That $E_i(x, y) < 0$ indicates being inside edge only when we traverse the points in counterclockwise order, and use the normal vector of $(dY_i, -dX_i)$, rather than the other direction.
That $E_i(x, y) < 0$ indicates being inside edge only when we traverse the points in counterclockwise order, and use the normal vector of $(dY_i, -dX_i)$, rather than the other direction.