Viewport Y-offset - how to find it?

[micheus]

I need to make my own "vertex select" routine for a new plugin. So, I create some functions based on those already existent in Wings. The find_vertex converts the 3D coordinate into 2D (viewport coordinates).

The problem is that I'm always getting the Y coordinated with an offset of 75px. This is exactly the height used by title bar+menu bar+button bar by using only the default Geom window.

I couldn't find the "magic" at Wings3d code. Can someone help me?

Code:

...
    {GX,GY} = wings_wm:local2global(X, Y),
    Mode = case raw_pick(GX,GY,Vs) of
...

raw_pick(X0, Y0, Vs0) ->
    Trans = wings_u:get_matrices(0, original), % fake call for ID=0 as we force original for MM parameter
    Vs = lists:sort(find_vertex(Vs0, X0, Y0, Trans)),
    [{Vdist0,{_Xva,_Yva},_V},{_,{_Xvb,_Yvb},_}|_] = Vs,
    Vdist = math:sqrt(Vdist0),
    (Vdist =< 2.0).
find_vertex(Vs, X, Y, {_,_,{_,_,W,H}}=Trans) ->
    lists:map(fun(#vl{v=V}) ->
        {Xs,Ys} = Pos = project_vertex(V, Trans),
        io:format("  Xs,Ys (~p,~p)\n",[Xs,H-Ys]),
        Dx = X-Xs,
        Dy = Y-Ys,
        {Dx*Dx+Dy*Dy,Pos,V}
    end, Vs).