The function generates an output string with triple the length of the input string. The first character of the output string is the input character shifted by 7 positions in the ASCII table, while the second and third characters are fixed as 'g' and 'x', respectively, regardless of the input.

[CODE]: 
```python
def f(x: str) -> str:
    output = ''
    for c in x:
        shifted_char = chr(ord(c) + 7)
        output += shifted_char + 'gx'
    return output
```