round_join
m_polyline.line_join(round_join);
if(m_line_join == round_join || m_line_join == bevel_join)
case round_join:
stroke->line_join(agg::round_join);
case agg::round_join:
property->AddOption(agg::round_join, "Round");
property->AddOption(agg::round_join, "Round");
return agg::round_join;