`window-hscroll' does not report correct value when `text-scale-mode' is on

[路客]

Hi all,

I found `window-hscroll' function does not report a correct value

if `text-scale-mode' is on. A simple test is to enable `ruler-mode'

and edit something like the following "text-ruler":

.........1.........2.........3.........4.........5.........6...
123456789012345678901234567890123456789012345678901234567890...

Now we add a next line with 500 characters and put the cursor at
the end of it; then we use <shift-left_mouse> to decrease the font
size *twice* (with text wrapping disabled and ruler-mode enabled
to observe current `window-hscroll' value). We can now easily see
the `window-hscroll' value is incorrect, by comparing against the

above "text-ruler".

After some experiments I derived the following function that help a
bit but still not a complete answer:

(defun my-hscroll ()
  (round (/ (window-hscroll)
            (or (and (boundp 'text-scale-mode-remapping)
                     (caddr text-scale-mode-remapping))
                1))))

`my-hscroll' function can report a value that is closer to the correct
hscroll value. But the error of `my-hscroll' becomes larger if we again
decrease the font size, or purposely edit a line with 2000 characters.

Is there any way to get the "exact" hscroll value? Say, with pixel-wise

measurement?

Thanks a lot.

--

Best regards,

Luke Lee