Using SubTables in repeated child windows used to work and now it doesnt

[kalebs-anotheraxiom]

Version/Branch of Dear ImGui:

Version v1.91.6 WIP, Branch: docking/stack layouts

Back-ends:

imgui_impl_XXX.cpp + imgui_impl_XXX.cpp

Compiler, OS:

Windows 11 + Unreal Engine

Full config/build information:

Dear ImGui 1.91.6 WIP (19151)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=202002
define: _WIN32
define: _WIN64
define: _MSC_VER=1938
define: _MSVC_LANG=202002
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: NULL
io.BackendRendererName: NULL
io.ConfigFlags: 0x00000081
 NavEnableKeyboard
 DockingEnable
io.ConfigViewportsNoDecoration
io.ConfigNavCaptureKeyboard
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00000000
--------------------------------
io.Fonts: 2 fonts, Flags: 0x00000000, TexSize: 1024,1024
io.DisplaySize: 2519.00,1815.00
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:
This code snippet used to work in an older version if ImGui and since updating doesn't.

Was what i was doing techincally not supposed to be possible and now the API has been corrected to make that impossible?
Or should what I'm doing still be possible

Im designing an custom items api that allows you to submit items to a Hierarchal structure and allow you to drag and drop, the api will handle all the complex table manipulation and adjusting the windows and stuff to give a convincing drag and drop experience

Screenshots/Video:

Minimal, Complete and Verifiable Example code:

                ImGui::Begin("TestingWindow");
		ImGui::BeginTable("Main Table", 1, ImGuiTableFlags_Borders);

		ImGui::TableNextColumn();
		ImGui::Text("MidText1");
		
		{
			ImGui::Begin("Sub Window");
			ImGui::BeginTable("Testing Table", 1, ImGuiTableFlags_Borders);
			ImGui::TableNextColumn();
			ImGui::Text("TestingText");
			ImGui::End();
		}
		ImGui::TableNextColumn();
		ImGui::Text("MidText2");
		{
			ImGui::Begin("Sub Window");
			ImGui::TableNextColumn();
			ImGui::Text("TestingText2");
			ImGui::EndTable();
			ImGui::End();
		}
		ImGui::TableNextColumn();
		ImGui::Text("MidText3");
		ImGui::EndTable();
		ImGui::End();

[ocornut]

Hello,

work in an older version if ImGui and since updating doesn't.

From which version?

Was what i was doing techincally not supposed to be possible and now the API has been corrected to make that impossible?

It's not 100% clear what's not working nor what you are expecting to be a "working" situation.
The screenshots seems unrelated to the provided code, and the description in the provided paragraph seems unrelated to the contents of code, so you are not making this easier.

That said, the code itself is unusual code that it is worth looking at.
AFAIK the only code that matter is:

{
    ImGui::Begin("Sub Window");
    ImGui::BeginTable("Testing Table", 1, ImGuiTableFlags_Borders);
    ImGui::TableNextColumn();
    ImGui::Text("TestingText");
    ImGui::End();
}
{
    ImGui::Begin("Sub Window");
    ImGui::TableNextColumn();
    ImGui::Text("TestingText2");
    ImGui::EndTable();
    ImGui::End();
}

Everything else seems unrelated to the issue.

First of all, out of clarity: names passed to Begin() are "absolute" in the sense that they are not derived from the ID Stack. So the first call to Begin("Sub Window") will create a window, and the second call to it will append to the already created window. But looking at the code I believe you already understood that.

1.91.3 added error recovery systems (main commit is 30c29d2) which among other things will automatically call EndTable() in End() to match the state at time of Begin() and should assert and report it as an error, is that what you are experiencing?

Indeed it is possible that this worked before but it was probably a little bit undefined behavior and prone to issues.
You could probably disable io.ConfigErrorRecovery for the whole duration of that setup, if it triggering is what's causing you problem (again, you didn't specify so I am guessing) but I honestly wouldn't recommend going that route.

It would be healthier to understand what precisely you are aiming to do so you can find alternative ways.

[kalebs-anotheraxiom]

First of all, out of clarity: names passed to Begin() are "absolute" in the sense that they are not derived from the ID Stack. So the first call to Begin("Sub Window") will create a window, and the second call to it will append to the already created window. But looking at the code I believe you already understood that.

Correct my intention is to "Append/Continue" onto the Sub window that's created because of the Table call.

Yea the screenshot isn't the best

Perhaps this is a more clear example of what I'm trying to accomplish, where the rendering goes in the order of the dotted lines

Where there's a list of items in a table, and you can select items and "Drag" them, Where there's a second "Preview" table that is pinned to your cursor.

{
    Heirarchy::Begin("Hierarchy") // Begin main table
    
    Heirarchy::BeginNode("Item 1");
    ImGui::Text("Item 1")
    Heirarchy::EndNode("Item 1");
    
    Heirarchy::BeginNode("Item 2");
    ImGui::Text("Item 2")
    Heirarchy::EndNode("Item 2");
   
    Heirarchy::BeginNode("Item 3"); // Magically jump to the drag drop preview table
    ImGui::Text("Item 3")
    Heirarchy::EndNode("Item 3"); // Magically jump back to the main table
    
    Heirarchy::BeginNode("Item 4");
    ImGui::Text("Item 4")
    Heirarchy::EndNode("Item 4");
    
    Heirarchy::BeginNode("Item 5"); // Magically jump to the drag drop preview table
    ImGui::Text("Item 5")
    Heirarchy::EndNode("Item 5") // Magically jump back to the main table
    
    Heirarchy::End() // End main table
}

Ignoring all of the complicated implementation details with the hierarchy, the main goal is to have it be possible to behind the scenes switch where the user code (The stuff between the Begin and EndNodes) renders, Ideally into an identical table but just on the cursor. In the previous version without the error recovery it was absolutely seamless

I'm not 100% certain but the last time i merged was about 9 months ago (I know i should be merging often but I'm combining docking with stack based layouts and its not so easy)

I do know for a fact that the "Error recovery" is brand new to me and I'm super glad to have it now, but is also likely what's causing the crash.

I hope i have made it more clear what I'm trying to accomplish, I don't want to get into the details of the actual system because that's not public right now. but i think I've shared enough to get the idea of what I'm doing

I think i can find a workaround by disabling the error recovery, but the main reason i opened the ticket in the first place is that old behavior that technically used to work is now causing a fatal crash. (Did you reproduce the crash from the code snippet i provided?) So i just want to bring some light to hopefully either get a definitive yes or no if what I'm doing is fundamentally flawed (Was this ever meant to be allowed, Or was there an unintentional breaking change), or to get some code added that might catch and or resolve the error