If you want to save a surface, select it and click Mask. The surface disappears and the background becomes fully visible.

The masking function helps you to leave out certain areas.. To do this, select the area and click Mask. The surface becomes completely transparent, it is possible to see the hindge completely through. For further editing, the surface is displayed with a dotted border.

example: You put a colored area over the whole facade of your house, but want to leave out a window. In this case, draw a second surface above the window and mask it. The facade remains coloured, but the window becomes visible again.