Method Begin

lib/imgui/imgui.cpp:2191–2208

Use case A: Begin() called from constructor with items_height<0, then called again from Sync() in StepNo 1 Use case B: Begin() called from constructor with items_height>0 FIXME-LEGACY: Ideally we should remove the Begin/End functions but they are part of the legacy API we still support. This is why some of the code in Step() calling Begin() and reassign some fields, spaghetti style.

// Use case B: Begin() called from constructor with items_height>0
// FIXME-LEGACY: Ideally we should remove the Begin/End functions but they are part of the legacy API we still support. This is why some of the code in Step() calling Begin() and reassign some fields, spaghetti style.
void ImGuiListClipper::Begin(int count, float items_height)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindow* window = g.CurrentWindow;

    StartPosY = window->DC.CursorPos.y;
    ItemsHeight = items_height;
    ItemsCount = count;
    StepNo = 0;
    DisplayEnd = DisplayStart = -1;
    if (ItemsHeight > 0.0f)
    {
        ImGui::CalcListClipping(ItemsCount, ItemsHeight, &DisplayStart, &DisplayEnd); // calculate how many to clip/display
        if (DisplayStart > 0)
            SetCursorPosYAndSetupDummyPrevLine(StartPosY + DisplayStart * ItemsHeight, ItemsHeight); // advance cursor
        StepNo = 2;
    }
}

void ImGuiListClipper::End()
{