-- 传入DrawNode对象，画圆角矩形
function drawNodeRoundRect(drawNode, rect, borderWidth, radius, color, fillColor)
  -- segments表示圆角的精细度，值越大越精细
  local segments    = 100
  local origin      = cc.p(rect.x, rect.y)
  local destination = cc.p(rect.x + rect.width, rect.y - rect.height)
  local points      = {}

  -- 算出1/4圆
  local coef     = math.pi / 2 / segments
  local vertices = {}

  for i=0, segments do
    local rads = (segments - i) * coef
    local x    = radius * math.sin(rads)
    local y    = radius * math.cos(rads)

    table.insert(vertices, cc.p(x, y))
  end

  local tagCenter      = cc.p(0, 0)
  local minX           = math.min(origin.x, destination.x)
  local maxX           = math.max(origin.x, destination.x)
  local minY           = math.min(origin.y, destination.y)
  local maxY           = math.max(origin.y, destination.y)
  local dwPolygonPtMax = (segments + 1) * 4
  local pPolygonPtArr  = {}

  -- 左上角
  tagCenter.x = minX + radius;
  tagCenter.y = maxY - radius;

  for i=0, segments do
    local x = tagCenter.x - vertices[i + 1].x
    local y = tagCenter.y + vertices[i + 1].y

    table.insert(pPolygonPtArr, cc.p(x, y))
  end

  -- 右上角
  tagCenter.x = maxX - radius;
  tagCenter.y = maxY - radius;

  for i=0, segments do
    local x = tagCenter.x + vertices[#vertices - i].x
    local y = tagCenter.y + vertices[#vertices - i].y

    table.insert(pPolygonPtArr, cc.p(x, y))
  end

  -- 右下角
  tagCenter.x = maxX - radius;
  tagCenter.y = minY + radius;

  for i=0, segments do
    local x = tagCenter.x + vertices[i + 1].x
    local y = tagCenter.y - vertices[i + 1].y

    table.insert(pPolygonPtArr, cc.p(x, y))
  end

  -- 左下角
  tagCenter.x = minX + radius;
  tagCenter.y = minY + radius;

  for i=0, segments do
    local x = tagCenter.x - vertices[#vertices - i].x
    local y = tagCenter.y - vertices[#vertices - i].y

    table.insert(pPolygonPtArr, cc.p(x, y))
  end

  if fillColor == nil then
    fillColor = cc.c4f(0, 0, 0, 0)
  end

  drawNode:drawPolygon(pPolygonPtArr, #pPolygonPtArr, fillColor, borderWidth, color)
end

参考：链接描述