test-threads.cpp

//
// Compile with: em++ test-threads.cpp -o test-threads.html -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=2 -s USE_SDL=2
//
// Expected behavior: program starts with a black screen, smoothly fades it to
// green, then resets (show black screen, fades-in green, rinse and repeat).
//

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <SDL.h>
#include <unistd.h>

#define GL_GLEXT_PROTOTYPES 1
#include <SDL_opengles2.h>

static pthread_t thread = 0;
static SDL_Window * window = 0;
static SDL_GLContext gl = 0;

void * thread_main(void *) {
    while (true) {
        if (SDL_GL_MakeCurrent(window, gl) < 0) {
            printf("SDL_GL_MakeCurrent failed: %s\n", SDL_GetError());
        } else {
            GLfloat value = ((GLfloat)((SDL_GetTicks() / 25) % 255)) / 255.0f;
            glClearColor(0, value, 0, 1);
            glClear(GL_COLOR_BUFFER_BIT);
            SDL_GL_SwapWindow(window);
        }

        // Commenting out the usleep(1000) call can cause Chrome to hang
        usleep(1000);   // sleep for 1ms (aka. 1000 us)
    }
    return 0;
}

int main() {
    // Use OpenGL ES 2.0
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);

    // Init SDL
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS) != 0) {
        printf("SDL_Init failed: %s\n", SDL_GetError());
        return 1;
    }
    window = SDL_CreateWindow(
        "Thread Test",
        SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
        640, 480,
        SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE
    );
    if (!window) {
        printf("SDL_CreateWindow failed: %s\n", SDL_GetError());
        return 1;
    }
    gl = SDL_GL_CreateContext(window);
    if (!gl) {
        printf("SDL_GL_CreateContext failed: %s\n", SDL_GetError());
        return 1;
    }

    // Spin off separate thread
    if (pthread_create(&thread, NULL, thread_main, NULL) != 0) {
        printf("pthread_create failed\n");
        return 1;
    }
}