This script-fu converts a selection (rectangular, elliptic or else) to a rectangular selection with rounded corners. The Radius is a percentage of half the selection width or height, whichever the smaller. Select Concave if you want round edges to be indented. Rounded Rectangle works by adding circles to or subtracting circles from the selection.

7.14.2.  Options

Figure 10.37.  The Rounded Rectangle dialog

Radius

With this option, you can set the radius of the corner circular design in percentage of the smallest of both width and height.

Konkav

When this option is checked rounded corners will concave (towards inside), instead of convexe (towards outside)