SDL_GetWindowBordersSize() returns wrong values after returning from fullscreen

[SRSaunders]

When I call SDL_GetWindowBordersSize() after RBDoom3BFG initializes, I get expected values returned for the XFCE window manager on Manjaro Linux: topBorder=28, leftBorder=2, bottomBorder=2, rightBorder=2.

However, if I fullscreen the game window (either programatically or via the window manager) and then return to windowed mode, the same call then returns incorrect values: topBorder=28, leftBorder=0, bottomBorder=0, rightBorder=0. This is not a timing issue as the same call will return the same incorrect values long after the window has returned to windowed mode (e.g. just before fullscreening again).

However, if I call SDL_SetWindowPosition( window, windowPosX, windowPosY ) before returning to windowed mode via SDL_SetWindowFullscreen( window, SDL_FALSE ) and SDL_RestoreWindow( window ), then SDL_GetWindowBordersSize() does return the correct values of topBorder=28, leftBorder=2, bottomBorder=2, rightBorder=2.

This is different than native SDL2 which did not require setting the window position before returning to windowed mode. Is this expected behaviour for SDL_GetWindowBordersSize()? Or is it a bug?

[Kontrabant]

Does this occur on all window managers, or just XFCE? Odd that the top would be correct, and the sides wrong.

I tried logging the values received when the _NET_FRAME_EXTENTS event occurs on XFCE, but with my testing, the numbers are always correct on SDL3 and sdl2-compat (29,2,2,2 in windowed, all zero while fullscreen, and returning to 29,2,2,2 when leaving fullscreen). The only time I see a non-zero value for the top with the sides and bottom as zero is when the window is maximized.

[SRSaunders]

@Kontrabant I have instrumented my SDL calls and events received. Here is what I am seeing:

When SDL_SetWindowPosition() is called after restoring from fullscreen:

SDL_MaximizeWindow() before fullscreen mode
SDL_SetWindowFullscreen(SDL_WINDOW_FULLSCREEN) for fullscreen mode

SDL_WINDOWEVENT_MOVED = 0, 0

SDL_WINDOWEVENT_RESIZED = 2560, 1440

SDL_GetWindowBordersSize (before restore) = 28, 0, 0, 0
SDL_WINDOW_FULLSCREEN detected -> SDL_SetWindowFullscreen(FALSE) for windowed mode
SDL_WINDOW_MAXIMIZED detected -> SDL_RestoreWindow() for windowed mode
SDL_GetWindowPosition (after restore) = 892, 82
SDL_GetWindowBordersSize (after restore) = 28, 0, 0, 0
SDL_SetWindowBordered(SDL_TRUE) (after restore)
SDL_GetWindowBordersSize (after restore) = 28, 0, 0, 0
SDL_SetWindowSize (after restore) = 1639, 915
SDL_GetWindowSize (after restore) = 1639, 915
SDL_SetWindowPosition (after restore) = 892, 82
SDL_GetWindowPosition (after restore) = 892, 82

SDL_WINDOWEVENT_RESIZED = 1639, 915

SDL_WINDOWEVENT_MOVED = 894, 82

However, when SDL_SetWindowPosition() is called before restoring from fullscreen:

SDL_MaximizeWindow() before fullscreen mode
SDL_SetWindowFullscreen(SDL_WINDOW_FULLSCREEN) for fullscreen mode

SDL_WINDOWEVENT_MOVED = 0, 0

SDL_WINDOWEVENT_RESIZED = 2560, 1440

SDL_SetWindowPosition (before restore) = 892, 82
SDL_GetWindowPosition (before restore) = 0, 0
SDL_GetWindowBordersSize (before restore) = 28, 2, 2, 2
SDL_WINDOW_FULLSCREEN detected -> SDL_SetWindowFullscreen(FALSE) for windowed mode
SDL_GetWindowPosition (after restore) = 892, 82
SDL_GetWindowBordersSize (after restore) = 28, 2, 2, 2
SDL_SetWindowBordered(SDL_TRUE) (after restore)
SDL_GetWindowBordersSize (after restore) = 28, 2, 2, 2
SDL_SetWindowSize (after restore) = 1639, 915
SDL_GetWindowSize (after restore) = 1639, 915

SDL_WINDOWEVENT_MOVED = 892, 82

SDL_WINDOWEVENT_RESIZED = 1639, 915

Some things I notice:

1. When calling SDL_SetWindowPosition() after restoring from fullscreen, the border sizes look wrong and I get window position creep (i.e. the window moved event is not quite the same as the window position set).
2. When calling SDL_SetWindowPosition() with non-zero values before restoring from fullscreen, the borders look correct, there is no position creep, and it appears the window is automatically moved out of MAXIMIZED state prior to me clearing the FULLSCREEN mode.

[slouken]

Can you provide a minimal test along with steps that shows the issue? That will help us when investigating and verifying any fixes.

Thanks!