Reset ImGui::GetIO().BackendFlags on shutdown

[GereonV]

Relevant code in ImGui_ImplOpenGL3_Init():

#ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_VTX_OFFSET
if (bd->GlVersion >= 320)
    io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.
#endif

(Note: can always be reset, regardless of whether it was actually set on initialization)

---

Relevant code in ImGui_ImplGlfw_Init():

io.BackendFlags |= ImGuiBackendFlags_HasMouseCursors;         // We can honor GetMouseCursor() values (optional)
io.BackendFlags |= ImGuiBackendFlags_HasSetMousePos;          // We can honor io.WantSetMousePos requests (optional, rarely used)

[ocornut]

Hello,
I assume your use case is you are switching backends while a same imgui context is being reused? Which backends are you using? That code should be applied to every backends.

[GereonV]

Hi,
although I didn't check you're probably right and most backends need a change like this. I realized this issue when I read through backends/imgui_impl_glfw.cpp on my quest to understand how the library works as a whole. I thought of the time I used the same ImGui context for GLFW and SDL. I realized this could be a problem when switching backends in general. I later read backends/imgui_impl_opengl3.cpp and found the same thing. I only checked these, because they're the backends I currently use. I can check the other backends for io.BackendFlags (shouldn't be hard) and add the reset there as well. This is my very first PR (except for the other one I opened 20 mins prior to this one) so I don't know whether it's normal to ask: can I add these changes?
PS: excuse me for not being concise 😅

[ocornut]

Hello,

I think the changes are fine and correct but:

• they would need to be applied to all backends.
• multiple clear can be done together, e.g.

io.BackendFlags &= ~ImGuiBackendFlags_HasMouseCursors;
io.BackendFlags &= ~ImGuiBackendFlags_HasSetMousePos;

Can be:

io.BackendFlags &= ~(ImGuiBackendFlags_HasMouseCursors | ImGuiBackendFlags_HasSetMousePos);

• And ultimately this needs to be completed with a second commit on the docking branch.

As this is relatively easy I don't mind doing it on my side, but if you are interested in pushing this to make a neat PR be my guest :)

[GereonV]

@ocornut I'm done. The branch name obviously isn't accurate anymore, because all backends that set io.BackendFlags while initializing have been adjusted and not just GLFW and OpenGL3.

I commited the changes for Metal and OSX separately because I wanted to comment on it in the commit message: it also IM_ASSERTs that the backend has been initialized and resets io.Backend*UserData and io.Backend*Name to nullptr in addition to clearing the bits of io.BackendFlags.

[ocornut]

Merged as 055e715
I have folded #6335 into the same, added the missing clear for ImGuiBackendFlags_HasGamepad in the 5 platform backends (if you grep for BackendFlags in backends/ folder you would find every use) and minor aesthetic tweaks.
Thank you!

[GereonV]

I am happy to have contributed ^^

[ocornut]

Also pushed 1f2b84a with equivalent flag clear for docking branch.