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-- Draw a circle
-- @param {image} img
-- @param {integer} x
-- @param {integer} y
-- @param {integer} r
-- @param {integer} lineSize
-- @param {color} drawColor
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on circle (img, x, y, r, lineSize, drawColor)
  props = [:]
  props[#shapeType] = #oval
  props[#lineSize] = lineSize
  props[#color] = drawColor
  img.draw(x-r, y-r, x+r, y+r, props)
end