This Lua function draws a rounded-corner rectangle when used in the Love game engine. Its parameters are consistent with the love.graphics conventions.

rounded_rectangle.lua

-- This is similar to love.graphics.rectangle, except that the rectangle has
-- rounded corners. r = radius of the corners, n ~ #points used in the polygon.
function rounded_rectangle(mode, x, y, w, h, r, n)
  n = n or 20  -- Number of points in the polygon.
  if n % 4 > 0 then n = n + 4 - (n % 4) end  -- Include multiples of 90 degrees.
  local pts, c, d, i = {}, {x + w / 2, y + h / 2}, {w / 2 - r, r - h / 2}, 0
  while i < n do
    local a = i * 2 * math.pi / n
    local p = {r * math.cos(a), r * math.sin(a)}
    for j = 1, 2 do
      table.insert(pts, c[j] + d[j] + p[j])
      if p[j] * d[j] <= 0 and (p[1] * d[2] < p[2] * d[1]) then
        d[j] = d[j] * -1
        i = i - 1
      end
    end
    i = i + 1
  end
  love.graphics.polygon(mode, pts)
end