class Magick::RVG::Rect

def initialize(width, height, x=0, y=0)

Use the RVG::ShapeConstructors#rect method to create Rect objects in a container.
If either width or height is 0, the rectangle is not rendered.
Define a width x height rectangle. The upper-left corner is at [x, y]. 
def initialize(width, height, x=0, y=0)
    super()
    width, height, x, y = Magick::RVG.convert_to_float(width, height, x, y)
    if width < 0 || height < 0
        raise ArgumentError, "width, height must be >= 0 (#{width}, #{height} given)"
    end
    @args = [x, y, x+width, y+height]
    @primitive = :rectangle
end

def round(rx, ry=nil)

are the x- and y-axis radii. If y is omitted it defaults to x.
Specify optional rounded corners for a rectangle. The arguments 
def round(rx, ry=nil)
    rx, ry = Magick::RVG.convert_to_float(rx, ry || rx)
    if rx < 0 || ry < 0
        raise ArgumentError, "rx, ry must be >= 0 (#{rx}, #{ry} given)"
    end
    @args << rx << ry
    @primitive = :roundrectangle
    self
end