# arc.rb

    #!/usr/local/bin/ruby18 -w
    require 'RMagick'

    i = Magick::Image.new(300, 220, Magick::HatchFill.new("white","lightcyan2"))
    gc = Magick::Draw.new

    # Draw the border rectangle.
    gc.fill_opacity(0)
    gc.stroke_width(1)
    gc.stroke('gray50')
    gc.rectangle(40, 50, 250, 180)

    # Draw the circles around the rectangle corners and
    # arc endpoints. All the circles have a 3-pixel radius.
    gc.circle(40,   50,  40+3,  50)
    gc.circle(250, 180, 250+3, 180)
    gc.circle(250, 114, 250+3, 114)
    gc.circle(146,  50, 146+3,  50)

    # Annotate
    gc.stroke('transparent')
    gc.fill("black")
    gc.fill_opacity(1)

    # xMagick recognizes the braces as delimiters.
    gc.gravity(Magick::NorthWestGravity)
    gc.text(43, 45, "{40, 50}")
    gc.text(195, 118, "{0 degrees}")

    gc.gravity(Magick::SouthEastGravity)
    gc.text(300-250, 220-195, "{250, 180}")

    gc.gravity(Magick::NorthGravity)
    gc.text(0, 67, "{270 degrees}")

    # Draw the arc
    gc.fill_opacity(0)
    gc.stroke('red').stroke_width(3)
    gc.arc(40, 50, 250,180, 0, 270)

    # Draw on the canvas
    gc.draw(i)

    i.border!(1,1, "lightcyan2")

    #i.display
    i.write("arc.gif")

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