Tying out shortcuts + auto focus items for a ImGui widget.

imgui_customnav_test.cpp

// code for: https://x.com/amu_mhr/status/2006940064711053355?s=20

extern int ImFormatString(char* buf, size_t buf_size, const char* fmt, ...);

// dubious function to focus `InputText` widgets with nav cursor, this avoid having to press enter to edit them
// NOTE: `ImGui::Shortcut` handles focusing but not sure how to replicate that when using arrow keys (i.e no shortcut just navigation)
//       This has a downside that items to the left/right of the input box cannot be reached using arrow keys (only up/down nav will work!)
auto AutoFocusNextItem = [](const char* item_label)
    {
        const ImGuiID item_id = ImGui::GetCurrentWindow()->GetID(item_label);
        ImGui::PushID(item_id);

        const ImGuiID StorageId = ImGui::GetCurrentWindow()->GetID("AutoActivate");
        const bool had_focus = ImGui::GetStateStorage()->GetBool(StorageId);
        const bool has_focus = (ImGui::GetFocusID() == item_id);

        if (has_focus && !had_focus)
        {
            ImGui::SetKeyboardFocusHere();
        }

        ImGui::GetStateStorage()->SetBool(StorageId, has_focus);
        ImGui::PopID();
    };

if (ImGui::Begin("Test"))
{
    // keep track of childb focus state in order to register shortcuts
    static bool childb_has_focus = false;
    static int childb_last_focused_item = -1;

    if (ImGui::BeginChild("ChildA", ImVec2(0, 0), ImGuiChildFlags_FrameStyle | ImGuiChildFlags_NavFlattened | ImGuiChildFlags_AutoResizeY))
    {
        static char buff0[64], buff1[64];

        if (childb_has_focus) //shortcut mapping
        {
            ImGui::SetNextItemShortcut(ImGuiKey_Tab, ImGuiInputFlags_Repeat);
        }
        AutoFocusNextItem("Text0");
        ImGui::InputText("Text0", buff0, sizeof(buff0));

        if (childb_has_focus && childb_last_focused_item == 0) //shortcut mapping
        {
            ImGui::SetNextItemShortcut(ImGuiKey_UpArrow, ImGuiInputFlags_Repeat);
        }
        AutoFocusNextItem("Text1");
        ImGui::InputText("Text1", buff1, sizeof(buff1));
    }
    ImGui::EndChild();

    if (ImGui::BeginChild("ChildB", ImVec2(0,0), ImGuiChildFlags_FrameStyle))
    {
        childb_has_focus = ImGui::IsWindowFocused();

        // auto activate the window once it has has nav cursor (don't have to press enter to focus)
        // this however draws the child window nav cursor for one frame, appears as a flicker :(
        const bool had_nav_focus = childb_has_focus;
        const bool has_nav_focus = (ImGui::GetCurrentContext()->NavId == ImGui::GetCurrentWindow()->ChildId);
        const bool trigger_auto_activate = has_nav_focus && !had_nav_focus;
        if (trigger_auto_activate && childb_last_focused_item == -1)
        {
            // make sure to select the first item as we don't have flattened nav which automatically handles this.
            childb_last_focused_item = 0;
        }
        
        for (int i = 0; i < 64; ++i)
        {
            char labelBuff[32];
            ImFormatString(labelBuff, sizeof(labelBuff), "Item %i", i);
            if (trigger_auto_activate && (childb_last_focused_item == i))
            {
                ImGui::SetKeyboardFocusHere();
            }
            if (ImGui::Selectable(labelBuff, childb_last_focused_item == i)) { /* do something */ }
            if (ImGui::IsItemFocused())
            {
                childb_last_focused_item = i;
            }
        }
    }
    ImGui::EndChild();
}
ImGui::End();