[T-dayne]

Может быть так:

Код:

procedure TForm2.FormMouseWheel(Sender: TObject; Shift: TShiftState;
WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
var
Camera: TGLCamera;
begin
Camera:= TGLCamera.create;
Camera := GLSceneViewer1.Camera;
Camera.AdjustDistanceToTarget(Power(1.1, WheelDelta / 120));
end;