lua 计算字符串字符个数“中文字算一个字符”

local function GetStringWordNum(str)
    local fontSize = 20
    local lenInByte = #str
    local count = 0
    local i = 1
    while true do
        local curByte = string.byte(str, i)
        if i > lenInByte then
            break
        end
        local byteCount = 1
        if curByte > 0 and curByte < 128 then
            byteCount = 1
        elseif curByte>=128 and curByte<224 then
            byteCount = 2
        elseif curByte>=224 and curByte<240 then
            byteCount = 3
        elseif curByte>=240 and curByte<=247 then
            byteCount = 4
        else
            break
        end
        -- local char = string.sub(str, i, i+byteCount-1)
        i = i + byteCount
        count = count + 1
    end
    return count
end