SDL2 does not render properly after window resize

Question

I can't draw on the window after increasing its size. I can still draw on the old part. For instance, I have a 100x100 window, I increase its size with SDL_SetWindowSize to 200x200. I can draw to the old 100x100 zone, but the new zone is not usable unless I use a delay before using it.

Here is an example of the problem using SDL_RenderClear:

int main(void)
{
        SDL_Init(SDL_INIT_VIDEO);

        SDL_Window *win = SDL_CreateWindow("test", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 100, 100, SDL_WINDOW_SHOWN);
        SDL_Renderer *rend = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED);

        /* Draw red window */
        SDL_SetRenderDrawColor(rend, 255, 0, 0, 255);
        SDL_RenderClear(rend);
        SDL_RenderPresent(rend); // Completely red

        SDL_Delay(3000);

        /* Increase window size and draw it green */
        SDL_SetWindowSize(win, 800, 800);
        SDL_SetRenderDrawColor(rend, 0, 255,0, 255);
        SDL_RenderClear(rend);
        SDL_RenderPresent(rend); // Partially green

        SDL_Delay(3000);

        /* Make window blue */
        SDL_SetRenderDrawColor(rend, 0, 0, 255, 255);
        SDL_RenderClear(rend);
        SDL_RenderPresent(rend); // Completely blue

        SDL_Delay(3000);

        SDL_DestroyRenderer(rend);
        SDL_DestroyWindow(win);
        SDL_Quit();
        return 0;
}

This code is supposed to:

Create a 100x100 window and color it red then waits 3s.
Increase the window size to 800x800 and color it in green then waits 3s.
Color the same window in blue then waits 3s.

The code actually does:

Create a 100x100 window and color it red then waits 3s.
Increase the window size to 800x800 and color only a 100x100 square in green then waits 3s.
Color the same window in blue then waits 3s.

When I add a 100ms delay before SDL_RenderPresent(), it works properly. However, I have the same problem on one of my project, and I have to use a 200ms delay for it to work.

Why do I need a delay before rendering? Is there any way to know how much time to wait before SDL_RenderPresent()?

Try using an actual SDL_PollEvent()/SDL_WaitEvent() loop, or at least SDL_PumpEvents(); SDL_Delay() and hoping for the best is pretty iffy on modern composited windowing systems. — genpfault

isocppforbids isocppforbids · Accepted Answer · 2020-01-19T16:32:37

I found out your problem!

When you create your window, you need to pass the flag SDL_WINDOW_RESIZABLE. Like this:

    SDL_Window *win = SDL_CreateWindow("test", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 100, 100, SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE );

Make this change and your window will behave correctly.

SDL2 does not render properly after window resize

1 Answers