL_DestroyWindow(window);
    window = SDL_CreateWindow("Full screen test",
                              SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 
                              640, 480, 0);
}    

void create_renderer() {
#ifdef USE_SURFACE
    surface = SDL_GetWindowSurface(window);
    renderer = SDL_CreateSoftwareRenderer(surface);
#else
    renderer = SDL_CreateRenderer(window, -1, 0);
#endif
}

void draw() {
    static Uint8 red = 0;
    red++;
    SDL_SetRenderDrawColor(renderer, red, 0xFF, 0xFF, 0xFF);
    SDL_RenderClear(renderer);
}

void update() {
#ifdef USE_SURFACE
    SDL_UpdateWindowSurface(window);
#else
    SDL_RenderPresent(renderer);
#endif
}

void loop() {
    SDL_Event e;
    while (SDL_PollEvent(&e)) {
        printf("Event: %i\n", e.type);
        if (e.type == SDL_KEYDOWN) {
            create_window();
            create_renderer();
            printf("Recreated window and renderer: %i\n", (int)renderer);
        }
    }
    draw();
    update();
}

int main(int argc, char *argv[]) {
    SDL_Init(SDL_INIT_VIDEO);
    create_window();
    create_renderer();
    emscripten_set_main_loop(loop, 0, 1);
    SDL_Quit();
    return 0;
}