require 'cairo'

format = Cairo::FORMAT_ARGB32
width = 300
height = 200
radius = height / 3 # 半径

# surface = Cairo::ImageSurface.new(format, width, height)
surface = Cairo::SVGSurface.new("japan6.svg", width, height)
context = Cairo::Context.new(surface)

# 背景と枠
context.set_source_rgb(1, 1, 1) # 白
context.rectangle(0, 0, width, height)
context.fill
context.set_source_rgb(0.5,0.5,0.5) # 灰
context.rectangle(0, 0, width, height)
context.stroke

# 赤丸
context.set_source_rgb(1, 0, 0) # 赤
context.arc(width / 2, height / 2, radius, 0, 2 * Math::PI)
context.fill

surface.write_to_png("japan6.png")