Viewport-covering DockSpace capturing mouse input on viewport edge

[Bizzarrus]

Version/Branch of Dear ImGui:

Version: 1.80
Branch: docking

Back-end/Renderer/Compiler/OS

Back-ends: Custom
Compiler: MSVC
Operating System: Windows

My Issue/Question:

In our tools, we create a DockSpace that covers the whole main viewport, with the PassthruCentralNode flag. If no windows are open (and therefore, the DockSpace is empty), mouse input is passed through the dock space and to our application as expected. However, if the mouse cursor is at the very edge of the main viewport, io.WantCaptureMouse becomes true, so the mouse input is eaten by Dear ImGui and not sent to the application anymore. The Metrics/Debug window shows that it's actually a DockSpace that takes the mouse input. This behaviour is unexpected and highly confusing to our QA, as there's no visible UI that would block the mouse input from getting to the application.

So, my question is: Is this a bug, or actually expected behaviour, or are we just doing something wrong?

Screenshots/Video

(The image was taken right after clicking on the far left edge of the viewport, it was highlighting the "Dockspace/Dockspace_..." node in the metrics window as soon as I clicked. Unfortunately, my screenshot tool doesn't include the mouse cursor in the screenshot. There was no other window visible/opened other than the metrics window)

Standalone, minimal, complete and verifiable example:

static ImGuiID dockspace_id = ImGui::GetID( "GGG_Dockspace" );
static bool reset_layout = true;

ImGuiViewport* viewport = ImGui::GetMainViewport();
ImGui::SetNextWindowPos(viewport->GetWorkPos());
ImGui::SetNextWindowSize(viewport->GetWorkSize());
ImGui::SetNextWindowViewport(viewport->ID);
ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));
ImGui::Begin("Dockspace", nullptr, ImGuiWindowFlags_NoWindow | ImGuiWindowFlags_NoInputs | ImGuiWindowFlags_NoDocking);
ImGui::PopStyleVar(3);

if(reset_layout)
{
    reset_layout = false;
    ImGui::DockBuilderRemoveNode( dockspace_id );
    ImGui::DockSpace( dockspace_id, ImVec2( 0, 0 ), ImGuiDockNodeFlags_PassthruCentralNode );
    ImGui::DockBuilderSetNodeSize(dockspace_id, ImGui::GetMainViewport()->GetWorkSize());

    // Various calls to ImGui::DockBuilderSplitNode and ImGui::DockBuilderDockWindow

    ImGui::DockBuilderFinish(dockspace_id);
}
else
{
    ImGui::DockSpace( dockspace_id, ImVec2( 0, 0 ), ImGuiDockNodeFlags_PassthruCentralNode );
}

ImGui::End();

// Committing various other windows

[ocornut]

Hello, Same as #3733 This has been fixed in 1.81: https://github.com/ocornut/imgui/releases/tag/v1.81 I will update the guidelines to suggest to update to latest (even temporarily) when reporting a bug, in order to avoid this scenario of a well crafted bug report (like yours) pointing out a bug that has been fixed already. Sorry for the inconvenience!