Linux/Mac compatibility of multi-viewports

[ocornut]

This is a thread for people to discuss Linux/Mac (and notably custom window managers under Linux) specific issues with the Viewport branch, mentioned in #1542.
I am not a Linux user so I hope users will come to a solution to make the various bindings compatible with window managers.

January 2019: Viewport and Docking branches have been merged to simplify maintainance. Use the 'docking' branch to test multi-viewports.

[ocornut]

The discussions involving @Ylannl @ebachard, @s-ol, @Lecrapouille starts around here:
#1542 (comment)

[s-ol]

👍

For now I think we should focus separately on the issues with the GLFW and WM integrations I have been mostly posting about and the more subtle problems e.g. @ebachard has been seeing. I think we should focus on the latter as the GLFW stuff (window jitter) is likely a bit further from the imgui core itself and better fixed on a tangent.

I just gave the SDL demo another try on i3 and I noticed some more details, mostly related to the two ways I can interact with the windows; I can either use my WM shortcut to move and resize the windows (in my case hold the Meta key and left/right drag, lets call this WM-dragging/resizing) or I can let ImGui do it (left-drag an empty spot or titlebar, left drag window corner or edges; app-dragging/resizing).

I found the following:

• When WM-resizing I can only grow windows - dragging in the shrink-direction doesn't affect the window size at all
• When I WM-drag a window over the main viewport the drag is aborted and I have to pick the window up again to keep position it. This happens in the moment that the dragged window is contained completely inside the main viewport. When app-dragging the window the windows are not merged until the mouse is released (ideal behavior).

[Lecrapouille]

@ocornut If you want I can try to investigate concerning the segfaut I caught. I think this is not an issue concerning a particular architecture. I just call valgrind on the example_glfw_opengl3: I got:

==3237== Process terminating with default action of signal 11 (SIGSEGV)
==3237==  Access not within mapped region at address 0x0
==3237==    at 0x10B9A2: ImGui_ImplGlfw_GetWindowPos(ImGuiViewport*) (imgui_impl_glfw.cpp:477)
==3237==    by 0x128F91: ImGui::UpdateViewports() (imgui.cpp:7465)
==3237==    by 0x137431: ImGui::NewFrame() (imgui.cpp:3294)
==3237==    by 0x10B202: main (main.cpp:127)

Then I added some asserts:

static ImVec2 ImGui_ImplGlfw_GetWindowPos(ImGuiViewport* viewport)
{
    assert(NULL != viewport);
    ImGuiViewportDataGlfw* data = (ImGuiViewportDataGlfw*)viewport->PlatformUserData;
    assert(NULL != data);
    assert(NULL != data->Window);
    int x = 0, y = 0;
    glfwGetWindowPos(data->Window, &x, &y);
    return ImVec2((float)x, (float)y);
}

And I got Assertion `NULL != data' failed. I never tried rr but I'll give a try to know if it catches the bug https://rr-project.org/

[ocornut]

@Lecrapouille
What is the value of viewport->ID ?

It is calling the handler when viewport->PlatformRequestMove was set, which is set in ImGui_ImplGlfw_WindowPosCallback() when the window is moved which means the platform window was created.

There is maybe a possibility this gets called during the frame after window destruction.
Could you add printf() logging in ImGui_ImplGlfw_CreateWindow, ImGui_ImplGlfw_DestroyWindow printing viewport->ID, viewport->PlatformHandle, viewport->PlatformUserData, etc. with a frame counter?

// and the bottom of ImGui_ImplGlfw_CreateWindow
printf("[%05d] CreateWindowID %08X\n", ImGui::GetFrameCount(), viewport->ID, viewport->PlatformHandle, viewport->PlatformUserData);

// at the top of ImGui_ImplGlfw_DestroyWindow
printf("[%05d] DestroyWindow ID %08X\n", ImGui::GetFrameCount(), viewport->ID, viewport->PlatformHandle, viewport->PlatformUserData);

[Lecrapouille]

In fact to produce the segfault there is an easier way: move the "hello world" window outside (partially) the main win (else this is not working) then just move up and down your mouse cursor on the blue box of clear color to pop up/down the color panel (which starts shaking), this is enough to produce the crash.

Forget for rr I cannot use it with AMD Ryzen :( So I'm using the printf method :

In static void ImGui::UpdateViewports() inside the loop I added:

printf("ImGuiViewportP* viewport = g.Viewports[%d]; %p    %p\n", n, viewport, viewport->PlatformUserData);

Also I added printf in:

IM_DELETE(viewport);
printf("IM_DELETE(viewport) %p  %p\n", viewport, viewport->PlatformUserData);
n--;

And finally inside static ImVec2 ImGui_ImplGlfw_GetWindowPos(ImGuiViewport* viewport)

For me the NULL pointer comes from this code:

static void ImGui_ImplGlfw_DestroyWindow(ImGuiViewport* viewport) { 
...
printf("Before ImGui_ImplGlfw_DestroyWindow %p  %p\n", viewport, viewport->PlatformUserData);
    viewport->PlatformUserData = viewport->PlatformHandle = NULL;
printf("After ImGui_ImplGlfw_DestroyWindow %p  %p\n", viewport, viewport->PlatformUserData);

With valgrind + printf I see that:

--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11914810    0x11918610
Before ImGui_ImplGlfw_DestroyWindow 0x11914810  0x11918610
After ImGui_ImplGlfw_DestroyWindow 0x11914810  (nil)
ImGui_ImplGlfw_GetWindowPos 0xf635380
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11914810    (nil)
ImGui_ImplGlfw_GetWindowPos 0xf635380
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11914810    (nil)
==27446== Invalid read of size 8
==27446==    at 0x1281D3: ImGui::UpdateViewports() (imgui.cpp:7458)
==27446==    by 0x1177D4: ImGui::NewFrame() (imgui.cpp:3294)
==27446==    by 0x10AB9B: main (main.cpp:127)
==27446==  Address 0x11914838 is 40 bytes inside a block of size 224 free'd
==27446==    at 0x4C2CDDB: free (vg_replace_malloc.c:530)
==27446==    by 0x10EAD6: FreeWrapper(void*, void*) (imgui.cpp:992)
==27446==    by 0x115684: ImGui::MemFree(void*) (imgui.cpp:2815)
==27446==    by 0x145BB4: void IM_DELETE<ImGuiViewportP>(ImGuiViewportP*) (imgui.h:1428)
==27446==    by 0x1281CE: ImGui::UpdateViewports() (imgui.cpp:7457)
==27446==    by 0x1177D4: ImGui::NewFrame() (imgui.cpp:3294)
==27446==    by 0x10AB9B: main (main.cpp:127)
==27446==  Block was alloc'd at
==27446==    at 0x4C2BBAF: malloc (vg_replace_malloc.c:299)
==27446==    by 0x10EAB8: MallocWrapper(unsigned long, void*) (imgui.cpp:991)
==27446==    by 0x11562C: ImGui::MemAlloc(unsigned long) (imgui.cpp:2807)
==27446==    by 0x128720: ImGui::AddUpdateViewport(ImGuiWindow*, unsigned int, ImVec2 const&, ImVec2 const&, int) (imgui.cpp:7574)
==27446==    by 0x11F4BB: ImGui::Begin(char const*, bool*, int) (imgui.cpp:5179)
==27446==    by 0x125E59: ImGui::BeginTooltipEx(int, bool) (imgui.cpp:6890)
==27446==    by 0x1947FE: ImGui::ColorTooltip(char const*, float const*, int) (imgui_widgets.cpp:4486)
==27446==    by 0x1945CC: ImGui::ColorButton(char const*, ImVec4 const&, int, ImVec2) (imgui_widgets.cpp:4457)
==27446==    by 0x190FF1: ImGui::ColorEdit4(char const*, float*, int) (imgui_widgets.cpp:3932)
==27446==    by 0x190433: ImGui::ColorEdit3(char const*, float*, int) (imgui_widgets.cpp:3807)
==27446==    by 0x10AC42: main (main.cpp:145)
==27446== 

After some iterations we reach the assert:

ImGui_ImplGlfw_GetWindowPos 0x11a62280  (nil)
example_glfw_opengl3: ../imgui_impl_glfw.cpp:484: ImVec2 ImGui_ImplGlfw_GetWindowPos(ImGuiViewport*): Assertion `data != NULL' failed

[Lecrapouille]

@ocornut I did not see your comments when I wrote mine. I gonna try to answer you (I do not know well your code sorry)

[Lecrapouille]

note: >>> TRUE is when viewport->PlatformRequestMove = true;
1/

[00113] CreateWindowID 8C2D4FD5  (nil) (nil)
plat = data
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0x11518a60  0x1151c920
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    0x1151c920
[00129] DestroyWindow ID 8C2D4FD5 0x1151c970 0x1151c920
Before ImGui_ImplGlfw_DestroyWindow 0x11518a60  0x1151c920
After ImGui_ImplGlfw_DestroyWindow 0x11518a60  (nil)
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    (nil)
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x11518a60    (nil)
==27931== Invalid read of size 8
==27931==    at 0x12827B: ImGui::UpdateViewports() (imgui.cpp:7458)
==27931==    by 0x11787C: ImGui::NewFrame() (imgui.cpp:3294)
==27931==    by 0x10AB9B: main (main.cpp:127)
==27931==  Address 0x11518a88 is 40 bytes inside a block of size 224 free'd
==27931==    at 0x4C2CDDB: free (vg_replace_malloc.c:530)
==27931==    by 0x10EB7E: FreeWrapper(void*, void*) (imgui.cpp:992)
==27931==    by 0x11572C: ImGui::MemFree(void*) (imgui.cpp:2815)
==27931==    by 0x145C5C: void IM_DELETE<ImGuiViewportP>(ImGuiViewportP*) (imgui.h:1428)
==27931==    by 0x128276: ImGui::UpdateViewports() (imgui.cpp:7457)
==27931==    by 0x11787C: ImGui::NewFrame() (imgui.cpp:3294)
==27931==    by 0x10AB9B: main (main.cpp:127)
==27931==  Block was alloc'd at
==27931==    at 0x4C2BBAF: malloc (vg_replace_malloc.c:299)
==27931==    by 0x10EB60: MallocWrapper(unsigned long, void*) (imgui.cpp:991)
==27931==    by 0x1156D4: ImGui::MemAlloc(unsigned long) (imgui.cpp:2807)
==27931==    by 0x1287C8: ImGui::AddUpdateViewport(ImGuiWindow*, unsigned int, ImVec2 const&, ImVec2 const&, int) (imgui.cpp:7574)
==27931==    by 0x11F563: ImGui::Begin(char const*, bool*, int) (imgui.cpp:5179)
==27931==    by 0x125F01: ImGui::BeginTooltipEx(int, bool) (imgui.cpp:6890)
==27931==    by 0x1948A6: ImGui::ColorTooltip(char const*, float const*, int) (imgui_widgets.cpp:4486)
==27931==    by 0x194674: ImGui::ColorButton(char const*, ImVec4 const&, int, ImVec2) (imgui_widgets.cpp:4457)
==27931==    by 0x191099: ImGui::ColorEdit4(char const*, float*, int) (imgui_widgets.cpp:3932)
==27931==    by 0x1904DB: ImGui::ColorEdit3(char const*, float*, int) (imgui_widgets.cpp:3807)
==27931==    by 0x10AC42: main (main.cpp:145)
==27931== 
IM_DELETE(viewport) 0x11518a60  (nil)
[00131] CreateWindowID 8C2D4FD5  (nil) (nil)
plat = data
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x117832c0    0x11785450
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x117832c0  0x11785450
ImGui_ImplGlfw_GetWindowPos 0x117832c0  0x11785450
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x117832c0    0x11785450
[00133] DestroyWindow ID 8C2D4FD5 0x117854a0 0x11785450
Before ImGui_ImplGlfw_DestroyWindow 0x117832c0  0x11785450
After ImGui_ImplGlfw_DestroyWindow 0x117832c0  (nil)
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0

then several cycles after:

********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
********** ImGui_ImplGlfw_WindowPosCallback
>>> TRUE
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    0x119931b0
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x119910e0  0x119931b0
ImGui_ImplGlfw_GetWindowPos 0x119910e0  0x119931b0
[00177] DestroyWindow ID 8C2D4FD5 0x11993200 0x119931b0
Before ImGui_ImplGlfw_DestroyWindow 0x119910e0  0x119931b0
After ImGui_ImplGlfw_DestroyWindow 0x119910e0  (nil)
ImGui_ImplGlfw_GetWindowPos 0xf635380  0xf6646a0
--------------------
ImGuiViewportP* viewport = g.Viewports[0]; 0xf635380    0xf6646a0
ImGuiViewportP* viewport = g.Viewports[1]; 0x104ed210    0x10503470
ImGuiViewportP* viewport = g.Viewports[2]; 0x119910e0    (nil)
g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable 0x119910e0  (nil)
ImGui_ImplGlfw_GetWindowPos 0x119910e0  (nil)
example_glfw_opengl3: ../imgui_impl_glfw.cpp:491: ImVec2 ImGui_ImplGlfw_GetWindowPos(ImGuiViewport*): Assertion `data != NULL failed.

For me the PlatformUserData is set to NULL in ImGui_ImplGlfw_DestroyWindow then used by ImGui_ImplGlfw_GetWindowPos and not dropped by UpdateViewports inside the for (int n = 0; n < g.Viewports.Size; n++)

PPS: tried to add && viewport->PlatformUserData != NULL to if ((g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)) this does not help stopping shaking windows :(

[ebachard]

Sorry, I don't have much time these days, but I finaly found one hour, and tested the most recent code today. No time to track unfortunaly :-(

Quicly, my configuration is based on Linux Intel x86_64 (+ lot of RAM), HD 620 chipset, gcc-5.4.0 , Linux Mint 18.3 (customized 4.15.18 kernel for uvc 1.5 compatibility) / Gnome Environment
WM : default is compiz + Compton compositor + 3D effects, but I tested as well Metacity + Compton compositor, or Mutter + Compton or even Marco + Compton

What I observed:

Looks like the crash caused by the clear color window, overlaping the main SDL2 window or GLFW Window is not fixed : the crash is still there :-/

Probably a regression : using OpenGL3 + SDL2, or OpenGL3 + GLFW, whatever the WM, I see the following issue : when you drag one window outside the main window, the dragged window seems to flicker once overlaping the main window.

Other issue : when one obrder of the dragged window reaches the border of the screen, the flickering .is triggered

Maybe my imagination, but could there be a race condition between mouse coordinates and window coordinates? The simple trick to stop the ImGui Window to flicker, is to click somewhere inside the main SDL2 or GLFW window. Secondly, I remarked that the ImGui windows always tries to return at its original position, means at the point ( x ~ 50 pixels , y = 50 pixels ) from the Top Left of the main SDL or GLFW window.

Unfortunaly, I didn't make a backup of the previous sources. Got to catch with git to retrieve the old version.

Sorry, got to go. I hope I'll have more time at the end of the week.

HTH

EDIT : I wrongly wrote that the crash was fixed, but it is not in fact ...

[ebachard]

For the record, I reproduced the crash with debug enabled, and as expected, there is some null window and coordinates somewhere:

[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff00fb700 (LWP 24553)]
[New Thread 0x7fffed9c9700 (LWP 24554)]

Thread 1 "example_sdl_ope" received signal SIGSEGV, Segmentation fault.
0x0000000000403cf5 in ImGui_ImplSDL2_GetWindowPos (viewport=0x456b320) at ../imgui_impl_sdl.cpp:433
433	    SDL_GetWindowPosition(data->Window, &x, &y);
(gdb) p x
$1 = 0
(gdb) p y
$2 = 0
(gdb) p data->Window
Cannot access memory at address 0x0

To reproduce the crash :

0. compile the example_opengl3 with debug enabled ( -g option for g++ )

If you don't want to build including symbols, just comment the line starting with "DEBUG_FLAGS" (using # character )

@ocornut : in the diff below, I think I corrected a little issue in the Linux Makefile. Precisely, CXXFLAGS = (something) hides the previously defined flags.

diff --git a/examples/example_sdl_opengl3/Makefile b/examples/example_sdl_opengl3/Makefile
index 6987411..1786a67 100644
--- a/examples/example_sdl_opengl3/Makefile
+++ b/examples/example_sdl_opengl3/Makefile
@@ -20,7 +20,7 @@ SOURCES += ../imgui_impl_sdl.cpp ../imgui_impl_opengl3.cpp
 SOURCES += ../../imgui.cpp ../../imgui_demo.cpp ../../imgui_draw.cpp ../../imgui_widgets.cpp
 OBJS = $(addsuffix .o, $(basename $(notdir $(SOURCES))))
 UNAME_S := $(shell uname -s)
-
+DEBUG_FLAGS = -g
 ##---------------------------------------------------------------------
 ## OPENGL LOADER
 ##---------------------------------------------------------------------
@@ -45,8 +45,8 @@ CXXFLAGS = -I../libs/gl3w
 ifeq ($(UNAME_S), Linux) #LINUX
        ECHO_MESSAGE = "Linux"
        LIBS = -lGL -ldl `sdl2-config --libs`
-
-       CXXFLAGS = -I../ -I../../ -I../libs/gl3w `sdl2-config --cflags`
+       CXXFLAGS += ${DEBUG_FLAGS}
+       CXXFLAGS += -I../ -I../../ -I../libs/gl3w `sdl2-config --cflags`
        CXXFLAGS += -Wall -Wformat
        CFLAGS = $(CXXFLAGS)
 endif

1. run the debugger

 gdb64 --args ./example_sdl_opengl3

2. Drag the Hello window at the bottom of the main window (just put it at the border, no need to overlap)
3. click on clear color.

Expected : should open the colorpicker

4. Once the colorpicker is open, move its window to overlap the main window.

5. Then, move the mouse cursor inside the colorpicker window, exactly over "Original" color rectangle.
   Once over this area, another rectangle box opens (probably a tooltip ?)
   If the tooltip rectangle overlaps the main window, the crash occurs.
   (oppositely : it the tooltip rectangle appears inside the main window, no crash).

This crash is 100% reproductible, and I think some new windows are uninitialized, or lost their position, but I can be wrong.

Last but not least : english is not my native language, so feel free to correct me. TIA :-)

[Lecrapouille]

@ebachard You confirmed what I noticed.

I do not understand well the code but all I what I could traced is PlatformUserData is set to NULL in ImGui_ImplGlfw_DestroyWindow then used by ImGui_ImplGlfw_GetWindowPos and not dropped by UpdateViewports inside the for (int n = 0; n < g.Viewports.Size; n++) and the segfault occurs when accessing to the NULL pointer. This is what you can read in my looooong logs :)

For me is not a platform specific issue because the code is the same for all archi. I think it's most an algorithm issue or race condition between the 2 threads. But I do not understand the whole code so I cannot help more. Anyway I'm not sure this is related with flickering effects.

Did you try with valgrind ? It detects a memory corruption before the segfault occurs (which comes randomly but several cycles after). You can use rr (record & replay) which record the execution and call gdb (unfortunately I cannot use it with my Ryzen CPU).

If this can help: to trace stack, I use backward. Here the Makefile to change (also working for Darwin, never tested on Windows):

	SOURCES = backward.cpp main.cpp

	LIBS = -lGL `pkg-config --static --libs glfw3` -ldw
	CXXFLAGS += -I../ -I../../  `pkg-config --cflags glfw3` -DBACKWARD_HAS_DW=1
	CXXFLAGS += -Wall -Wformat -O2 -g -fomit-frame-pointer
	CFLAGS = $(CXXFLAGS)

You have to add in Makefile the file backward.cpp the library -ldw the define -DBACKWARD_HAS_DW=1 gcc options -O2 -g -fomit-frame-pointer and maybe to do apt-get install libdw-dev

I've truncated the bug report (after the crash) but there the stack calls (which rephrases what we wrote):

ImGui::NewFrame();
UpdateViewports();
viewport->Pos = g.PlatformIO.Platform_GetWindowPos(viewport);
glfwGetWindowPos(data->Window, &x, &y);

[Alzathar]

The following message is to report the macOS compatibility of the viewport branch using the example_glfw_opengl3binary.

• OS: macOS 10.12.6
• Hardware: MBA Late 2013
• ImGui version: 1.66 WIP (056af2b)
• GLFW version: 3.2.1 and 3.3.0

---

• Crash encountered: none

• Issue encountered:

  1. The created child viewport gains the focus and it is no more possible to move it outside of the main viewport. It is necessary to release the LMB, press it again on the child viewport to move it completely outside of the main viewport.
     

  2. When resizing a child viewport (from the bottom-right corner or the top and bottom edges), this one jumps (possible rounding error?). Note: in the following GIF, the child viewport has no problem to move outside of the main viewport because the fix proposed in the next section was applied.
     

• Possible fix

  1. No way was found with GLFW 3.2.1. However, GLFW 3.3 introduced a new window attribute that fixes this problem: GLFW_FOCUS_ON_SHOW. I tested it (see the commit Alzathar@d560773 for the modifications in example_glfw_opengl3) and the child viewport can move without problem. This code was also tested without problem under Windows 10. Unfortunately, this may introduce another problem. Indeed, as explained in the commit, the previous viewport keep the focus. Supplementary code is needed to give to the child viewport the focus when the user stops to move it and release the LMB. Is it a problem or not?
     

[ebachard]

@Alzathar : can you please confirm the crash we decribed with @Lecrapouille (the clear color one) doesn't occur on Mac OS X ?

TIA