filterIn

pub fn filterIn(self: *TextEntryWidget, filter_chars: []const u8) void {
    if (filter_chars.len == 0) {
        return;
    }

    var i: usize = 0;
    var j: usize = 0;
    const n = self.len;
    while (i < n) {
        if (std.mem.findScalar(u8, filter_chars, self.text[i]) == null) {
            self.len -= 1;
            var sel = self.textLayout.selection;
            if (sel.start > i) sel.start -= 1;
            if (sel.cursor > i) sel.cursor -= 1;
            if (sel.end > i) sel.end -= 1;
            self.text_changed = true;

            i += 1;
        } else {
            self.text[j] = self.text[i];
            i += 1;
            j += 1;
        }
    }

    if (j < self.text.len)
        self.text[j] = 0;
}