Calculating screen relative X when horizontal scrolling.

[Keith David Bershatsky]

I am having difficulty calculating the screen relative x in the following two 
(2) fact patterns.  How can I calculate the relative x for each fact pattern?


FACT PATTERN # 1:

1.  Current line is horizontally scrolled differently than all other lines in 
the window.

2.  Current line is truncated on the _left_

3.  display-line-numbers is non-nil.

4.  Current line has characters of varying pixel widths.

5.  hscl_temp_p == true


FACT PATTERN # 2:

1.  Current line is horizontally scrolled differently than all other lines in 
the window.

2.  Current line is truncated on the _left_

3.  display-line-numbers is non-nil.

4.  Current line has characters of varying pixel widths.

5.  hscl_perm_p == true


int frame_char_width = FRAME_COLUMN_WIDTH (it->f);

bool auto_hscroll_mode_p = EQ (Fbuffer_local_value (Qauto_hscroll_mode, 
it->w->contents), Qcurrent_line);

it hscl_first_hpos = window_hscroll_limited (it->w, it->f);

/* EXAMPLE:  (scroll-left 5); and, then press the left arrow key one time.*/
bool hscl_temp_p = (!it->w->suspend_auto_hscroll
                    && auto_hscroll_mode_p
                    && it->w->hscroll > 0
                    && it->w->min_hscroll == 0);

/* EXAMPLE:  C-u C-x < and do something that causes the current line to be
             horizontally scrolled differently. */
bool hscl_perm_p = (!it->w->suspend_auto_hscroll
                    && auto_hscroll_mode_p
                    && it->w->hscroll > 0
                    && it->w->min_hscroll > 0
                    && it->w->min_hscroll != it->w->hscroll);

int relative_x;

if (it->current_x > 0
    && hscl_perm_p)
  relative_x = it->current_x - (hscl_first_hpos * frame_char_width);
  else if (it->current_x > 0
           && hscl_temp_p)
    relative_x = it->current_x - (hscl_first_hpos * frame_char_width);