Method BeginListBox

include/imgui/imgui_widgets.cpp:8782–8822

This is essentially a thin wrapper to using BeginChild/EndChild with the ImGuiChildFlags_FrameStyle flag for stylistic changes + displaying a label. This handle some subtleties with capturing info from the label. If you don't need a label you can pretty much directly use ImGui::BeginChild() with ImGuiChildFlags_FrameStyle. Tip: To have a list filling the entire window width, use size.x = -FLT_MIN

// Tip: To have a list filling the entire window width, use size.x = -FLT_MIN and pass an non-visible label e.g. "##empty"
// Tip: If your vertical size is calculated from an item count (e.g. 10 * item_height) consider adding a fractional part to facilitate seeing scrolling boundaries (e.g. 10.5f * item_height).
bool ImGui::BeginListBox(const char* label, const ImVec2& size_arg)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindow* window = GetCurrentWindow();
    if (window->SkipItems)
        return false;

    const ImGuiStyle& style = g.Style;
    const ImGuiID id = GetID(label);
    const char* label_end = FindRenderedTextEnd(label);
    const ImVec2 label_size = CalcTextSize(label, label_end, false);

    // Size default to hold ~7.25 items.
    // Fractional number of items helps seeing that we can scroll down/up without looking at scrollbar.
    ImVec2 size = ImTrunc(CalcItemSize(size_arg, CalcItemWidth(), GetTextLineHeightWithSpacing() * 7.25f + style.FramePadding.y * 2.0f));
    ImVec2 frame_size = ImVec2(size.x, ImMax(size.y, label_size.y));
    ImRect frame_bb(window->DC.CursorPos, window->DC.CursorPos + frame_size);
    ImRect bb(frame_bb.Min, frame_bb.Max + ImVec2(label_size.x > 0.0f ? style.ItemInnerSpacing.x + label_size.x : 0.0f, 0.0f));
    g.NextItemData.ClearFlags();

    if (!IsRectVisible(bb.Min, bb.Max))
    {
        ItemSize(bb.GetSize(), style.FramePadding.y);
        ItemAdd(bb, 0, &frame_bb);
        g.NextWindowData.ClearFlags(); // We behave like Begin() and need to consume those values
        return false;
    }

    // FIXME-OPT: We could omit the BeginGroup() if label_size.x == 0.0f but would need to omit the EndGroup() as well.
    BeginGroup();
    if (label_size.x > 0.0f)
    {
        ImVec2 label_pos = ImVec2(frame_bb.Max.x + style.ItemInnerSpacing.x, frame_bb.Min.y + style.FramePadding.y);
        RenderText(label_pos, label, label_end, false);
        window->DC.CursorMaxPos = ImMax(window->DC.CursorMaxPos, label_pos + label_size);
        AlignTextToFramePadding();
    }

    BeginChild(id, frame_bb.GetSize(), ImGuiChildFlags_FrameStyle);
    return true;
}

void ImGui::EndListBox()
{