CODEWITHSUNDEEP
c++eventsevent-handlingsdl-2
user8110081
user8110081

Reputation:

cant get SDL2 event's from window

I my trying to learn SDL in C++ . I have simple program which will display a image . but When I try to close window by clicking close button on the window nothing happens.

here is my code:-

#include <SDL2/SDL.h>
int main(int argc,char **argv)
{
    static int k =0;
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window *w;
    w = SDL_CreateWindow("SDL VS Works",300,300,400,500,SDL_WINDOW_OPENGL);

    SDL_Renderer *render = SDL_CreateRenderer(w,-1,SDL_RENDERER_ACCELERATED);

    SDL_Surface *tux  = SDL_LoadBMP("res/tux.bmp");

    SDL_Texture *texture = SDL_CreateTextureFromSurface(render,tux);
    SDL_FreeSurface(tux);
    SDL_ShowWindow(w);
    SDL_Event event;

    while(1)
    {
        k++;
        printf("Running and loop %d\'th\n",k);
        SDL_PollEvent(&event);
        if(event.type == SDL_QUIT)
        {
            printf("closing \n");
            goto sos;
        }
        SDL_RenderCopy(render,texture,0,0);
        SDL_RenderPresent(render);
        SDL_Delay(1000);

    }


sos:
    SDL_DestroyWindow(w);
    SDL_DestroyRenderer(render);
    SDL_DestroyTexture(texture);

    SDL_Quit();
}

I am using g++ 7.3 on Arch Linux.

Upvotes: 0

Views: 1137

Answers (2)

Zebrafish
Zebrafish

Reputation: 13886

By the way, the loop should look something like this:

SDL_Event SDLEvent;

    while (SDL_PollEvent(&SDLEvent))
    {
        switch (SDLEvent.type)
        {
        case SDL_QUIT: break;
        case SDL_WINDOWEVENT: break;
        case SDL_MOUSEMOTION: break;
        case SDL_MOUSEWHEEL: break;
        }
    }

Whether it's a switch statement like this or an if statement like you have isn't important. SDL_PollEvents will return 1 if there are still events in the queue, or zero otherwise. By calling the SDL_PollEvents(&SDLEvent) inside the while condition it will handle all the events in the queue before entering the while block next.

Interestingly your problem that your window won't close seems to be related to something else because it works for me. I've already mentioned maybe get rid of the SDL_Delay line and see if that does anything;

Upvotes: 1

Nelfeal
Nelfeal

Reputation: 13269

The SDL uses an event queue internally. When any event occurs, like the mouse moving a few pixels, it gets added to the queue. When you poll for events (using SDL_PollEvent), you only get the oldest event. Everything else stays in the queue.

Since your code only polls once per second, the queue probably gets flooded by mouse movements, and the SDL_QUIT event is just waiting in line, deep into the queue.

What you usually want to do is poll for events in a loop. Note that SDL_PollEvent returns 0 when there is no pending event.

while (SDL_PollEvent(&event)) {
    if(event.type == SDL_QUIT)
    {
        //...
    }
}

Upvotes: 1

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