procedure Perspective(const X, Y, Z, Height, Basis: Double;
 var XP, YP: Double);
var
 Den: Double;
begin
 Den := Y + Basis;
 if Abs(Den) < 1E-100 then
 Den := 1E-100;
 XP := Basis * X / Den;
 YP := (Basis * Z + Height * Y) / Den;
end;