Function dew is similar to vect but use drops instead of arrows.
MGL code:
call 'prepare2v' subplot 1 1 0 '':title 'Dew plot':light on:box:dew a b
C++ code:
void smgl_dew(mglGraph *gr)
{
mglData a,b; mgls_prepare2v(&a,&b);
if(big!=3) {gr->SubPlot(1,1,0,""); gr->Title("Dew plot");}
gr->Box(); gr->Light(true); gr->Dew(a,b);
}