Fix issue #96

[maritim]

Fix #96.

I encountered the same problem as @SaltyLeung . According to the behavior I understand, void SetRect(float x, float y, float width, float height) should set a rectangle on the screen in which to draw the control elements. It can be understood that outside the specified rectangle, drawing should not be allowed. However, the control elements are also drawn outside.

I solved this problem as recommended.