Method CollapsingHeader

include/imgui/imgui_widgets.cpp:7267–7274

CollapsingHeader returns true when opened but do not indent nor push into the ID stack (because of the ImGuiTreeNodeFlags_NoTreePushOnOpen flag). This is basically the same as calling TreeNodeEx(label, ImGuiTreeNodeFlags_CollapsingHeader). You can remove the _NoTreePushOnOpen flag if you want behavior closer to normal TreeNode().

// CollapsingHeader returns true when opened but do not indent nor push into the ID stack (because of the ImGuiTreeNodeFlags_NoTreePushOnOpen flag).
// This is basically the same as calling TreeNodeEx(label, ImGuiTreeNodeFlags_CollapsingHeader). You can remove the _NoTreePushOnOpen flag if you want behavior closer to normal TreeNode().
bool ImGui::CollapsingHeader(const char* label, ImGuiTreeNodeFlags flags)
{
    ImGuiWindow* window = GetCurrentWindow();
    if (window->SkipItems)
        return false;
    ImGuiID id = window->GetID(label);
    return TreeNodeBehavior(id, flags | ImGuiTreeNodeFlags_CollapsingHeader, label);
}

// p_visible == NULL                        : regular collapsing header
// p_visible != NULL && *p_visible == true  : show a small close button on the corner of the header, clicking the button will set *p_visible = false