NoFocusOnAppearing on a popup makes it appear behind the parent window after clicking on a Selectable.

[quyykk]

Information:

Version: 1.84.1 (master) with 1 modification (see below)
Backend: SDL + OpenGL 3
Compiler: clang on Linux

My Issue/Question:

Using the ImGuiWindowFlags_NoFocusOnAppearing flag on a (popup) window makes it appear behind the parent window after clicking a Selectable inside that popup. I don't know whether this is a bug, or if I am missing something and I don't know enough about ImGui to tell. But since it works correctly until I click a Selectable, I believe this is a bug.

---

Background: Like many others, I'm trying to create a combo box under an InputText. To do that, I took some parts of BeginCombo and then used BeginComboPopup to create the actual popup. It works great!

Since popups take focus by default, I had to add a parameter to BeginComboPopup so that I can pass ImGuiWindowFlags_NoFocusOnAppearing to the Begin call in BeginComboPopup. And this works, until I click on a Selectable. After that, the popup renders behind the main window.

I tried to look at the code about what happens differently when passing NoFocusOnAppearing and I looked at Selectable, but I didn't see anything stand out (but I'm also a complete newcomer to ImGui so that doesn't mean anything).

Screenshot

Standalone, minimal, complete and verifiable example:

#define IMGUI_DEFINE_MATH_OPERATORS
#include "imgui_internal.h"
// Don't forget to add a ImGuiWindowFlags parameter to BeginComboPopup
// and OR it with the rest to pass them to Begin
// Or add NoFocusOnAppearing directly inside BeginComboPopup

// Add this to the example window in the main loop inside the sdl_opengl3 example.
const char *label = "test input";
static char buffer[100];
ImGuiWindow *window = ImGui::GetCurrentWindow();
ImGui::InputText(label, buffer, sizeof(buffer));
            
const auto id = ImHashStr("##combo/popup", 0, window->GetID(label));
bool isOpen = ImGui::IsPopupOpen(id, ImGuiPopupFlags_None);
if(ImGui::IsItemActive() && !isOpen)
{
    ImGui::OpenPopupEx(id, ImGuiPopupFlags_None);
    isOpen = true;
}
            
if(isOpen)
{
    const ImVec2 label_size = ImGui::CalcTextSize(label, NULL, true);
    const float w = ImGui::CalcItemWidth();
    const ImRect bb(window->DC.CursorPos,
            window->DC.CursorPos + ImVec2(w, label_size.y + GImGui->Style.FramePadding.y * 2.0f));
           
    if(ImGui::BeginComboPopup(id, bb, ImGuiComboFlags_None, ImGuiWindowFlags_NoFocusOnAppearing))
    {
        static const char *list[] = {"one", "two", "three"};
        for(int i = 0; i < 3; ++i)
                ImGui::Selectable(list[i]);
        ImGui::EndCombo();
     }
 }

[quyykk]

I fixed my issue by calling BringWindowToDisplayFront(GetCurrentWindow()); inside the BeginComboPopup if statement.

Though I still think this is a bug.

[ocornut]

Hello and sorry for my later answer.

ImGuiWindowFlags_NoFocusOnAppearing is a little bit ill-defined. It disable the call to FocusWindow() which does both bringing to display front and and bringing to focus font. I could be that current behavior is not as useful as it should be. Case in point, we use this flag once internally and we still need the window to be moved to display front.

Using the workaround is reasonable until we decide if we change that definition, but it is best to use with a IsWindowAppearing() check:

if (ImGui::IsWindowAppearing())
    ImGui::BringWindowToDisplayFront(ImGui::GetCurrentWindow());

I am currently investigating another related issue and it might contribute to evolving the design of the ImGuiWindowFlags_NoFocusOnAppearing and ImGuiWindowFlags_NoBringToFrontOnFocus flag.

[ocornut]

Linking to #718 which aims for the same end result and has lots of ideas.