Function TabBarCalcScrollableWidth

src/external/imgui/imgui_widgets.cpp:7934–7937

Scrolling happens only in the central section (leading/trailing sections are not scrolling)

// Scrolling happens only in the central section (leading/trailing sections are not scrolling)
static float TabBarCalcScrollableWidth(ImGuiTabBar* tab_bar, ImGuiTabBarSection* sections)
{
    return tab_bar->BarRect.GetWidth() - sections[0].Width - sections[2].Width - sections[1].Spacing;
}

// This is called only once a frame before by the first call to ItemTab()
// The reason we're not calling it in BeginTabBar() is to leave a chance to the user to call the SetTabItemClosed() functions.