Which direction is up?

[m-zm]

In line 683 of clipper.engine.cpp, it says:

if (curr_v->pt.y > prev_v->pt.y && going_up)
{
prev_v->flags = (prev_v->flags | VertexFlags::LocalMax);
going_up = false;
}

Why is the one with the smaller y-value considered the LocalMax?

[m-zm]

ok in line 99 of clipper.engine.h, it says

///////////////////////////////////////////////////////////////////
//Important: UP and DOWN here are premised on Y-axis positive down
//displays, which is the orientation used in Clipper's development.
///////////////////////////////////////////////////////////////////

so my problem is solved.