Allow Splitting same node multiple times

[MegaMech]

This allows splitting a dock node so that you can create a left/right/up/down docking location programmatically.

Without this, the programmer can only split one direction off of the main dockId which prevents docking multiple windows to the other sides of the main program window.

According to other issues regarding docking, this appears to be intended functionality.

Example:

    const ImGuiID dockId = ImGui::GetID("main_dock");
    if (!ImGui::DockBuilderGetNode(dockId)) {
        ImGui::DockBuilderRemoveNode(dockId);
        ImGui::DockBuilderAddNode(dockId, ImGuiDockNodeFlags_NoTabBar);

        ImGui::DockBuilderDockWindow("Main Game", dockId);

        ImGuiID rightId = ImGui::DockBuilderSplitNode(dockId, ImGuiDir_Right, 0.25f, nullptr, nullptr);
        ImGuiID topId = ImGui::DockBuilderSplitNode(dockId, ImGuiDir_Up, 0.25f, nullptr, nullptr);
        ImGuiID bottomId = ImGui::DockBuilderSplitNode(dockId, ImGuiDir_Down, 0.25f, nullptr, nullptr);
        ImGui::DockBuilderSetNodeSize(rightId, ImVec2(viewport->Size.x * 0.2f, viewport->Size.y));
        ImGui::DockBuilderSetNodeSize(topId, ImVec2(viewport->Size.x, viewport->Size.y * 0.1f));
        ImGui::DockBuilderSetNodeSize(bottomId, ImVec2(viewport->Size.x, viewport->Size.y * 0.1f));
        
        ImGui::DockBuilderDockWindow("Scene Explorer", rightId);
        ImGui::DockBuilderDockWindow("Tools", topId);
        ImGui::DockBuilderDockWindow("Content Browser", bottomId);

        ImGui::DockBuilderFinish(dockId);
    }

    ImGui::DockSpace(dockId, ImVec2(0.0f, 0.0f), ImGuiDockNodeFlags_None | ImGuiDockNodeFlags_NoDockingInCentralNode);

[ocornut]

Thank you for the PR and the code snippet (which is very useful).

Before all, you'll want to call ImGui::DockBuilderSetNodeSize(dockId, ImVec2(viewport->Size.x, viewport->Size.y)); right after creating it if you want the subsequent split to correctly reflect given ratios.

It's a little confusing and hard to comprehend even for me as those API haven't been touched for a long time and are not ideal, but what you are doing was not possible at the time I published docking. Effectively now it does, probably because the underlying DockNodeTreeSplit() handles moving things better. I agree it can make use of DockBuilder API a little easier as effectively the building code doesn't have to maintain as many identifiers.

FYI the intent was to build the hierarchy:

ImGuiID topBottomId;
ImGuiID topId = ImGui::DockBuilderSplitNode(dockId, ImGuiDir_Up, 0.25f, nullptr, &topBottomId);

ImGuiID bottomId;
ImGuiID midId;
ImGui::DockBuilderSplitNode(topBottomId, ImGuiDir_Down, 0.25f, &bottomId, &midId);

ImGuiID leftId;
ImGuiID rightId;
ImGui::DockBuilderSplitNode(midId, ImGuiDir_Right, 0.25f, &rightId, &leftId);

ImGui::DockBuilderDockWindow("Main Game", leftId);
ImGui::DockBuilderDockWindow("Scene Explorer", rightId);
ImGui::DockBuilderDockWindow("Tools", topId);
ImGui::DockBuilderDockWindow("Content Browser", bottomId);

Notice how the splits are done in the opposite order, and it is also more verbose and more confusing.

I would need to study the code a little more to confirm that this isn't losing state.

[ocornut]

Merged as bb8d295, thank you.