Multiple Contexts don't work as expected

[Thalhammer]

Describe the bug Maybe I am not using it correctly, but it looks like creating multiple contexts is broken. From what I found the reason for this is that void Initialize(ImNodesContext* context) sets GImNodes->EditorCtx to GImNodes->DefaultEditorCtx even if the newly created context is not the current global context. This is causing a crash once you attempt to use the newly created context, because context->EditorCtx is null. https://github.com/Nelarius/imnodes/blob/master/imnodes.cpp#L1633 The fix for this should be simple:

• Either have CreateContext save the current global, set the new context as the global and restore it after calling initialize, or
• Remove EditorContextSet (since its not used anywhere else anyway) and directly assign context->EditorCtx = context->DefaultEditorCtx

How To Reproduce

auto global = ImNodes::CreateContext(); // Creates global context
auto ctx = ImNodes::CreateContext(); // New context
ImNodes::SetCurrentContext(ctx);
// Do any operation here => Crash as soon as it touches GImNodes->EditorCtx

Expected behavior global and ctx represent two distinct contexts, each of which can be used for rendering and does not influence each other or leak memory.

Desktop:

• OS: elementary OS 5.1.7 Hera (Linux 5.4.0-96-generic)
• Compiler: Ubuntu clang version 12.0.1-++20211102090516+fed41342a82f-1~exp1~20211102211019.11
• Version: e563371cee49eb42da08cca1e0209d30d452c665

[Thalhammer]

Found out you're supposed to use CreateEditorContext for this use case, however I still think that given the functions for multiple contexts exists it should work correctly.

[Nelarius]

Hi @Thalhammer ! Glad you were able to figure it out.

You raised an interesting issue. There's two kinds of state behind the scenes:

• state which gets rebuilt every frame. That's contained in ImNodesContext. It also contains a pointer to the current ImNodesEditorContext.
• state which gets retained between the frames, such as the positions of the nodes. This is the job of ImNodesEditorContext.

I suppose there is no reason why we couldn't just have a single ImNodesContext which would contain everything we need. It might be easier for someone who is trying to use the library solely based on reading imnodes.h.

I will keep this open issue open, as this is something to consider before making the API final.