Multi Viewport: segfault when collapsing window

[gucio321]

Version/Branch of Dear ImGui:

Version c347d69, Branch: docking

Back-ends:

imgui_impl_sdl2.cpp + imgui_impl_opengl3.cpp (also happens for glfw 3.3)

Compiler, OS:

Arch Linux + g++ (GCC) 14.2.1 20240910

Full config/build information:

Dear ImGui 1.91.5 WIP (19141)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=201103
define: __linux__
define: __GNUC__=14
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_sdl2
io.BackendRendererName: imgui_impl_opengl3
io.ConfigFlags: 0x00000483
 NavEnableKeyboard
 NavEnableGamepad
 DockingEnable
 ViewportsEnable
io.ConfigViewportsNoDecoration
io.ConfigNavCaptureKeyboard
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C0E
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasVtxOffset
 RendererHasViewports
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 1280.00,720.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,3.00
style.FrameRounding: 0.00
style.FrameBorderSize: 0.00
style.ItemSpacing: 8.00,4.00
style.ItemInnerSpacing: 4.00,4.00

Details:

My Issue/Question:

While working on cimgui-go I noticed that double-clicking window titlebar, when it is 'detached' from the main viewport crashes an app with segfault.

Segmentation fault (core dumped)

(gdb) bt
#0  0x00007ffff655914d in ?? () from /usr/lib/libGLX_nvidia.so.0
#1  0x00007ffff4cb3c13 in ?? () from /usr/lib/libnvidia-glcore.so.565.57.01
#2  0x00007ffff657a15e in ?? () from /usr/lib/libGLX_nvidia.so.0
#3  0x00007ffff6548490 in ?? () from /usr/lib/libGLX_nvidia.so.0
#4  0x00007ffff7e2be6a in X11_GL_SwapWindow (_this=<optimized out>, window=<optimized out>)
    at /usr/src/debug/sdl2/SDL2-2.30.9/src/video/x11/SDL_x11opengl.c:1010
#5  0x0000555555669fe8 in ImGui_ImplSDL2_SwapBuffers (viewport=0x5555557631a0) at ../../backends/imgui_impl_sdl2.cpp:1142
#6  0x00005555555948d7 in ImGui::RenderPlatformWindowsDefault (platform_render_arg=0x0, renderer_render_arg=0x0) at ../../imgui.cpp:16478
#7  0x0000555555559f1a in main () at main.cpp:218

Screenshots/Video:

Screencast.From.2024-11-06.10-42-38.mp4

Minimal, Complete and Verifiable Example code:

examples/example_sdl2_opengl3

[AMRD1234]

i have the same issue with imgui docking...
on windows docking is working well but i dont know why this is so buggy in linux (im using ubuntu).
when i put the imgui demo window or any window outside of GLFW MAIN Window it getts too buggy....
ocornut does this issue solvable???

[ocornut]

@gucio321 You would likely need to investigate this further on your end.

Some thoughts:

• I cannot understand how collapsing would make a difference from the point of view of rendering. It's just a smaller window. It would call SDL_SetWindowSize() first (and GLFW equivalent), and immediately attempt to render and swap.

Some pointers:

• Try updating/toying with your OpenGL drivers and setups. They are known to be a mess.
• Try to confirm first that it happens with unmodified examples app.
• Try with the equivalent SDL3 example.
• Try to comment out all or some of the code in ImGui_ImplOpenGL3_RenderWindow() and see if it makes a difference. AKA see if simply calling the SDL sides of things, aka SDL_SetWindowSize() then ImGui_ImplSDL2_SwapBuffers() makes a difference.
• Just in case, try testing for the return value of the SDL_GL_MakeCurrent() calls in ImGui_ImplSDL2_RenderWindow() and ImGui_ImplSDL2_SwapBuffers(). You can use IM_ASSERT(ret_value == 0);.

For all those attempts, please be explicit what you have you tried and the results. Details would be useful.

[gucio321]

Try updating/toying with your OpenGL drivers and setups. They are known to be a mess.

I use arch btw 😄

Try to confirm first that it happens with unmodified examples app.

Yes, I'm on latest docking release (not modified)

Try with the equivalent SDL3 example.

same.

I cannot understand how collapsing would make a difference from the point of view of rendering. It's just a smaller window. It would call SDL_SetWindowSize() first (and GLFW equivalent), and immediately attempt to render and swap.

I've just tested for a while and dtected an interesting behavior: The easiest way to reproduce this crash is collapsing but also, fast resizing the window causes that (If I do that slowly, it doesn't happen 😄).

I'll test to play a little bit more later

[gucio321]

@ocornut I did another test: I boted up my fedora and tested there.
On Gnome it crashes just like on my arch.
But when I choose gnome on Xorg, it works fine.
I think that since SDL/GLFW does not support Multi Viewport on wayland, it automatically defaults to Xorg so XWayland. And this is a problem for some reason...