SDL2, Windows: Window title bar flashing while changing focus of borderless window on Windows

[Majjcom]

I created a borderless window with SDL and set it to be always on top with a semi-transparent property. When I change its focus using the mouse, theoretically, there should be no title bar on it, but for a moment, the title bar appears. It's really strange.

Here are some screen shots:

It should be like this:

But for a moment, it changes to this appearance:

[slouken]

Can you reproduce this the SDL test programs, or provide a minimal example that helps us reproduce this?

[Majjcom]

#include <SDL.h>
#include <iostream>

using namespace std;

int main(int argc, char* argv[])
{
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS))
    {
        cout << "SDL init error: " << SDL_GetError() << endl;
        return 0;
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

    SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);

    SDL_Window* window = SDL_CreateWindow(
        "Test Window",
        SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
        800, 600,
        SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE | SDL_WINDOW_SKIP_TASKBAR
    );

    if (!window)
    {
        cout << "SDL create window failed: " << SDL_GetError() << endl;
        SDL_Quit();
        return 0;
    }

    SDL_GLContext gc = SDL_GL_CreateContext(window);

    SDL_SetWindowBordered(window, SDL_FALSE);

    SDL_SetWindowAlwaysOnTop(window, SDL_TRUE);

    //if (!gladLoadGLES2Loader((GLADloadproc)SDL_GL_GetProcAddress))
    //{
    //    SDL_GL_DeleteContext(gc);
    //    SDL_DestroyWindow(window);
    //    SDL_Quit();
    //    cout << "Load GL ProcAddress failed" << endl;
    //    return 0;
    //}

    bool quit = false;
    while (!quit)
    {
        SDL_Event e;
        SDL_PollEvent(&e);
        if (e.type == SDL_QUIT)
        {
            quit = true;
        }
    }
}

The above code should be able to better reproduce the issue. After the window is launched, clicking outside the window with the mouse to change the window focus will cause the title bar, which should have been hidden, to continue displaying.

[slouken]

FYI, here is the SDL3 version of your test program:

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>

int main(int argc, char *argv[])
{
    if (!SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS)) {
        return 0;
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

    SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);

    SDL_Window *window = SDL_CreateWindow(
        "Test Window",
        800, 600,
        SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_UTILITY);

    if (!window) {
        SDL_Quit();
        return 0;
    }

    SDL_GLContext gc = SDL_GL_CreateContext(window);

    SDL_SetWindowBordered(window, false);

    SDL_SetWindowAlwaysOnTop(window, true);

    bool quit = false;
    while (!quit) {
        SDL_Event e;
        SDL_PollEvent(&e);
        if (e.type == SDL_EVENT_QUIT) {
            quit = true;
        }
    }
}

Unfortunately I'm not able to reproduce this on Windows 11. I'll try the SDL2 version, but what version of Windows are you running?

[slouken]

Oh, interesting. It does reproduce with SDL2. I'm guessing it's a difference between the functionality of SDL_WINDOW_SKIP_TASKBAR vs SDL_WINDOW_UTILITY?

Are you able to upgrade your project to SDL3?

[Majjcom]

Oh, interesting. It does reproduce with SDL2. I'm guessing it's a difference between the functionality of SDL_WINDOW_SKIP_TASKBAR vs SDL_WINDOW_UTILITY?

Are you able to upgrade your project to SDL3?

It will be a hard work.

I will try SDL_WINDOW_UTILITY to alleviate the issue.

I also found an interesting thing. If I add the WS_EX_TOOLWINDOW style to the window using SetWindowLong from the Win32 API on the previous code, the title bar will flicker after changing focus.

[vovan4ik123-engine]

FYI, here is the SDL3 version of your test program:

Thanks for your work man.