Each country has a fixed labor pool split between cloth and wine. Its production-possibility frontier (PPF) is the straight line joining "all cloth" to "all wine" on the shared diagram at right — its own rate for each good sets how far that line reaches on each axis.
A country's opportunity cost of cloth is how much wine it must give up to make one more unit of cloth — the slope of its own PPF (wine rate ÷ cloth rate). Comparative advantage in cloth belongs to whichever country's opportunity cost of cloth is lower — this has nothing to do with which country is more productive in absolute terms.
Drag Specialization to move each country's labor away from a 50/50 split toward full specialization in its own comparative-advantage good. Drag Trade amount to exchange cloth for wine between the two countries at a price midway between their two opportunity costs. The green consumption dot can land outside a country's own frontier — more of both goods than that country could ever produce alone.
opportunity cost of cloth = wine_rate / cloth_rate
comparative advantage in cloth → lower opportunity cost of cloth
trade price p, between the two countries' opportunity costs
consumption = own production ± traded quantity, valued at p