Nav crashes When Alt Clicking The Main GLFW Window

[mastergog1]

Version: Latest
Branch: docking

Back-ends: imgui_impl_GLFWcpp + imgui_impl_OPENGL.cpp
Operating System: Windows 10

The example app crashes when you interact in any way with an IMGUI window outside of the GLFW window, and then follow that interaction with an ALT + LEFT MOUSE CLICK on the GLFW window. Just move the demo window next to the glfw window, click the demo window anywhere, then alt click the glfw window.

I'm also using this branch for a work project and the same crash is happening there.

Call Stack:
->ImGui::NewFrame();
->NavUpdate()
->SetNavID(unsigned int id, int nav_layer)
-> g.NavWindow->NavLastIds[nav_layer] = id;

g.NavWindow seems to be NULL.

Same crash happens on both OpenGL examples but doesn't happen on the DirectX examples.

[ocornut]

Very interesting bug. It only happens when the first window has a menu bar and with the GLFW/SDL back-ends because:

• Pressing Alt sets up to toggle to the menu on release
• Clicking another viewport has GLFW/SDL sent an Alt key released events to the previously viewport (something which the Win32 back-ends doesn't.)
• Which in returns switches us to the menu layer and request the nav system to find an initial item to focus on. By the time the result arrives on the next frame, clicking on void has cleared focused.

Now fixed! Thanks for the bug report!

[magicfoo]

I just got a similar crash in a different context.
version: latest at this date
back-end: proprietary game engine dx11

g.NavWindow == NULL

in window->DC.NavLayerActiveMaskNext |= window->DC.NavLayerCurrentMask;
if (g.NavId == id || g.NavAnyRequest)
if (g.NavWindow->RootWindowForNav == window->RootWindowForNav)
if (window == g.NavWindow || ((window->Flags | g.NavWindow->Flags) & ImGuiWindowFlags_NavFlattened))
NavProcessItem(window, nav_bb_arg ? *nav_bb_arg : bb, id);

call stack:

• ImGui::ItemAdd() Line 6908
• ImGui::CollapseButton() Line 798
• ImGui::RenderWindowTitleBarContents() Line 5314
• ImGui::Begin("Debug##Default")
• ImGui::NewFrame()

I was hiding the unique window with a KB shortcut (i.e. it didnt enter the ImGui::Begin() of my dialog but crashes on the dummy one apparently).

[ocornut]

@magicfoo Do you remember exactly how to repro this?

I'm trying to track all code paths but haven't found a possible crash yet. (But code has changed yet, and there are asserts early on, nowadays I guess you are more likely to assert in NavUpdateAnyRequestFlag().

If this happen to you or anyone could you tell me the values of

• g.NavId
• g.NavAnyRequest
• g.NavInitRequest
• g.NavMoveScoringItems

Thanks!

[ocornut]

Found the bug!

I checked out July 10, 2020 version (~1.77) and went through every code paths and possible flow I could find.

• July 10 2020 code already had this assert already. Knowing this is really helpful.
• The only path that can set g.NavAnyRequest to true verify that g.NavWindow != NULL.
• All paths setting g.NavId != 0 are doing it where g.NavWindow != NULL (verified this several times)
• All paths which can set g.NavWindow = NULL are doing it while g.NavId != 0 (verified this several times)
• Therefore I found that if that there are paths setting g.NavWindow = NULL while there's an ongoing request and NavAnyRequest is not updated.
• Calling FocusWindow(NULL) mid-frame while there is a nav request ongoing causes the crash.

Researched this further and realized this was fixed already by 25679a4 (March 2021)
Closing!