util.string.widthindex

local index, remaining, char_width = util.string.widthindex(
    input,
    width,
    ambiguous_as_double = false,
    default_width = 0
)

Type	Name	Description
`string`	input	String to measure
`int`	width	Target display width to find the cutoff for
`bool`	ambiguous_as_double	When true - East Asian "ambiguous width" characters count as double-width instead of single-width
`int`	default_width	Width to use for codepoints with no defined display width

Type	Name	Description
`int`	index	Character index at which the target width is used up
`int`	remaining	Leftover width still available within that character - only returned if the budget ran out mid-string
`int`	char_width	Display width of the character at index - only returned if the budget ran out mid-string

Budget larger than the whole string returns one value

local index = util.string.widthindex("hi", 10)

core.engine.print("info", index) -- 3 (past the end - the whole string fit)

Find a cutoff that lands inside a wide character

local index, remaining, char_width = util.string.widthindex("中文", 1)

core.engine.print("info", index, remaining, char_width) -- 1  1  2

Truncate a string to fit a fixed display width

local text = "hello world"
local index = util.string.widthindex(text, 5)

core.engine.print("info", util.string.sub(text, 1, index)) -- 'hello'