rounded-rectangle in dc-path%

Closes the open sub-path, if any, and adds a closed path that represents a round-cornered rectangle whose top-left corner is (x,y) and whose dimensions are width by height. (This convenience method is implemented in terms of close, move-to, arc, and line-to.)

A path is not connected to any particular dc<%> object, so setting a dc<%> origin or scale does not affect path operations. Instead, a dc<%>'s origin and scale apply at the time that the path is drawn or used to set a region.

• (send a-dc-path rounded-rectangle x y width height radius) -> void
     x : real number
     y : real number
     width : non-negative real number
     height : non-negative real number
     radius = -0.25 : real number

  If radius is positive, the value is used as the radius of the rounded corner. If radius is negative, the absolute value is used as the the proportion of the smallest dimension of the rectangle.

  If radius is less than -0.5 or more than half of width or height, an exn:fail:contract exception is raised.