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Bug 4332

Summary: SDL_WINDOW_FULLSCREEN window disappears upon first call to SDL_PumpEvents, workaround provided
Product: SDL Reporter: Elmar <elmar>
Component: eventsAssignee: Ryan C. Gordon <icculus>
Status: ASSIGNED --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2    
Version: 2.0.9   
Hardware: x86_64   
OS: Linux   

Description Elmar 2018-10-26 07:35:57 UTC 
Dear all,

I'm migrating my app from SDL1 to SDL2. Using the latest 2.0.9 nightly snapshot, my app disappears as soon as it goes fullscreen, this happens in CentOS 6 (KDE), CentOS 7 (KDE) and Ubuntu 18.04 (default desktop), while Windows and MacOS are fine.

After a lot of debugging, I found the following:
Having created the fullscreen window, upon calling SDL_PumpEvents, the function X11_DispatchEvent receives a FocusOut event. It calls X11_DispatchFocusOut, which calls SDL_SetKeyboardFocus(NULL), which calls SDL_SendWindowEvent(SDL_WINDOWEVENT_FOCUS_LOST), which calls  SDL_OnWindowFocusLost(window), which checks ShouldMinimizeOnFocusLoss and finally calls SDL_MinimizeWindow(window) - and my app is gone.

The "workaround" is to fudge ShouldMinimizeOnFocusLoss with
SDL_SetHint(SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS,"0");

Obviously, there are zillions of SDL2 Linux apps that use fullscreen happily, so the issue must somehow be caused by my app. Unfortunately I didn't have the time to investigate why the X-server sends a nasty FocusOut event in the first place,  but maybe this story rings a bell for some of you.

This could be a duplicate of this old bug report:
https://bugzilla.libsdl.org/show_bug.cgi?id=2642

Best regards,
Elmar
Comment 1 Sam Lantinga 2018-10-28 21:18:51 UTC 
Ryan, can you look to see if this is a regression in SDL 2.0.9?

Thanks!
Comment 2 Elmar 2018-10-28 22:14:36 UTC 
(In reply to Sam Lantinga from comment #1)
> Ryan, can you look to see if this is a regression in SDL 2.0.9?
> 
> Thanks!

I initially had the problem with SDL 2.0.8, and then updated to the latest 2.0.9 devsnapshot to check that it's still there before filing this report.
Comment 3 Ryan C. Gordon 2018-10-28 23:28:34 UTC 
Checking tonight.

—ryan.
Comment 4 Ryan C. Gordon 2018-10-30 04:03:57 UTC 

This isn’t reproducing for me; is your source code available somewhere that I can see (even if it’s just the piece that creates the window and pumps events)?

Or even a very small example C program that just creates a window and triggers this bug?

--ryan.

I’m
Comment 5 Elmar 2018-10-30 07:35:32 UTC 
Getting a small example program will be many hours of work. But since you guys are doing such a great job, I spent the first hour to get closer to the source of the problem.

I found the following:

- Create Window:
vga_window=SDL_CreateWindow("MyTitle",0,0,1280,1024,0x2007);

- Create OpenGL context with shader initialization etc.

- SDL_PumpEvents();

- for (i=0;i<10;i++) SDL_GL_SwapWindow(vga_window);

- SDL_PumpEvents();

The above recipe works fine. BUT if I delete the first SDL_PumpEvents, the window disappears.

Conclusion: I have to call SDL_PumpEvents *before* the first call to SDL_GL_SwapWindow.

This is reproducible on three different Linux PCs, two with NVIDIA proprietary drivers, one with AMD fglrx driver.

Does this help?

Best regards,
Elmar