imgui_barmenu.cpp

bool ImGui::BeginBarMenu(const char* label, const bool enabled) {
    auto window = GetCurrentWindow();
    if (window->SkipItems) {
        return false;
    }
    auto& g = *GImGui;
    const auto& style = g.Style;
    const auto id = window->GetID(label);
    const char* str = "##barmenubar";
    const char* str_end = nullptr;
    IM_ASSERT(window->IDStack.Size > 1);
    const auto seed = window->IDStack.Data[window->IDStack.Size-2];
    const ImGuiID barmenubar_id = ImHash(str, str_end ? static_cast<int>(str_end - str) : 0, seed);
    if (barmenubar_id != window->IDStack.back()) {
        return false;
    }
    const auto label_size = CalcTextSize(label, nullptr, true);

    auto menu_is_open = IsPopupOpen(id);
    const auto menuset_is_open = !(window->Flags & ImGuiWindowFlags_Popup)
                                 && (g.OpenPopupStack.Size > g.CurrentPopupStack.Size
                                     && g.OpenPopupStack[g.CurrentPopupStack.Size].OpenParentId
                                     == window->IDStack.back());
    const auto backed_nav_window = g.NavWindow;
    if (menuset_is_open)
        g.NavWindow = window;
    // Odd hack to allow hovering across menus of a same menu-set (otherwise we wouldn't be able to hover parent)

    const auto pos = window->DC.CursorPos;
    // Menu inside an horizontal menu bar
    // Selectable extend their highlight by half ItemSpacing in each direction.
    // For ChildMenu, the popup position will be overwritten by the call to FindBestWindowPosForPopup() in Begin()
    const auto popup_pos = ImVec2(pos.x - style.FramePadding.x,
                                  pos.y - style.FramePadding.y + window->DC.MenuBarOffset.y + window->CalcFontSize() +
                                  GImGui->Style.FramePadding.y * 2.0f);
    window->DC.CursorPos.x += static_cast<float>(static_cast<int>(style.ItemSpacing.x * 0.5f));
    PushStyleVar(ImGuiStyleVar_ItemSpacing, style.ItemSpacing * 2.0f);
    const auto w = label_size.x;
    const auto pressed = Selectable(label, menu_is_open,
                                    ImGuiSelectableFlags_NoHoldingActiveID | ImGuiSelectableFlags_PressedOnClick |
                                    ImGuiSelectableFlags_DontClosePopups |
                                    (!enabled ? ImGuiSelectableFlags_Disabled : 0),
                                    ImVec2(w, 0.0f));
    PopStyleVar();
    window->DC.CursorPos.x += static_cast<float>(static_cast<int>(style.ItemSpacing.x * (-1.0f + 0.5f)));
    // -1 spacing to compensate the spacing added when Selectable() did a SameLine(). It would also work to call SameLine() ourselves after the PopStyleVar().

    const auto hovered = enabled && ItemHoverable(window->DC.LastItemRect, id);
    if (menuset_is_open) {
        g.NavWindow = backed_nav_window;
    }

    bool want_open = false;
    bool want_close = false;
    // Menu bar
    if (menu_is_open && pressed && menuset_is_open) {
        // Click an open menu again to close it
        want_close = true;
        want_open = menu_is_open = false;
    }
    else if (pressed || hovered && menuset_is_open && !menu_is_open) {
        // First click to open, then hover to open others
        want_open = true;
    }
    else if (g.NavId == id && g.NavMoveRequest && g.NavMoveDir == ImGuiDir_Down) {
        // Nav-Down to open
        want_open = true;
        NavMoveRequestCancel();
    }

    if (!enabled) {
        // explicitly close if an open menu becomes disabled, facilitate users code a lot in pattern such as 'if (BeginMenu("options", has_object)) { ..use object.. }'
        want_close = true;
    }
    if (!want_close && IsPopupOpen(id)) { }
    if (want_close && IsPopupOpen(id)) {
        ClosePopupToLevel(g.CurrentPopupStack.Size);
    }

    if (!menu_is_open && want_open && g.OpenPopupStack.Size > g.CurrentPopupStack.Size) {
        // Don't recycle same menu level in the same frame, first close the other menu and yield for a frame.
        OpenPopup(label);
        return false;
    }

    menu_is_open |= want_open;
    if (want_open) {
        OpenPopup(label);
    }

    if (menu_is_open) {
        // Sub-menus are ChildWindow so that mouse can be hovering across them (otherwise top-most popup menu would steal focus and not allow hovering on parent menu)
        SetNextWindowPos(popup_pos, ImGuiCond_Always);
        const auto flags = ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoMove |
                           ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoSavedSettings |
                           (window->Flags & (ImGuiWindowFlags_Popup | ImGuiWindowFlags_ChildMenu)
                                ? ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_ChildWindow
                                : ImGuiWindowFlags_ChildMenu);
        menu_is_open = BeginPopupEx(id, flags);
        // menu_is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
    }
    return menu_is_open;
}

bool ImGui::BeginBarMenuBar() {
    Spacing();
    const auto window = GetCurrentWindow();
    if (window->SkipItems) {
        return false;
    }
    window->DC.LayoutType = ImGuiLayoutType_Horizontal;
    window->DC.NavLayerCurrent++;
    window->DC.NavLayerCurrentMask <<= 1;
    BeginGroup(); // Backup position on layer 0
    PushID("##barmenubar");
    return true;
}

void ImGui::EndBarMenuBar() {
    auto window = GetCurrentWindow();
    if (window->SkipItems) {
        return;
    }
    PopID();
    EndGroup(); // Restore position on layer 0
    window->DC.LayoutType = ImGuiLayoutType_Vertical;
    window->DC.NavLayerCurrent--;
    window->DC.NavLayerCurrentMask >>= 1;
}