How is line of sight traced when the edges of a square have different terrain?

Question

Accepted Answer

Draw a line from the center of the attacker's square to the center of the target. If that line crosses an edge that blocks line of sight, such as a wall or an obscure border, the line is blocked. Only the edges the line actually crosses count.

Arydia: The Paths We Dare Tread

How is line of sight traced when the edges of a square have different terrain?