Multi threaded screenshot

SDL Development
1

When I take a screenshot in my simple pong game the game freezes for half a second while taking the screenshot. I’ve tried making it a multi threaded function, but “SDL_RenderReadPixels()” almost always makes my game crash. The console output on crash is “i965: Failed to submit batchbuffer: Invalid argument” on my laptop (Asus X55A) on Fedora 33.

int pong_Screenshot(void *renderer)
{
        SDL_Surface *sshot = SDL_CreateRGBSurface(0, w, h, 32, BLACK);
        SDL_RenderReadPixels((SDL_Renderer *)renderer, NULL, 0, sshot->pixels, sshot->pitch);
        char text[30];
        time_t now = time(NULL);
        struct tm *t = localtime(&now);
        strftime(text, sizeof(text), "%d-%m-%Y_%H-%M-%S.bmp", t);
        SDL_SaveBMP(sshot, text);
        SDL_FreeSurface(sshot);
        return 0;
}

The code block above doesn’t crash if not used on a separate thread.

2

You could keep the SaveBMP call on a separate thread, but SDL_Render APIs can only be used on the main thread.

3

Thanks for the info. This is how I wrote the screenshot function:

int pong_SaveFile(void *surface)
{
        char filename[30];
        time_t now = time(NULL);
        struct tm *t = localtime(&now);
        strftime(filename, sizeof(filename), "%d-%m-%Y_%H-%M-%S.png", t);

        FILE *file = fopen(filename, "r");
        if (file  == NULL)
                IMG_SavePNG((SDL_Surface *) surface, filename);
        else
                fclose(file);

        SDL_FreeSurface((SDL_Surface *) surface);
        return 0;
}

void pong_Screenshot(SDL_Renderer *renderer)
{
        int width = 0, height = 0;
        SDL_GetRendererOutputSize(renderer , &width, &height);

        SDL_Surface *screenshot = SDL_CreateRGBSurface(0, width, height, 32, BLACK);
        SDL_RenderReadPixels(renderer, NULL, 0, screenshot->pixels, screenshot->pitch);

        SDL_Thread *thread = SDL_CreateThread(pong_SaveFile, "SaveFile", (void *) screenshot);
        SDL_DetachThread(thread);
}

Is there anything I can do to improve this in terms of multi threading?