neovim

move.c (83661B)

---

// move.c: Functions for moving the cursor and scrolling text.
//
// There are two ways to move the cursor:
// 1. Move the cursor directly, the text is scrolled to keep the cursor in the
//    window.
// 2. Scroll the text, the cursor is moved into the text visible in the
//    window.
// The 'scrolloff' option makes this a bit complicated.

#include <assert.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

#include "nvim/ascii_defs.h"
#include "nvim/buffer.h"
#include "nvim/buffer_defs.h"
#include "nvim/cursor.h"
#include "nvim/decoration.h"
#include "nvim/diff.h"
#include "nvim/drawscreen.h"
#include "nvim/edit.h"
#include "nvim/errors.h"
#include "nvim/eval/typval.h"
#include "nvim/eval/window.h"
#include "nvim/fold.h"
#include "nvim/getchar.h"
#include "nvim/gettext_defs.h"
#include "nvim/globals.h"
#include "nvim/grid.h"
#include "nvim/grid_defs.h"
#include "nvim/macros_defs.h"
#include "nvim/mark_defs.h"
#include "nvim/mbyte.h"
#include "nvim/memline.h"
#include "nvim/message.h"
#include "nvim/mouse.h"
#include "nvim/move.h"
#include "nvim/normal.h"
#include "nvim/normal_defs.h"
#include "nvim/option.h"
#include "nvim/option_vars.h"
#include "nvim/plines.h"
#include "nvim/popupmenu.h"
#include "nvim/pos_defs.h"
#include "nvim/strings.h"
#include "nvim/types_defs.h"
#include "nvim/vim_defs.h"
#include "nvim/window.h"
#include "nvim/winfloat.h"

typedef struct {
 linenr_T lnum;                // line number
 int fill;                     // filler lines
 int height;                   // height of added line
} lineoff_T;

#include "move.c.generated.h"

/// Get the number of screen lines skipped with "wp->w_skipcol".
static int adjust_plines_for_skipcol(win_T *wp)
{
 if (wp->w_skipcol == 0) {
   return 0;
 }

 int width = wp->w_view_width - win_col_off(wp);
 int w2 = width + win_col_off2(wp);
 if (wp->w_skipcol >= width && w2 > 0) {
   return (wp->w_skipcol - width) / w2 + 1;
 }

 return 0;
}

/// Return how many lines "lnum" will take on the screen, taking into account
/// whether it is the first line, whether w_skipcol is non-zero and limiting to
/// the window height.
int plines_correct_topline(win_T *wp, linenr_T lnum, linenr_T *nextp, bool limit_winheight,
                          bool *foldedp)
{
 int n = plines_win_full(wp, lnum, nextp, foldedp, true, false);
 if (lnum == wp->w_topline) {
   n -= adjust_plines_for_skipcol(wp);
 }
 if (limit_winheight && n > wp->w_view_height) {
   return wp->w_view_height;
 }
 return n;
}

// Compute wp->w_botline for the current wp->w_topline.  Can be called after
// wp->w_topline changed.
static void comp_botline(win_T *wp)
{
 linenr_T lnum;
 int done;

 // If w_cline_row is valid, start there.
 // Otherwise have to start at w_topline.
 check_cursor_moved(wp);
 if (wp->w_valid & VALID_CROW) {
   lnum = wp->w_cursor.lnum;
   done = wp->w_cline_row;
 } else {
   lnum = wp->w_topline;
   done = 0;
 }

 for (; lnum <= wp->w_buffer->b_ml.ml_line_count; lnum++) {
   linenr_T last = lnum;
   bool folded;
   int n = plines_correct_topline(wp, lnum, &last, true, &folded);
   if (lnum <= wp->w_cursor.lnum && last >= wp->w_cursor.lnum) {
     wp->w_cline_row = done;
     wp->w_cline_height = n;
     wp->w_cline_folded = folded;
     redraw_for_cursorline(wp);
     wp->w_valid |= (VALID_CROW|VALID_CHEIGHT);
   }
   if (done + n > wp->w_view_height) {
     break;
   }
   done += n;
   lnum = last;
 }

 // wp->w_botline is the line that is just below the window
 wp->w_botline = lnum;
 wp->w_valid |= VALID_BOTLINE|VALID_BOTLINE_AP;
 wp->w_viewport_invalid = true;

 set_empty_rows(wp, done);

 win_check_anchored_floats(wp);
}

/// Redraw when w_cline_row changes and 'relativenumber' or 'cursorline' is set.
/// Also when concealing is on and 'concealcursor' is not active.
static void redraw_for_cursorline(win_T *wp)
 FUNC_ATTR_NONNULL_ALL
{
 if ((wp->w_valid & VALID_CROW) == 0 && !pum_visible()
     && (wp->w_p_rnu || win_cursorline_standout(wp))) {
   // win_line() will redraw the number column and cursorline only.
   redraw_later(wp, UPD_VALID);
 }
}

/// Redraw when 'concealcursor' is active, or when w_virtcol changes and:
/// - 'cursorcolumn' is set, or
/// - 'cursorlineopt' contains "screenline", or
/// - Visual mode is active.
static void redraw_for_cursorcolumn(win_T *wp)
 FUNC_ATTR_NONNULL_ALL
{
 // If the cursor moves horizontally when 'concealcursor' is active, then the
 // current line needs to be redrawn to calculate the correct cursor position.
 if (wp == curwin && wp->w_p_cole > 0 && conceal_cursor_line(wp)) {
   redrawWinline(wp, wp->w_cursor.lnum);
 }

 if ((wp->w_valid & VALID_VIRTCOL) || pum_visible()) {
   return;
 }

 if (wp->w_p_cuc) {
   // When 'cursorcolumn' is set need to redraw with UPD_SOME_VALID.
   redraw_later(wp, UPD_SOME_VALID);
 } else if (wp->w_p_cul && (wp->w_p_culopt_flags & kOptCuloptFlagScreenline)) {
   // When 'cursorlineopt' contains "screenline" need to redraw with UPD_VALID.
   redraw_later(wp, UPD_VALID);
 }

 // When current buffer's cursor moves in Visual mode, redraw it with UPD_INVERTED.
 if (VIsual_active && wp->w_buffer == curbuf) {
   redraw_buf_later(curbuf, UPD_INVERTED);
 }
}

/// Set wp->w_virtcol to a value ("vcol") that is already valid.
/// Handles redrawing if wp->w_virtcol was previously invalid.
void set_valid_virtcol(win_T *wp, colnr_T vcol)
{
 wp->w_virtcol = vcol;
 redraw_for_cursorcolumn(wp);
 wp->w_valid |= VALID_VIRTCOL;
}

/// Calculates how much the 'listchars' "precedes" or 'smoothscroll' "<<<"
/// marker overlaps with buffer text for window "wp".
/// Parameter "extra2" should be the padding on the 2nd line, not the first
/// line. When "extra2" is -1 calculate the padding.
/// Returns the number of columns of overlap with buffer text, excluding the
/// extra padding on the ledge.
int sms_marker_overlap(win_T *wp, int extra2)
{
 if (extra2 == -1) {
   extra2 = win_col_off(wp) - win_col_off2(wp);
 }
 // There is no marker overlap when in showbreak mode, thus no need to
 // account for it.  See wlv_put_linebuf().
 if (*get_showbreak_value(wp) != NUL) {
   return 0;
 }

 // Overlap when 'list' and 'listchars' "precedes" are set is 1.
 if (wp->w_p_list && wp->w_p_lcs_chars.prec) {
   return 1;
 }

 return extra2 > 3 ? 0 : 3 - extra2;
}

/// Calculates the skipcol offset for window "wp" given how many
/// physical lines we want to scroll down.
static int skipcol_from_plines(win_T *wp, int plines_off)
{
 int width1 = wp->w_view_width - win_col_off(wp);

 int skipcol = 0;
 if (plines_off > 0) {
   skipcol += width1;
 }
 if (plines_off > 1) {
   skipcol += (width1 + win_col_off2(wp)) * (plines_off - 1);
 }
 return skipcol;
}

/// Set wp->w_skipcol to zero and redraw later if needed.
static void reset_skipcol(win_T *wp)
{
 if (wp->w_skipcol == 0) {
   return;
 }

 wp->w_skipcol = 0;

 // Should use the least expensive way that displays all that changed.
 // UPD_NOT_VALID is too expensive, UPD_REDRAW_TOP does not redraw
 // enough when the top line gets another screen line.
 redraw_later(wp, UPD_SOME_VALID);
}

// Update wp->w_topline to move the cursor onto the screen.
void update_topline(win_T *wp)
{
 bool check_botline = false;
 OptInt *so_ptr = wp->w_p_so >= 0 ? &wp->w_p_so : &p_so;
 OptInt save_so = *so_ptr;

 // Cursor is updated instead when this is true for 'splitkeep'.
 if (skip_update_topline) {
   return;
 }

 // If there is no valid screen and when the window height is zero just use
 // the cursor line.
 if (!default_grid.chars || wp->w_view_height == 0) {
   check_cursor_lnum(wp);
   wp->w_topline = wp->w_cursor.lnum;
   wp->w_botline = wp->w_topline;
   wp->w_viewport_invalid = true;
   wp->w_scbind_pos = 1;
   return;
 }

 check_cursor_moved(wp);
 if (wp->w_valid & VALID_TOPLINE) {
   return;
 }

 // When dragging with the mouse, don't scroll that quickly
 if (mouse_dragging > 0) {
   *so_ptr = mouse_dragging - 1;
 }

 linenr_T old_topline = wp->w_topline;
 int old_topfill = wp->w_topfill;

 // If the buffer is empty, always set topline to 1.
 if (buf_is_empty(wp->w_buffer)) {  // special case - file is empty
   if (wp->w_topline != 1) {
     redraw_later(wp, UPD_NOT_VALID);
   }
   wp->w_topline = 1;
   wp->w_botline = 2;
   wp->w_skipcol = 0;
   wp->w_valid |= VALID_BOTLINE|VALID_BOTLINE_AP;
   wp->w_viewport_invalid = true;
   wp->w_scbind_pos = 1;
 } else {
   bool check_topline = false;
   // If the cursor is above or near the top of the window, scroll the window
   // to show the line the cursor is in, with 'scrolloff' context.
   if (wp->w_topline > 1 || wp->w_skipcol > 0) {
     // If the cursor is above topline, scrolling is always needed.
     // If the cursor is far below topline and there is no folding,
     // scrolling down is never needed.
     if (wp->w_cursor.lnum < wp->w_topline) {
       check_topline = true;
     } else if (check_top_offset(wp)) {
       check_topline = true;
     } else if (wp->w_skipcol > 0 && wp->w_cursor.lnum == wp->w_topline) {
       colnr_T vcol;

       // Check that the cursor position is visible.  Add columns for
       // the marker displayed in the top-left if needed.
       getvvcol(wp, &wp->w_cursor, &vcol, NULL, NULL);
       int overlap = sms_marker_overlap(wp, -1);
       if (wp->w_skipcol + overlap > vcol) {
         check_topline = true;
       }
     }
   }
   // Check if there are more filler lines than allowed.
   if (!check_topline && wp->w_topfill > win_get_fill(wp, wp->w_topline)) {
     check_topline = true;
   }

   if (check_topline) {
     int halfheight = wp->w_view_height / 2 - 1;
     if (halfheight < 2) {
       halfheight = 2;
     }
     int64_t n;
     if (win_lines_concealed(wp)) {
       // Count the number of logical lines between the cursor and
       // topline + p_so (approximation of how much will be
       // scrolled).
       n = 0;
       for (linenr_T lnum = wp->w_cursor.lnum; lnum < wp->w_topline + *so_ptr; lnum++) {
         // stop at end of file or when we know we are far off
         assert(wp->w_buffer != 0);
         if (lnum >= wp->w_buffer->b_ml.ml_line_count
             || (n += !decor_conceal_line(wp, lnum, false)) >= halfheight) {
           break;
         }
         hasFolding(wp, lnum, NULL, &lnum);
       }
     } else {
       n = wp->w_topline + *so_ptr - wp->w_cursor.lnum;
     }

     // If we weren't very close to begin with, we scroll to put the
     // cursor in the middle of the window.  Otherwise put the cursor
     // near the top of the window.
     if (n >= halfheight) {
       scroll_cursor_halfway(wp, false, false);
     } else {
       scroll_cursor_top(wp, scrolljump_value(wp), false);
       check_botline = true;
     }
   } else {
     // Make sure topline is the first line of a fold.
     hasFolding(wp, wp->w_topline, &wp->w_topline, NULL);
     check_botline = true;
   }
 }

 // If the cursor is below the bottom of the window, scroll the window
 // to put the cursor on the window.
 // When w_botline is invalid, recompute it first, to avoid a redraw later.
 // If w_botline was approximated, we might need a redraw later in a few
 // cases, but we don't want to spend (a lot of) time recomputing w_botline
 // for every small change.
 if (check_botline) {
   if (!(wp->w_valid & VALID_BOTLINE_AP)) {
     validate_botline_win(wp);
   }

   assert(wp->w_buffer != 0);
   if (wp->w_botline <= wp->w_buffer->b_ml.ml_line_count) {
     if (wp->w_cursor.lnum < wp->w_botline) {
       if ((wp->w_cursor.lnum >= wp->w_botline - *so_ptr || win_lines_concealed(wp))) {
         lineoff_T loff;

         // Cursor is (a few lines) above botline, check if there are
         // 'scrolloff' window lines below the cursor.  If not, need to
         // scroll.
         int n = wp->w_empty_rows;
         loff.lnum = wp->w_cursor.lnum;
         // In a fold go to its last line.
         hasFolding(wp, loff.lnum, NULL, &loff.lnum);
         loff.fill = 0;
         n += wp->w_filler_rows;
         loff.height = 0;
         while (loff.lnum < wp->w_botline
                && (loff.lnum + 1 < wp->w_botline || loff.fill == 0)) {
           n += loff.height;
           if (n >= *so_ptr) {
             break;
           }
           botline_forw(wp, &loff);
         }
         if (n >= *so_ptr) {
           // sufficient context, no need to scroll
           check_botline = false;
         }
       } else {
         // sufficient context, no need to scroll
         check_botline = false;
       }
     }
     if (check_botline) {
       int n = 0;
       if (win_lines_concealed(wp)) {
         // Count the number of logical lines between the cursor and
         // botline - p_so (approximation of how much will be
         // scrolled).
         for (linenr_T lnum = wp->w_cursor.lnum; lnum >= wp->w_botline - *so_ptr; lnum--) {
           // stop at end of file or when we know we are far off
           if (lnum <= 0
               || (n += !decor_conceal_line(wp, lnum - 1, false)) > wp->w_view_height + 1) {
             break;
           }
           hasFolding(wp, lnum, &lnum, NULL);
         }
       } else {
         n = wp->w_cursor.lnum - wp->w_botline + 1 + (int)(*so_ptr);
       }
       if (n <= wp->w_view_height + 1) {
         scroll_cursor_bot(wp, scrolljump_value(wp), false);
       } else {
         scroll_cursor_halfway(wp, false, false);
       }
     }
   }
 }
 wp->w_valid |= VALID_TOPLINE;
 wp->w_viewport_invalid = true;
 win_check_anchored_floats(wp);

 // Need to redraw when topline changed.
 if (wp->w_topline != old_topline
     || wp->w_topfill != old_topfill) {
   dollar_vcol = -1;
   redraw_later(wp, UPD_VALID);

   // When 'smoothscroll' is not set, should reset w_skipcol.
   if (!wp->w_p_sms) {
     reset_skipcol(wp);
   } else if (wp->w_skipcol != 0) {
     redraw_later(wp, UPD_SOME_VALID);
   }

   // May need to set w_skipcol when cursor in w_topline.
   if (wp->w_cursor.lnum == wp->w_topline) {
     validate_cursor(wp);
   }
 }

 *so_ptr = save_so;
}

/// Return the scrolljump value to use for the window "wp".
/// When 'scrolljump' is positive use it as-is.
/// When 'scrolljump' is negative use it as a percentage of the window height.
static int scrolljump_value(win_T *wp)
{
 int result = p_sj >= 0 ? (int)p_sj : (wp->w_view_height * (int)(-p_sj)) / 100;
 return result;
}

/// Return true when there are not 'scrolloff' lines above the cursor for window "wp".
static bool check_top_offset(win_T *wp)
{
 int so = get_scrolloff_value(wp);
 if (wp->w_cursor.lnum < wp->w_topline + so || win_lines_concealed(wp)) {
   lineoff_T loff;
   loff.lnum = wp->w_cursor.lnum;
   loff.fill = 0;
   int n = wp->w_topfill;  // always have this context
   // Count the visible screen lines above the cursor line.
   while (n < so) {
     topline_back(wp, &loff);
     // Stop when included a line above the window.
     if (loff.lnum < wp->w_topline
         || (loff.lnum == wp->w_topline && loff.fill > 0)) {
       break;
     }
     n += loff.height;
   }
   if (n < so) {
     return true;
   }
 }
 return false;
}

/// Update w_curswant.
void update_curswant_force(void)
{
 validate_virtcol(curwin);
 curwin->w_curswant = curwin->w_virtcol;
 curwin->w_set_curswant = false;
}

/// Update w_curswant if w_set_curswant is set.
void update_curswant(void)
{
 if (curwin->w_set_curswant) {
   update_curswant_force();
 }
}

// Check if the cursor has moved.  Set the w_valid flag accordingly.
void check_cursor_moved(win_T *wp)
{
 if (wp->w_cursor.lnum != wp->w_valid_cursor.lnum) {
   wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL
                    |VALID_CHEIGHT|VALID_CROW|VALID_TOPLINE);

   // Concealed line visibility toggled.
   if (wp == curwin && wp->w_valid_cursor.lnum > 0 && wp->w_p_cole >= 2
       && !conceal_cursor_line(wp)
       && (decor_conceal_line(wp, wp->w_cursor.lnum - 1, true)
           || decor_conceal_line(wp, wp->w_valid_cursor.lnum - 1, true))) {
     changed_window_setting(wp);
   }
   wp->w_valid_cursor = wp->w_cursor;
   wp->w_valid_leftcol = wp->w_leftcol;
   wp->w_valid_skipcol = wp->w_skipcol;
   wp->w_viewport_invalid = true;
 } else if (wp->w_skipcol != wp->w_valid_skipcol) {
   wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL
                    |VALID_CHEIGHT|VALID_CROW
                    |VALID_BOTLINE|VALID_BOTLINE_AP);
   wp->w_valid_cursor = wp->w_cursor;
   wp->w_valid_leftcol = wp->w_leftcol;
   wp->w_valid_skipcol = wp->w_skipcol;
 } else if (wp->w_cursor.col != wp->w_valid_cursor.col
            || wp->w_leftcol != wp->w_valid_leftcol
            || wp->w_cursor.coladd !=
            wp->w_valid_cursor.coladd) {
   wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL);
   wp->w_valid_cursor.col = wp->w_cursor.col;
   wp->w_valid_leftcol = wp->w_leftcol;
   wp->w_valid_cursor.coladd = wp->w_cursor.coladd;
   wp->w_viewport_invalid = true;
 }
}

// Call this function when some window settings have changed, which require
// the cursor position, botline and topline to be recomputed and the window to
// be redrawn.  E.g, when changing the 'wrap' option or folding.
void changed_window_setting(win_T *wp)
{
 wp->w_lines_valid = 0;
 changed_line_abv_curs_win(wp);
 wp->w_valid &= ~(VALID_BOTLINE|VALID_BOTLINE_AP|VALID_TOPLINE);
 redraw_later(wp, UPD_NOT_VALID);
}

/// Call changed_window_setting() for every window.
void changed_window_setting_all(void)
{
 FOR_ALL_TAB_WINDOWS(tp, wp) {
   changed_window_setting(wp);
 }
}

// Set wp->w_topline to a certain number.
void set_topline(win_T *wp, linenr_T lnum)
{
 linenr_T prev_topline = wp->w_topline;

 // go to first of folded lines
 hasFolding(wp, lnum, &lnum, NULL);
 // Approximate the value of w_botline
 wp->w_botline += lnum - wp->w_topline;
 if (wp->w_botline > wp->w_buffer->b_ml.ml_line_count + 1) {
   wp->w_botline = wp->w_buffer->b_ml.ml_line_count + 1;
 }
 wp->w_topline = lnum;
 wp->w_topline_was_set = true;
 if (lnum != prev_topline) {
   // Keep the filler lines when the topline didn't change.
   wp->w_topfill = 0;
 }
 wp->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE|VALID_TOPLINE);
 // Don't set VALID_TOPLINE here, 'scrolloff' needs to be checked.
 redraw_later(wp, UPD_VALID);
}

/// Call this function when the length of the cursor line (in screen
/// characters) has changed, and the change is before the cursor.
/// If the line length changed the number of screen lines might change,
/// requiring updating w_topline.  That may also invalidate w_crow.
/// Need to take care of w_botline separately!
void changed_cline_bef_curs(win_T *wp)
{
 wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL|VALID_CROW
                  |VALID_CHEIGHT|VALID_TOPLINE);
}

// Call this function when the length of a line (in screen characters) above
// the cursor have changed.
// Need to take care of w_botline separately!
void changed_line_abv_curs(void)
{
 curwin->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL|VALID_CROW
                      |VALID_CHEIGHT|VALID_TOPLINE);
}

void changed_line_abv_curs_win(win_T *wp)
{
 wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL|VALID_CROW
                  |VALID_CHEIGHT|VALID_TOPLINE);
}

/// Make sure the value of wp->w_botline is valid.
void validate_botline_win(win_T *wp)
 FUNC_ATTR_NONNULL_ALL
{
 if (!(wp->w_valid & VALID_BOTLINE)) {
   comp_botline(wp);
 }
}

/// Mark wp->w_botline as invalid (because of some change in the buffer).
void invalidate_botline_win(win_T *wp)
 FUNC_ATTR_NONNULL_ALL
{
 wp->w_valid &= ~(VALID_BOTLINE|VALID_BOTLINE_AP);
}

void approximate_botline_win(win_T *wp)
{
 wp->w_valid &= ~VALID_BOTLINE;
}

// Return true if wp->w_wrow and wp->w_wcol are valid.
int cursor_valid(win_T *wp)
{
 check_cursor_moved(wp);
 return (wp->w_valid & (VALID_WROW|VALID_WCOL)) == (VALID_WROW|VALID_WCOL);
}

// Validate cursor position.  Makes sure w_wrow and w_wcol are valid.
// w_topline must be valid, you may need to call update_topline() first!
void validate_cursor(win_T *wp)
{
 check_cursor_lnum(wp);
 check_cursor_moved(wp);
 if ((wp->w_valid & (VALID_WCOL|VALID_WROW)) != (VALID_WCOL|VALID_WROW)) {
   curs_columns(wp, true);
 }
}

// Compute wp->w_cline_row and wp->w_cline_height, based on the current value
// of wp->w_topline.
static void curs_rows(win_T *wp)
{
 // Check if wp->w_lines[].wl_size is invalid
 bool all_invalid = (!redrawing()
                     || wp->w_lines_valid == 0
                     || wp->w_lines[0].wl_lnum > wp->w_topline);
 int i = 0;
 wp->w_cline_row = 0;
 for (linenr_T lnum = wp->w_topline; lnum < wp->w_cursor.lnum; i++) {
   bool valid = false;
   if (!all_invalid && i < wp->w_lines_valid) {
     if (wp->w_lines[i].wl_lnum < lnum || !wp->w_lines[i].wl_valid) {
       continue;                       // skip changed or deleted lines
     }
     if (wp->w_lines[i].wl_lnum == lnum) {
       // Check for newly inserted lines below this row, in which
       // case we need to check for folded lines.
       if (!wp->w_buffer->b_mod_set
           || wp->w_lines[i].wl_lastlnum < wp->w_cursor.lnum
           || wp->w_buffer->b_mod_top
           > wp->w_lines[i].wl_lastlnum + 1) {
         valid = true;
       }
     } else if (wp->w_lines[i].wl_lnum > lnum) {
       i--;                            // hold at inserted lines
     }
   }
   if (valid && (lnum != wp->w_topline || (wp->w_skipcol == 0 && !win_may_fill(wp)))) {
     lnum = wp->w_lines[i].wl_lastlnum + 1;
     // Cursor inside folded or concealed lines, don't count this row
     if (lnum > wp->w_cursor.lnum) {
       break;
     }
     wp->w_cline_row += wp->w_lines[i].wl_size;
   } else {
     linenr_T last = lnum;
     bool folded;
     int n = plines_correct_topline(wp, lnum, &last, true, &folded);
     lnum = last + 1;
     if (lnum + decor_conceal_line(wp, lnum - 1, false) > wp->w_cursor.lnum) {
       break;
     }
     wp->w_cline_row += n;
   }
 }

 check_cursor_moved(wp);
 if (!(wp->w_valid & VALID_CHEIGHT)) {
   if (all_invalid
       || i == wp->w_lines_valid
       || (i < wp->w_lines_valid
           && (!wp->w_lines[i].wl_valid
               || wp->w_lines[i].wl_lnum != wp->w_cursor.lnum))) {
     wp->w_cline_height = plines_win_full(wp, wp->w_cursor.lnum, NULL,
                                          &wp->w_cline_folded, true, true);
   } else if (i > wp->w_lines_valid) {
     // a line that is too long to fit on the last screen line
     wp->w_cline_height = 0;
     wp->w_cline_folded = hasFolding(wp, wp->w_cursor.lnum, NULL, NULL);
   } else {
     wp->w_cline_height = wp->w_lines[i].wl_size;
     wp->w_cline_folded = wp->w_lines[i].wl_folded;
   }
 }

 redraw_for_cursorline(wp);
 wp->w_valid |= VALID_CROW|VALID_CHEIGHT;
}

// Validate wp->w_virtcol only.
void validate_virtcol(win_T *wp)
{
 check_cursor_moved(wp);

 if (wp->w_valid & VALID_VIRTCOL) {
   return;
 }

 getvvcol(wp, &wp->w_cursor, NULL, &(wp->w_virtcol), NULL);
 redraw_for_cursorcolumn(wp);
 wp->w_valid |= VALID_VIRTCOL;
}

// Validate wp->w_cline_height only.
void validate_cheight(win_T *wp)
{
 check_cursor_moved(wp);

 if (wp->w_valid & VALID_CHEIGHT) {
   return;
 }

 wp->w_cline_height = plines_win_full(wp, wp->w_cursor.lnum,
                                      NULL, &wp->w_cline_folded,
                                      true, true);
 wp->w_valid |= VALID_CHEIGHT;
}

// Validate w_wcol and w_virtcol only.
void validate_cursor_col(win_T *wp)
{
 validate_virtcol(wp);

 if (wp->w_valid & VALID_WCOL) {
   return;
 }

 colnr_T col = wp->w_virtcol;
 colnr_T off = win_col_off(wp);
 col += off;
 int width = wp->w_view_width - off + win_col_off2(wp);

 // long line wrapping, adjust wp->w_wrow
 if (wp->w_p_wrap && col >= (colnr_T)wp->w_view_width && width > 0) {
   // use same formula as what is used in curs_columns()
   col -= ((col - wp->w_view_width) / width + 1) * width;
 }
 if (col > (int)wp->w_leftcol) {
   col -= wp->w_leftcol;
 } else {
   col = 0;
 }
 wp->w_wcol = col;

 wp->w_valid |= VALID_WCOL;
}

// Compute offset of a window, occupied by absolute or relative line number,
// fold column and sign column (these don't move when scrolling horizontally).
int win_col_off(win_T *wp)
{
 return ((wp->w_p_nu || wp->w_p_rnu || *wp->w_p_stc != NUL)
         ? (number_width(wp) + (*wp->w_p_stc == NUL)) : 0)
        + ((wp != cmdwin_win) ? 0 : 1)
        + win_fdccol_count(wp) + (wp->w_scwidth * SIGN_WIDTH);
}

// Return the difference in column offset for the second screen line of a
// wrapped line.  It's positive if 'number' or 'relativenumber' is on and 'n'
// is in 'cpoptions'.
int win_col_off2(win_T *wp)
{
 if ((wp->w_p_nu || wp->w_p_rnu || *wp->w_p_stc != NUL)
     && vim_strchr(p_cpo, CPO_NUMCOL) != NULL) {
   return number_width(wp) + (*wp->w_p_stc == NUL);
 }
 return 0;
}

// Compute wp->w_wcol and wp->w_virtcol.
// Also updates wp->w_wrow and wp->w_cline_row.
// Also updates wp->w_leftcol.
// @param may_scroll when true, may scroll horizontally
void curs_columns(win_T *wp, int may_scroll)
{
 colnr_T startcol;
 colnr_T endcol;

 // First make sure that w_topline is valid (after moving the cursor).
 update_topline(wp);

 // Next make sure that w_cline_row is valid.
 if (!(wp->w_valid & VALID_CROW)) {
   curs_rows(wp);
 }

 // Compute the number of virtual columns.
 if (wp->w_cline_folded) {
   // In a folded line the cursor is always in the first column
   startcol = wp->w_virtcol = endcol = wp->w_leftcol;
 } else {
   getvvcol(wp, &wp->w_cursor, &startcol, &(wp->w_virtcol), &endcol);
 }

 // remove '$' from change command when cursor moves onto it
 if (startcol > dollar_vcol) {
   dollar_vcol = -1;
 }

 int extra = win_col_off(wp);
 wp->w_wcol = wp->w_virtcol + extra;
 endcol += extra;

 // Now compute w_wrow, counting screen lines from w_cline_row.
 wp->w_wrow = wp->w_cline_row;

 int n;
 int width1 = wp->w_view_width - extra;  // text width for first screen line
 int width2 = 0;                          // text width for second and later screen line
 bool did_sub_skipcol = false;
 if (width1 <= 0) {
   // No room for text, put cursor in last char of window.
   // If not wrapping, the last non-empty line.
   wp->w_wcol = wp->w_view_width - 1;
   if (wp->w_p_wrap) {
     wp->w_wrow = wp->w_view_height - 1;
   } else {
     wp->w_wrow = wp->w_view_height - 1 - wp->w_empty_rows;
   }
 } else if (wp->w_p_wrap && wp->w_view_width != 0) {
   width2 = width1 + win_col_off2(wp);

   // skip columns that are not visible
   if (wp->w_cursor.lnum == wp->w_topline
       && wp->w_skipcol > 0
       && wp->w_wcol >= wp->w_skipcol) {
     // Deduct by multiples of width2.  This allows the long line wrapping
     // formula below to correctly calculate the w_wcol value when wrapping.
     if (wp->w_skipcol <= width1) {
       wp->w_wcol -= width2;
     } else {
       wp->w_wcol -= width2 * (((wp->w_skipcol - width1) / width2) + 1);
     }

     did_sub_skipcol = true;
   }

   // long line wrapping, adjust wp->w_wrow
   if (wp->w_wcol >= wp->w_view_width) {
     // this same formula is used in validate_cursor_col()
     n = (wp->w_wcol - wp->w_view_width) / width2 + 1;
     wp->w_wcol -= n * width2;
     wp->w_wrow += n;
   }
 } else if (may_scroll
            && !wp->w_cline_folded) {
   // No line wrapping: compute wp->w_leftcol if scrolling is on and line
   // is not folded.
   // If scrolling is off, wp->w_leftcol is assumed to be 0

   // If Cursor is left of the screen, scroll rightwards.
   // If Cursor is right of the screen, scroll leftwards
   // If we get closer to the edge than 'sidescrolloff', scroll a little
   // extra
   int siso = get_sidescrolloff_value(wp);
   int off_left = startcol - wp->w_leftcol - siso;
   int off_right = endcol - wp->w_leftcol - wp->w_view_width + siso + 1;
   if (off_left < 0 || off_right > 0) {
     int diff = (off_left < 0) ? -off_left : off_right;

     // When far off or not enough room on either side, put cursor in
     // middle of window.
     int new_leftcol;
     if (p_ss == 0 || diff >= width1 / 2 || off_right >= off_left) {
       new_leftcol = wp->w_wcol - extra - width1 / 2;
     } else {
       if (diff < p_ss) {
         assert(p_ss <= INT_MAX);
         diff = (int)p_ss;
       }
       if (off_left < 0) {
         new_leftcol = wp->w_leftcol - diff;
       } else {
         new_leftcol = wp->w_leftcol + diff;
       }
     }
     new_leftcol = MAX(new_leftcol, 0);
     if (new_leftcol != (int)wp->w_leftcol) {
       wp->w_leftcol = new_leftcol;
       win_check_anchored_floats(wp);
       // screen has to be redrawn with new wp->w_leftcol
       redraw_later(wp, UPD_NOT_VALID);
     }
   }
   wp->w_wcol -= wp->w_leftcol;
 } else if (wp->w_wcol > (int)wp->w_leftcol) {
   wp->w_wcol -= wp->w_leftcol;
 } else {
   wp->w_wcol = 0;
 }

 // Skip over filler lines.  At the top use w_topfill, there
 // may be some filler lines above the window.
 if (wp->w_cursor.lnum == wp->w_topline) {
   wp->w_wrow += wp->w_topfill;
 } else {
   wp->w_wrow += win_get_fill(wp, wp->w_cursor.lnum);
 }

 int plines = 0;
 int so = get_scrolloff_value(wp);
 colnr_T prev_skipcol = wp->w_skipcol;
 if ((wp->w_wrow >= wp->w_view_height
      || ((prev_skipcol > 0
           || wp->w_wrow + so >= wp->w_view_height)
          && (plines = plines_win_nofill(wp, wp->w_cursor.lnum, false)) - 1
          >= wp->w_view_height))
     && wp->w_view_height != 0
     && wp->w_cursor.lnum == wp->w_topline
     && width2 > 0
     && wp->w_view_width != 0) {
   // Cursor past end of screen.  Happens with a single line that does
   // not fit on screen.  Find a skipcol to show the text around the
   // cursor.  Avoid scrolling all the time. compute value of "extra":
   // 1: Less than "p_so" lines above
   // 2: Less than "p_so" lines below
   // 3: both of them
   extra = 0;
   if (wp->w_skipcol + so * width2 > wp->w_virtcol) {
     extra = 1;
   }
   // Compute last display line of the buffer line that we want at the
   // bottom of the window.
   if (plines == 0) {
     plines = plines_win(wp, wp->w_cursor.lnum, false);
   }
   plines--;
   if (plines > wp->w_wrow + so) {
     assert(so <= INT_MAX);
     n = wp->w_wrow + so;
   } else {
     n = plines;
   }
   if ((colnr_T)n >= wp->w_view_height + wp->w_skipcol / width2 - so) {
     extra += 2;
   }

   if (extra == 3 || wp->w_view_height <= so * 2) {
     // not enough room for 'scrolloff', put cursor in the middle
     n = wp->w_virtcol / width2;
     if (n > wp->w_view_height / 2) {
       n -= wp->w_view_height / 2;
     } else {
       n = 0;
     }
     // don't skip more than necessary
     if (n > plines - wp->w_view_height + 1) {
       n = plines - wp->w_view_height + 1;
     }
     wp->w_skipcol = n > 0 ? width1 + (n - 1) * width2
                           : 0;
   } else if (extra == 1) {
     // less than 'scrolloff' lines above, decrease skipcol
     assert(so <= INT_MAX);
     extra = (wp->w_skipcol + so * width2 - wp->w_virtcol + width2 - 1) / width2;
     if (extra > 0) {
       if ((colnr_T)(extra * width2) > wp->w_skipcol) {
         extra = wp->w_skipcol / width2;
       }
       wp->w_skipcol -= extra * width2;
     }
   } else if (extra == 2) {
     // less than 'scrolloff' lines below, increase skipcol
     endcol = (n - wp->w_view_height + 1) * width2;
     while (endcol > wp->w_virtcol) {
       endcol -= width2;
     }
     wp->w_skipcol = MAX(wp->w_skipcol, endcol);
   }

   // adjust w_wrow for the changed w_skipcol
   if (did_sub_skipcol) {
     wp->w_wrow -= (wp->w_skipcol - prev_skipcol) / width2;
   } else {
     wp->w_wrow -= wp->w_skipcol / width2;
   }

   if (wp->w_wrow >= wp->w_view_height) {
     // small window, make sure cursor is in it
     extra = wp->w_wrow - wp->w_view_height + 1;
     wp->w_skipcol += extra * width2;
     wp->w_wrow -= extra;
   }

   // extra could be either positive or negative
   extra = (prev_skipcol - wp->w_skipcol) / width2;
   // TODO(bfredl): this is very suspicious when not called by win_update()
   // We should not randomly alter screen state outside of update_screen() :(
   if (wp->w_grid.target) {
     win_scroll_lines(wp, 0, extra);
   }
 } else if (!wp->w_p_sms) {
   wp->w_skipcol = 0;
 }
 if (prev_skipcol != wp->w_skipcol) {
   redraw_later(wp, UPD_SOME_VALID);
 }

 redraw_for_cursorcolumn(wp);

 // now w_leftcol and w_skipcol are valid, avoid check_cursor_moved()
 // thinking otherwise
 wp->w_valid_leftcol = wp->w_leftcol;
 wp->w_valid_skipcol = wp->w_skipcol;

 wp->w_valid |= VALID_WCOL|VALID_WROW|VALID_VIRTCOL;
}

/// Compute the screen position of text character at "pos" in window "wp"
/// The resulting values are one-based, zero when character is not visible.
///
/// @param[out] rowp screen row
/// @param[out] scolp start screen column
/// @param[out] ccolp cursor screen column
/// @param[out] ecolp end screen column
void textpos2screenpos(win_T *wp, pos_T *pos, int *rowp, int *scolp, int *ccolp, int *ecolp,
                      bool local)
{
 colnr_T scol = 0;
 colnr_T ccol = 0;
 colnr_T ecol = 0;
 int row = 0;
 colnr_T coloff = 0;
 bool visible_row = false;
 bool is_folded = false;

 linenr_T lnum = pos->lnum;
 if (lnum >= wp->w_topline && lnum <= wp->w_botline) {
   is_folded = hasFolding(wp, lnum, &lnum, NULL);
   row = plines_m_win(wp, wp->w_topline, lnum - 1, INT_MAX);
   // "row" should be the screen line where line "lnum" begins, which can
   // be negative if "lnum" is "w_topline" and "w_skipcol" is non-zero.
   row -= adjust_plines_for_skipcol(wp);
   // Add filler lines above this buffer line.
   row += lnum == wp->w_topline ? wp->w_topfill : win_get_fill(wp, lnum);
   visible_row = true;
 } else if (!local || lnum < wp->w_topline) {
   row = 0;
 } else {
   row = wp->w_view_height - 1;
 }

 bool existing_row = (lnum > 0 && lnum <= wp->w_buffer->b_ml.ml_line_count);

 if ((local || visible_row) && existing_row) {
   const colnr_T off = win_col_off(wp);
   if (is_folded) {
     row += (local ? 0 : wp->w_winrow + wp->w_winrow_off) + 1;
     coloff = (local ? 0 : wp->w_wincol + wp->w_wincol_off) + 1 + off;
   } else {
     assert(lnum == pos->lnum);
     getvcol(wp, pos, &scol, &ccol, &ecol);

     // similar to what is done in validate_cursor_col()
     colnr_T col = scol;
     col += off;
     int width = wp->w_view_width - off + win_col_off2(wp);

     // long line wrapping, adjust row
     if (wp->w_p_wrap && col >= (colnr_T)wp->w_view_width && width > 0) {
       // use same formula as what is used in curs_columns()
       int rowoff = visible_row ? ((col - wp->w_view_width) / width + 1) : 0;
       col -= rowoff * width;
       row += rowoff;
     }

     col -= wp->w_leftcol;

     if (col >= 0 && col < wp->w_view_width && row >= 0 && row < wp->w_view_height) {
       coloff = col - scol + (local ? 0 : wp->w_wincol + wp->w_wincol_off) + 1;
       row += (local ? 0 : wp->w_winrow + wp->w_winrow_off) + 1;
     } else {
       // character is left, right or below of the window
       scol = ccol = ecol = 0;
       if (local) {
         coloff = col < 0 ? -1 : wp->w_view_width + 1;
       } else {
         row = 0;
       }
     }
   }
 }
 *rowp = row;
 *scolp = scol + coloff;
 *ccolp = ccol + coloff;
 *ecolp = ecol + coloff;
}

/// "screenpos({winid}, {lnum}, {col})" function
void f_screenpos(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
{
 tv_dict_alloc_ret(rettv);
 dict_T *dict = rettv->vval.v_dict;

 win_T *wp = find_win_by_nr_or_id(&argvars[0]);
 if (wp == NULL) {
   return;
 }

 pos_T pos = {
   .lnum = (linenr_T)tv_get_number(&argvars[1]),
   .col = (colnr_T)tv_get_number(&argvars[2]) - 1,
   .coladd = 0
 };
 if (pos.lnum > wp->w_buffer->b_ml.ml_line_count) {
   semsg(_(e_invalid_line_number_nr), pos.lnum);
   return;
 }
 pos.col = MAX(pos.col, 0);
 int row = 0;
 int scol = 0;
 int ccol = 0;
 int ecol = 0;
 textpos2screenpos(wp, &pos, &row, &scol, &ccol, &ecol, false);

 tv_dict_add_nr(dict, S_LEN("row"), row);
 tv_dict_add_nr(dict, S_LEN("col"), scol);
 tv_dict_add_nr(dict, S_LEN("curscol"), ccol);
 tv_dict_add_nr(dict, S_LEN("endcol"), ecol);
}

/// Convert a virtual (screen) column to a character column.  The first column
/// is one.  For a multibyte character, the column number of the first byte is
/// returned.
static int virtcol2col(win_T *wp, linenr_T lnum, int vcol)
{
 int offset = vcol2col(wp, lnum, vcol - 1, NULL);
 char *line = ml_get_buf(wp->w_buffer, lnum);
 char *p = line + offset;

 if (*p == NUL) {
   if (p == line) {  // empty line
     return 0;
   }
   // Move to the first byte of the last char.
   MB_PTR_BACK(line, p);
 }
 return (int)(p - line + 1);
}

/// "virtcol2col({winid}, {lnum}, {col})" function
void f_virtcol2col(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
{
 rettv->vval.v_number = -1;

 if (tv_check_for_number_arg(argvars, 0) == FAIL
     || tv_check_for_number_arg(argvars, 1) == FAIL
     || tv_check_for_number_arg(argvars, 2) == FAIL) {
   return;
 }

 win_T *wp = find_win_by_nr_or_id(&argvars[0]);
 if (wp == NULL) {
   return;
 }

 bool error = false;
 linenr_T lnum = (linenr_T)tv_get_number_chk(&argvars[1], &error);
 if (error || lnum < 0 || lnum > wp->w_buffer->b_ml.ml_line_count) {
   return;
 }

 int screencol = (int)tv_get_number_chk(&argvars[2], &error);
 if (error || screencol < 0) {
   return;
 }

 rettv->vval.v_number = virtcol2col(wp, lnum, screencol);
}

/// Make sure the cursor is in the visible part of the topline after scrolling
/// the screen with 'smoothscroll'.
static void cursor_correct_sms(win_T *wp)
{
 if (!wp->w_p_sms || !wp->w_p_wrap || wp->w_cursor.lnum != wp->w_topline) {
   return;
 }

 int so = get_scrolloff_value(wp);
 int width1 = wp->w_view_width - win_col_off(wp);
 int width2 = width1 + win_col_off2(wp);
 int so_cols = so == 0 ? 0 : width1 + (so - 1) * width2;
 int space_cols = (wp->w_view_height - 1) * width2;
 int size = so == 0 ? 0 : linetabsize_eol(wp, wp->w_topline);

 if (wp->w_topline == 1 && wp->w_skipcol == 0) {
   so_cols = 0;               // Ignore 'scrolloff' at top of buffer.
 } else if (so_cols > space_cols / 2) {
   so_cols = space_cols / 2;  // Not enough room: put cursor in the middle.
 }

 // Not enough screen lines in topline: ignore 'scrolloff'.
 while (so_cols > size && so_cols - width2 >= width1 && width1 > 0) {
   so_cols -= width2;
 }
 if (so_cols >= width1 && so_cols > size) {
   so_cols -= width1;
 }

 int overlap = wp->w_skipcol == 0
               ? 0 : sms_marker_overlap(wp, wp->w_view_width - width2);
 // If we have non-zero scrolloff, ignore marker overlap.
 int top = wp->w_skipcol + (so_cols != 0 ? so_cols : overlap);
 int bot = wp->w_skipcol + width1 + (wp->w_view_height - 1) * width2 - so_cols;

 validate_virtcol(wp);
 colnr_T col = wp->w_virtcol;

 if (col < top) {
   if (col < width1) {
     col += width1;
   }
   while (width2 > 0 && col < top) {
     col += width2;
   }
 } else {
   while (width2 > 0 && col >= bot) {
     col -= width2;
   }
 }

 if (col != wp->w_virtcol) {
   wp->w_curswant = col;
   int rc = coladvance(wp, wp->w_curswant);
   // validate_virtcol() marked various things as valid, but after
   // moving the cursor they need to be recomputed
   wp->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW|VALID_VIRTCOL);
   if (rc == FAIL && wp->w_skipcol > 0
       && wp->w_cursor.lnum < wp->w_buffer->b_ml.ml_line_count) {
     validate_virtcol(wp);
     if (wp->w_virtcol < wp->w_skipcol + overlap) {
       // Cursor still not visible: move it to the next line instead.
       wp->w_cursor.lnum++;
       wp->w_cursor.col = 0;
       wp->w_cursor.coladd = 0;
       wp->w_curswant = 0;
       wp->w_valid &= ~VALID_VIRTCOL;
     }
   }
 }
}

/// Scroll "count" lines up or down, and redraw.
void scroll_redraw(int up, linenr_T count)
{
 linenr_T prev_topline = curwin->w_topline;
 int prev_skipcol = curwin->w_skipcol;
 int prev_topfill = curwin->w_topfill;
 linenr_T prev_lnum = curwin->w_cursor.lnum;

 bool moved = up
              ? scrollup(curwin, count, true)
              : scrolldown(curwin, count, true);

 if (get_scrolloff_value(curwin) > 0) {
   // Adjust the cursor position for 'scrolloff'.  Mark w_topline as
   // valid, otherwise the screen jumps back at the end of the file.
   cursor_correct(curwin);
   check_cursor_moved(curwin);
   curwin->w_valid |= VALID_TOPLINE;

   // If moved back to where we were, at least move the cursor, otherwise
   // we get stuck at one position.  Don't move the cursor up if the
   // first line of the buffer is already on the screen
   while (curwin->w_topline == prev_topline
          && curwin->w_skipcol == prev_skipcol
          && curwin->w_topfill == prev_topfill) {
     if (up) {
       if (curwin->w_cursor.lnum > prev_lnum
           || cursor_down(1L, false) == FAIL) {
         break;
       }
     } else {
       if (curwin->w_cursor.lnum < prev_lnum
           || prev_topline == 1L
           || cursor_up(1L, false) == FAIL) {
         break;
       }
     }
     // Mark w_topline as valid, otherwise the screen jumps back at the
     // end of the file.
     check_cursor_moved(curwin);
     curwin->w_valid |= VALID_TOPLINE;
   }
 }

 if (moved) {
   curwin->w_viewport_invalid = true;
 }

 cursor_correct_sms(curwin);
 if (curwin->w_cursor.lnum != prev_lnum) {
   coladvance(curwin, curwin->w_curswant);
 }
 redraw_later(curwin, UPD_VALID);
}

/// Scroll a window down by "line_count" logical lines.  "CTRL-Y"
///
/// @param line_count number of lines to scroll
/// @param byfold if true, count a closed fold as one line
bool scrolldown(win_T *wp, linenr_T line_count, int byfold)
{
 int done = 0;                // total # of physical lines done
 int width1 = 0;
 int width2 = 0;
 bool do_sms = wp->w_p_wrap && wp->w_p_sms;

 if (do_sms) {
   width1 = wp->w_view_width - win_col_off(wp);
   width2 = width1 + win_col_off2(wp);
 }

 // Make sure w_topline is at the first of a sequence of folded lines.
 hasFolding(wp, wp->w_topline, &wp->w_topline, NULL);
 validate_cursor(wp);            // w_wrow needs to be valid
 for (int todo = line_count; todo > 0; todo--) {
   bool can_fill = wp->w_topfill < wp->w_view_height - 1
                   && wp->w_topfill < win_get_fill(wp, wp->w_topline);
   // break when at the very top
   if (wp->w_topline == 1 && !can_fill && (!do_sms || wp->w_skipcol < width1)) {
     break;
   }
   if (do_sms && wp->w_skipcol >= width1) {
     // scroll a screen line down
     if (wp->w_skipcol >= width1 + width2) {
       wp->w_skipcol -= width2;
     } else {
       wp->w_skipcol -= width1;
     }
     redraw_later(wp, UPD_NOT_VALID);
     done++;
   } else if (can_fill) {
     wp->w_topfill++;
     done++;
   } else {
     // scroll a text line down
     wp->w_topline--;
     wp->w_skipcol = 0;
     wp->w_topfill = 0;
     // A sequence of folded lines only counts for one logical line
     linenr_T first;
     if (hasFolding(wp, wp->w_topline, &first, NULL)) {
       done += !decor_conceal_line(wp, first - 1, false);
       if (!byfold) {
         todo -= wp->w_topline - first - 1;
       }
       wp->w_botline -= wp->w_topline - first;
       wp->w_topline = first;
     } else if (decor_conceal_line(wp, wp->w_topline - 1, false)) {
       todo++;
     } else {
       if (do_sms) {
         int size = linetabsize_eol(wp, wp->w_topline);
         if (size > width1) {
           wp->w_skipcol = width1;
           size -= width1;
           redraw_later(wp, UPD_NOT_VALID);
         }
         while (size > width2) {
           wp->w_skipcol += width2;
           size -= width2;
         }
         done++;
       } else {
         done += plines_win_nofill(wp, wp->w_topline, true);
       }
     }
   }
   wp->w_botline--;                // approximate w_botline
   invalidate_botline_win(wp);
 }

 // Adjust for concealed lines above w_topline
 while (wp->w_topline > 1 && decor_conceal_line(wp, wp->w_topline - 2, false)) {
   wp->w_topline--;
   hasFolding(wp, wp->w_topline, &wp->w_topline, NULL);
 }

 wp->w_wrow += done;               // keep w_wrow updated
 wp->w_cline_row += done;          // keep w_cline_row updated

 if (wp->w_cursor.lnum == wp->w_topline) {
   wp->w_cline_row = 0;
 }
 check_topfill(wp, true);

 // Compute the row number of the last row of the cursor line
 // and move the cursor onto the displayed part of the window.
 int wrow = wp->w_wrow;
 if (wp->w_p_wrap && wp->w_view_width != 0) {
   validate_virtcol(wp);
   validate_cheight(wp);
   wrow += wp->w_cline_height - 1 -
           wp->w_virtcol / wp->w_view_width;
 }
 bool moved = false;
 while (wrow >= wp->w_view_height && wp->w_cursor.lnum > 1) {
   linenr_T first;
   if (hasFolding(wp, wp->w_cursor.lnum, &first, NULL)) {
     wrow -= !decor_conceal_line(wp, wp->w_cursor.lnum - 1, false);
     wp->w_cursor.lnum = MAX(first - 1, 1);
   } else {
     wrow -= plines_win(wp, wp->w_cursor.lnum--, true);
   }
   wp->w_valid &=
     ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW|VALID_VIRTCOL);
   moved = true;
 }
 if (moved) {
   // Move cursor to first line of closed fold.
   foldAdjustCursor(wp);
   coladvance(wp, wp->w_curswant);
 }
 wp->w_cursor.lnum = MAX(wp->w_cursor.lnum, wp->w_topline);

 return moved;
}

/// Scroll a window up by "line_count" logical lines.  "CTRL-E"
///
/// @param line_count number of lines to scroll
/// @param byfold if true, count a closed fold as one line
bool scrollup(win_T *wp, linenr_T line_count, bool byfold)
{
 linenr_T topline = wp->w_topline;
 linenr_T botline = wp->w_botline;
 bool do_sms = wp->w_p_wrap && wp->w_p_sms;

 if (do_sms || (byfold && win_lines_concealed(wp)) || win_may_fill(wp)) {
   int width1 = wp->w_view_width - win_col_off(wp);
   int width2 = width1 + win_col_off2(wp);
   int size = 0;
   const colnr_T prev_skipcol = wp->w_skipcol;

   if (do_sms) {
     size = linetabsize_eol(wp, wp->w_topline);
   }

   // diff mode: first consume "topfill"
   // 'smoothscroll': increase "w_skipcol" until it goes over the end of
   // the line, then advance to the next line.
   // folding: count each sequence of folded lines as one logical line.
   for (int todo = line_count; todo > 0; todo--) {
     todo += decor_conceal_line(wp, wp->w_topline - 1, false);
     if (wp->w_topfill > 0) {
       wp->w_topfill--;
     } else {
       linenr_T lnum = wp->w_topline;
       if (byfold) {
         // for a closed fold: go to the last line in the fold
         hasFolding(wp, lnum, NULL, &lnum);
       }
       if (lnum == wp->w_topline && do_sms) {
         // 'smoothscroll': increase "w_skipcol" until it goes over
         // the end of the line, then advance to the next line.
         int add = wp->w_skipcol > 0 ? width2 : width1;
         wp->w_skipcol += add;
         if (wp->w_skipcol >= size) {
           if (lnum == wp->w_buffer->b_ml.ml_line_count) {
             // at the last screen line, can't scroll further
             wp->w_skipcol -= add;
             break;
           }
           lnum++;
         }
       } else {
         if (lnum >= wp->w_buffer->b_ml.ml_line_count) {
           break;
         }
         lnum++;
       }

       if (lnum > wp->w_topline) {
         // approximate w_botline
         wp->w_botline += lnum - wp->w_topline;
         wp->w_topline = lnum;
         wp->w_topfill = win_get_fill(wp, lnum);
         wp->w_skipcol = 0;
         if (todo > 1 && do_sms) {
           size = linetabsize_eol(wp, wp->w_topline);
         }
       }
     }
   }

   if (prev_skipcol > 0 || wp->w_skipcol > 0) {
     // need to redraw more, because wl_size of the (new) topline may
     // now be invalid
     redraw_later(wp, UPD_NOT_VALID);
   }
 } else {
   wp->w_topline += line_count;
   wp->w_botline += line_count;            // approximate w_botline
 }

 wp->w_topline = MIN(wp->w_topline, wp->w_buffer->b_ml.ml_line_count);
 wp->w_botline = MIN(wp->w_botline, wp->w_buffer->b_ml.ml_line_count + 1);

 check_topfill(wp, false);

 // Make sure w_topline is at the first of a sequence of folded lines.
 hasFolding(wp, wp->w_topline, &wp->w_topline, NULL);

 wp->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE);
 if (wp->w_cursor.lnum < wp->w_topline) {
   wp->w_cursor.lnum = wp->w_topline;
   wp->w_valid &=
     ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW|VALID_VIRTCOL);
   coladvance(wp, wp->w_curswant);
 }

 bool moved = topline != wp->w_topline || botline != wp->w_botline;

 return moved;
}

/// Called after changing the cursor column: make sure that curwin->w_skipcol is
/// valid for 'smoothscroll'.
void adjust_skipcol(void)
{
 if (!curwin->w_p_wrap || !curwin->w_p_sms || curwin->w_cursor.lnum != curwin->w_topline) {
   return;
 }

 int width1 = curwin->w_view_width - win_col_off(curwin);
 if (width1 <= 0) {
   return;  // no text will be displayed
 }
 int width2 = width1 + win_col_off2(curwin);
 int so = get_scrolloff_value(curwin);
 colnr_T scrolloff_cols = so == 0 ? 0 : width1 + (so - 1) * width2;
 bool scrolled = false;

 validate_cheight(curwin);
 if (curwin->w_cline_height == curwin->w_view_height
     // w_cline_height may be capped at w_view_height, check there aren't
     // actually more lines.
     && plines_win(curwin, curwin->w_cursor.lnum, false) <= curwin->w_view_height) {
   // the line just fits in the window, don't scroll
   reset_skipcol(curwin);
   return;
 }

 validate_virtcol(curwin);
 int overlap = sms_marker_overlap(curwin, curwin->w_view_width - width2);
 while (curwin->w_skipcol > 0
        && curwin->w_virtcol < curwin->w_skipcol + overlap + scrolloff_cols) {
   // scroll a screen line down
   if (curwin->w_skipcol >= width1 + width2) {
     curwin->w_skipcol -= width2;
   } else {
     curwin->w_skipcol -= width1;
   }
   scrolled = true;
 }
 if (scrolled) {
   validate_virtcol(curwin);
   redraw_later(curwin, UPD_NOT_VALID);
   return;  // don't scroll in the other direction now
 }
 int row = 0;
 colnr_T col = curwin->w_virtcol + scrolloff_cols;

 // Avoid adjusting for 'scrolloff' beyond the text line height.
 if (scrolloff_cols > 0) {
   int size = linetabsize_eol(curwin, curwin->w_topline);
   size = width1 + width2 * ((size - width1 + width2 - 1) / width2);
   while (col > size) {
     col -= width2;
   }
 }
 col -= curwin->w_skipcol;

 if (col >= width1) {
   col -= width1;
   row++;
 }
 if (col > width2) {
   row += (int)col / width2;
 }
 if (row >= curwin->w_view_height) {
   if (curwin->w_skipcol == 0) {
     curwin->w_skipcol += width1;
     row--;
   }
   if (row >= curwin->w_view_height) {
     curwin->w_skipcol += (row - curwin->w_view_height) * width2;
   }
   redraw_later(curwin, UPD_NOT_VALID);
 }
}

/// Don't end up with too many filler lines in the window.
///
/// @param down  when true scroll down when not enough space
void check_topfill(win_T *wp, bool down)
{
 if (wp->w_topfill > 0) {
   int n = plines_win_nofill(wp, wp->w_topline, true);
   if (wp->w_topfill + n > wp->w_view_height) {
     if (down && wp->w_topline > 1) {
       wp->w_topline--;
       wp->w_topfill = 0;
     } else {
       wp->w_topfill = wp->w_view_height - n;
       wp->w_topfill = MAX(wp->w_topfill, 0);
     }
   }
 }
 win_check_anchored_floats(wp);
}

// Scroll the screen one line down, but don't do it if it would move the
// cursor off the screen.
void scrolldown_clamp(void)
{
 bool can_fill = (curwin->w_topfill < win_get_fill(curwin, curwin->w_topline));

 if (curwin->w_topline <= 1
     && !can_fill) {
   return;
 }

 validate_cursor(curwin);        // w_wrow needs to be valid

 // Compute the row number of the last row of the cursor line
 // and make sure it doesn't go off the screen. Make sure the cursor
 // doesn't go past 'scrolloff' lines from the screen end.
 int end_row = curwin->w_wrow;
 if (can_fill) {
   end_row++;
 } else {
   end_row += plines_win_nofill(curwin, curwin->w_topline - 1, true);
 }
 if (curwin->w_p_wrap && curwin->w_view_width != 0) {
   validate_cheight(curwin);
   validate_virtcol(curwin);
   end_row += curwin->w_cline_height - 1 -
              curwin->w_virtcol / curwin->w_view_width;
 }
 if (end_row < curwin->w_view_height - get_scrolloff_value(curwin)) {
   if (can_fill) {
     curwin->w_topfill++;
     check_topfill(curwin, true);
   } else {
     curwin->w_topline--;
     curwin->w_topfill = 0;
   }
   hasFolding(curwin, curwin->w_topline, &curwin->w_topline, NULL);
   curwin->w_botline--;            // approximate w_botline
   curwin->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE);
 }
}

// Scroll the screen one line up, but don't do it if it would move the cursor
// off the screen.
void scrollup_clamp(void)
{
 if (curwin->w_topline == curbuf->b_ml.ml_line_count
     && curwin->w_topfill == 0) {
   return;
 }

 validate_cursor(curwin);        // w_wrow needs to be valid

 // Compute the row number of the first row of the cursor line
 // and make sure it doesn't go off the screen. Make sure the cursor
 // doesn't go before 'scrolloff' lines from the screen start.
 int start_row = (curwin->w_wrow
                  - plines_win_nofill(curwin, curwin->w_topline, true)
                  - curwin->w_topfill);
 if (curwin->w_p_wrap && curwin->w_view_width != 0) {
   validate_virtcol(curwin);
   start_row -= curwin->w_virtcol / curwin->w_view_width;
 }
 if (start_row >= get_scrolloff_value(curwin)) {
   if (curwin->w_topfill > 0) {
     curwin->w_topfill--;
   } else {
     hasFolding(curwin, curwin->w_topline, NULL, &curwin->w_topline);
     curwin->w_topline++;
   }
   curwin->w_botline++;                // approximate w_botline
   curwin->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE);
 }
}

// Add one line above "lp->lnum".  This can be a filler line, a closed fold or
// a (wrapped) text line.  Uses and sets "lp->fill".
// Returns the height of the added line in "lp->height".
// Lines above the first one are incredibly high: MAXCOL.
// When "winheight" is true limit to window height.
static void topline_back_winheight(win_T *wp, lineoff_T *lp, int winheight)
{
 if (lp->fill < win_get_fill(wp, lp->lnum)) {
   // Add a filler line
   lp->fill++;
   lp->height = 1;
 } else {
   lp->lnum--;
   lp->fill = 0;
   if (lp->lnum < 1) {
     lp->height = MAXCOL;
   } else if (hasFolding(wp, lp->lnum, &lp->lnum, NULL)) {
     // Add a closed fold unless concealed.
     lp->height = !decor_conceal_line(wp, lp->lnum - 1, false);
   } else {
     lp->height = plines_win_nofill(wp, lp->lnum, winheight);
   }
 }
}

static void topline_back(win_T *wp, lineoff_T *lp)
{
 topline_back_winheight(wp, lp, true);
}

// Add one line below "lp->lnum".  This can be a filler line, a closed fold or
// a (wrapped) text line.  Uses and sets "lp->fill".
// Returns the height of the added line in "lp->height".
// Lines below the last one are incredibly high.
static void botline_forw(win_T *wp, lineoff_T *lp)
{
 if (lp->fill < win_get_fill(wp, lp->lnum + 1)) {
   // Add a filler line.
   lp->fill++;
   lp->height = 1;
 } else {
   lp->lnum++;
   lp->fill = 0;
   assert(wp->w_buffer != 0);
   if (lp->lnum > wp->w_buffer->b_ml.ml_line_count) {
     lp->height = MAXCOL;
   } else if (hasFolding(wp, lp->lnum, NULL, &lp->lnum)) {
     // Add a closed fold unless concealed.
     lp->height = !decor_conceal_line(wp, lp->lnum - 1, false);
   } else {
     lp->height = plines_win_nofill(wp, lp->lnum, true);
   }
 }
}

// Recompute topline to put the cursor at the top of the window.
// Scroll at least "min_scroll" lines.
// If "always" is true, always set topline (for "zt").
void scroll_cursor_top(win_T *wp, int min_scroll, int always)
{
 linenr_T old_topline = wp->w_topline;
 int old_skipcol = wp->w_skipcol;
 linenr_T old_topfill = wp->w_topfill;
 int off = get_scrolloff_value(wp);

 if (mouse_dragging > 0) {
   off = mouse_dragging - 1;
 }

 // Decrease topline until:
 // - it has become 1
 // - (part of) the cursor line is moved off the screen or
 // - moved at least 'scrolljump' lines and
 // - at least 'scrolloff' lines above and below the cursor
 validate_cheight(wp);
 int scrolled = 0;
 int used = wp->w_cline_height;  // includes filler lines above
 if (wp->w_cursor.lnum < wp->w_topline) {
   scrolled = used;
 }

 linenr_T top;  // just above displayed lines
 linenr_T bot;  // just below displayed lines
 if (hasFolding(wp, wp->w_cursor.lnum, &top, &bot)) {
   top--;
   bot++;
 } else {
   top = wp->w_cursor.lnum - 1;
   bot = wp->w_cursor.lnum + 1;
 }
 linenr_T new_topline = top + 1;

 // "used" already contains the number of filler lines above, don't add it
 // again.
 // Hide filler lines above cursor line by adding them to "extra".
 int extra = win_get_fill(wp, wp->w_cursor.lnum);

 // Check if the lines from "top" to "bot" fit in the window.  If they do,
 // set new_topline and advance "top" and "bot" to include more lines.
 while (top > 0) {
   int i = plines_win_nofill(wp, top, true);
   hasFolding(wp, top, &top, NULL);
   if (top < wp->w_topline) {
     scrolled += i;
   }

   // If scrolling is needed, scroll at least 'sj' lines.
   if ((new_topline >= wp->w_topline || scrolled > min_scroll) && extra >= off) {
     break;
   }

   used += i;
   if (extra + i <= off && bot < wp->w_buffer->b_ml.ml_line_count) {
     used += plines_win_full(wp, bot, &bot, NULL, true, true);
   }
   if (used > wp->w_view_height) {
     break;
   }

   extra += i;
   new_topline = top;
   top--;
   bot++;
 }

 // If we don't have enough space, put cursor in the middle.
 // This makes sure we get the same position when using "k" and "j"
 // in a small window.
 if (used > wp->w_view_height) {
   scroll_cursor_halfway(wp, false, false);
 } else {
   // If "always" is false, only adjust topline to a lower value, higher
   // value may happen with wrapping lines.
   if (new_topline < wp->w_topline || always) {
     wp->w_topline = new_topline;
   }
   wp->w_topline = MIN(wp->w_topline, wp->w_cursor.lnum);
   wp->w_topfill = win_get_fill(wp, wp->w_topline);
   if (wp->w_topfill > 0 && extra > off) {
     wp->w_topfill -= extra - off;
     wp->w_topfill = MAX(wp->w_topfill, 0);
   }
   check_topfill(wp, false);
   if (wp->w_topline != old_topline) {
     reset_skipcol(wp);
   } else if (wp->w_topline == wp->w_cursor.lnum) {
     validate_virtcol(wp);
     if (wp->w_skipcol >= wp->w_virtcol) {
       // TODO(vim): if the line doesn't fit may optimize w_skipcol instead
       // of making it zero
       reset_skipcol(wp);
     }
   }
   if (wp->w_topline != old_topline
       || wp->w_skipcol != old_skipcol
       || wp->w_topfill != old_topfill) {
     wp->w_valid &=
       ~(VALID_WROW|VALID_CROW|VALID_BOTLINE|VALID_BOTLINE_AP);
   }
   wp->w_valid |= VALID_TOPLINE;
   wp->w_viewport_invalid = true;
 }
}

// Set w_empty_rows and w_filler_rows for window "wp", having used up "used"
// screen lines for text lines.
void set_empty_rows(win_T *wp, int used)
{
 wp->w_filler_rows = 0;
 if (used == 0) {
   wp->w_empty_rows = 0;  // single line that doesn't fit
 } else {
   wp->w_empty_rows = wp->w_view_height - used;
   if (wp->w_botline <= wp->w_buffer->b_ml.ml_line_count) {
     wp->w_filler_rows = win_get_fill(wp, wp->w_botline);
     if (wp->w_empty_rows > wp->w_filler_rows) {
       wp->w_empty_rows -= wp->w_filler_rows;
     } else {
       wp->w_filler_rows = wp->w_empty_rows;
       wp->w_empty_rows = 0;
     }
   }
 }
}

/// Recompute topline to put the cursor at the bottom of the window.
/// When scrolling scroll at least "min_scroll" lines.
/// If "set_topbot" is true, set topline and botline first (for "zb").
/// This is messy stuff!!!
void scroll_cursor_bot(win_T *wp, int min_scroll, bool set_topbot)
{
 lineoff_T loff;
 linenr_T old_topline = wp->w_topline;
 int old_skipcol = wp->w_skipcol;
 int old_topfill = wp->w_topfill;
 linenr_T old_botline = wp->w_botline;
 int old_valid = wp->w_valid;
 int old_empty_rows = wp->w_empty_rows;
 linenr_T cln = wp->w_cursor.lnum;  // Cursor Line Number
 bool do_sms = wp->w_p_wrap && wp->w_p_sms;

 if (set_topbot) {
   int used = 0;
   wp->w_botline = cln + 1;
   loff.lnum = cln + 1;
   loff.fill = 0;
   while (true) {
     topline_back_winheight(wp, &loff, false);
     if (loff.height == MAXCOL) {
       break;
     }
     if (used + loff.height > wp->w_view_height) {
       if (do_sms) {
         // 'smoothscroll' and 'wrap' are set.  The above line is
         // too long to show in its entirety, so we show just a part
         // of it.
         if (used < wp->w_view_height) {
           int plines_offset = used + loff.height - wp->w_view_height;
           used = wp->w_view_height;
           wp->w_topfill = loff.fill;
           wp->w_topline = loff.lnum;
           wp->w_skipcol = skipcol_from_plines(wp, plines_offset);
         }
       }
       break;
     }
     wp->w_topfill = loff.fill;
     wp->w_topline = loff.lnum;
     used += loff.height;
   }

   set_empty_rows(wp, used);
   wp->w_valid |= VALID_BOTLINE|VALID_BOTLINE_AP;
   if (wp->w_topline != old_topline
       || wp->w_topfill != old_topfill
       || wp->w_skipcol != old_skipcol
       || wp->w_skipcol != 0) {
     wp->w_valid &= ~(VALID_WROW|VALID_CROW);
     if (wp->w_skipcol != old_skipcol) {
       redraw_later(wp, UPD_NOT_VALID);
     } else {
       reset_skipcol(wp);
     }
   }
 } else {
   validate_botline_win(wp);
 }

 // The lines of the cursor line itself are always used.
 int used = plines_win_nofill(wp, cln, true);

 int scrolled = 0;
 // If the cursor is on or below botline, we will at least scroll by the
 // height of the cursor line, which is "used".  Correct for empty lines,
 // which are really part of botline.
 if (cln >= wp->w_botline) {
   scrolled = used;
   if (cln == wp->w_botline) {
     scrolled -= wp->w_empty_rows;
   }
   if (do_sms) {
     // 'smoothscroll' and 'wrap' are set.
     // Calculate how many screen lines the current top line of window
     // occupies. If it is occupying more than the entire window, we
     // need to scroll the additional clipped lines to scroll past the
     // top line before we can move on to the other lines.
     int top_plines = plines_win_nofill(wp, wp->w_topline, false);
     int width1 = wp->w_view_width - win_col_off(wp);

     if (width1 > 0) {
       int width2 = width1 + win_col_off2(wp);
       int skip_lines = 0;

       // A similar formula is used in curs_columns().
       if (wp->w_skipcol > width1) {
         skip_lines += (wp->w_skipcol - width1) / width2 + 1;
       } else if (wp->w_skipcol > 0) {
         skip_lines = 1;
       }

       top_plines -= skip_lines;
       if (top_plines > wp->w_view_height) {
         scrolled += (top_plines - wp->w_view_height);
       }
     }
   }
 }

 lineoff_T boff;
 // Stop counting lines to scroll when
 // - hitting start of the file
 // - scrolled nothing or at least 'sj' lines
 // - at least 'so' lines below the cursor
 // - lines between botline and cursor have been counted
 if (!hasFolding(wp, wp->w_cursor.lnum, &loff.lnum, &boff.lnum)) {
   loff.lnum = cln;
   boff.lnum = cln;
 }
 loff.fill = 0;
 boff.fill = 0;
 int fill_below_window = win_get_fill(wp, wp->w_botline) - wp->w_filler_rows;

 int extra = 0;
 int so = get_scrolloff_value(wp);
 while (loff.lnum > 1) {
   // Stop when scrolled nothing or at least "min_scroll", found "extra"
   // context for 'scrolloff' and counted all lines below the window.
   if ((((scrolled <= 0 || scrolled >= min_scroll)
         && extra >= (mouse_dragging > 0 ? mouse_dragging - 1 : so))
        || boff.lnum + 1 > wp->w_buffer->b_ml.ml_line_count)
       && loff.lnum <= wp->w_botline
       && (loff.lnum < wp->w_botline
           || loff.fill >= fill_below_window)) {
     break;
   }

   // Add one line above
   topline_back(wp, &loff);
   if (loff.height == MAXCOL) {
     used = MAXCOL;
   } else {
     used += loff.height;
   }
   if (used > wp->w_view_height) {
     break;
   }
   if (loff.lnum >= wp->w_botline
       && (loff.lnum > wp->w_botline
           || loff.fill <= fill_below_window)) {
     // Count screen lines that are below the window.
     scrolled += loff.height;
     if (loff.lnum == wp->w_botline
         && loff.fill == 0) {
       scrolled -= wp->w_empty_rows;
     }
   }

   if (boff.lnum < wp->w_buffer->b_ml.ml_line_count) {
     // Add one line below
     botline_forw(wp, &boff);
     used += boff.height;
     if (used > wp->w_view_height) {
       break;
     }
     if (extra < (mouse_dragging > 0 ? mouse_dragging - 1 : so)
         || scrolled < min_scroll) {
       extra += boff.height;
       if (boff.lnum >= wp->w_botline
           || (boff.lnum + 1 == wp->w_botline
               && boff.fill > wp->w_filler_rows)) {
         // Count screen lines that are below the window.
         scrolled += boff.height;
         if (boff.lnum == wp->w_botline
             && boff.fill == 0) {
           scrolled -= wp->w_empty_rows;
         }
       }
     }
   }
 }

 linenr_T line_count;
 // wp->w_empty_rows is larger, no need to scroll
 if (scrolled <= 0) {
   line_count = 0;
   // more than a screenfull, don't scroll but redraw
 } else if (used > wp->w_view_height) {
   line_count = used;
   // scroll minimal number of lines
 } else {
   line_count = 0;
   boff.fill = wp->w_topfill;
   boff.lnum = wp->w_topline - 1;
   int i;
   for (i = 0; i < scrolled && boff.lnum < wp->w_botline;) {
     botline_forw(wp, &boff);
     i += boff.height;
     line_count++;
   }
   if (i < scrolled) {         // below wp->w_botline, don't scroll
     line_count = 9999;
   }
 }

 // Scroll up if the cursor is off the bottom of the screen a bit.
 // Otherwise put it at 1/2 of the screen.
 if (line_count >= wp->w_view_height && line_count > min_scroll) {
   scroll_cursor_halfway(wp, false, true);
 } else if (line_count > 0) {
   if (do_sms) {
     scrollup(wp, scrolled, true);  // TODO(vim):
   } else {
     scrollup(wp, line_count, true);
   }
 }

 // If topline didn't change we need to restore w_botline and w_empty_rows
 // (we changed them).
 // If topline did change, update_screen() will set botline.
 if (wp->w_topline == old_topline && wp->w_skipcol == old_skipcol && set_topbot) {
   wp->w_botline = old_botline;
   wp->w_empty_rows = old_empty_rows;
   wp->w_valid = old_valid;
 }
 wp->w_valid |= VALID_TOPLINE;
 wp->w_viewport_invalid = true;

 // Make sure cursor is still visible after adjusting skipcol for "zb".
 if (set_topbot) {
   cursor_correct_sms(wp);
 }
}

/// Recompute topline to put the cursor halfway across the window
///
/// @param atend if true, also put the cursor halfway to the end of the file.
///
void scroll_cursor_halfway(win_T *wp, bool atend, bool prefer_above)
{
 linenr_T old_topline = wp->w_topline;
 lineoff_T loff = { .lnum = wp->w_cursor.lnum };
 lineoff_T boff = { .lnum = wp->w_cursor.lnum };
 hasFolding(wp, loff.lnum, &loff.lnum, &boff.lnum);
 int used = plines_win_nofill(wp, loff.lnum, true);
 loff.fill = 0;
 boff.fill = 0;
 linenr_T topline = loff.lnum;
 colnr_T skipcol = 0;

 int want_height;
 bool do_sms = wp->w_p_wrap && wp->w_p_sms;
 if (do_sms) {
   // 'smoothscroll' and 'wrap' are set
   if (atend) {
     want_height = (wp->w_view_height - used) / 2;
     used = 0;
   } else {
     want_height = wp->w_view_height;
   }
 }

 int topfill = 0;
 while (topline > 1) {
   // If using smoothscroll, we can precisely scroll to the
   // exact point where the cursor is halfway down the screen.
   if (do_sms) {
     topline_back_winheight(wp, &loff, false);
     if (loff.height == MAXCOL) {
       break;
     }
     used += loff.height;
     if (!atend && boff.lnum < wp->w_buffer->b_ml.ml_line_count) {
       botline_forw(wp, &boff);
       used += boff.height;
     }
     if (used > want_height) {
       if (used - loff.height < want_height) {
         topline = loff.lnum;
         topfill = loff.fill;
         skipcol = skipcol_from_plines(wp, used - want_height);
       }
       break;
     }
     topline = loff.lnum;
     topfill = loff.fill;
     continue;
   }

   // If not using smoothscroll, we have to iteratively find how many
   // lines to scroll down to roughly fit the cursor.
   // This may not be right in the middle if the lines'
   // physical height > 1 (e.g. 'wrap' is on).

   // Depending on "prefer_above" we add a line above or below first.
   // Loop twice to avoid duplicating code.
   bool done = false;
   int above = 0;
   int below = 0;
   for (int round = 1; round <= 2; round++) {
     if (prefer_above
         ? (round == 2 && below < above)
         : (round == 1 && below <= above)) {
       // add a line below the cursor
       if (boff.lnum < wp->w_buffer->b_ml.ml_line_count) {
         botline_forw(wp, &boff);
         used += boff.height;
         if (used > wp->w_view_height) {
           done = true;
           break;
         }
         below += boff.height;
       } else {
         below++;                    // count a "~" line
         if (atend) {
           used++;
         }
       }
     }

     if (prefer_above
         ? (round == 1 && below >= above)
         : (round == 1 && below > above)) {
       // add a line above the cursor
       topline_back(wp, &loff);
       if (loff.height == MAXCOL) {
         used = MAXCOL;
       } else {
         used += loff.height;
       }
       if (used > wp->w_view_height) {
         done = true;
         break;
       }
       above += loff.height;
       topline = loff.lnum;
       topfill = loff.fill;
     }
   }
   if (done) {
     break;
   }
 }

 if (!hasFolding(wp, topline, &wp->w_topline, NULL)
     && (wp->w_topline != topline || skipcol != 0 || wp->w_skipcol != 0)) {
   wp->w_topline = topline;
   if (skipcol != 0) {
     wp->w_skipcol = skipcol;
     redraw_later(wp, UPD_NOT_VALID);
   } else if (do_sms) {
     reset_skipcol(wp);
   }
 }
 wp->w_topfill = topfill;
 if (old_topline > wp->w_topline + wp->w_view_height) {
   wp->w_botfill = false;
 }
 check_topfill(wp, false);
 wp->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE|VALID_BOTLINE_AP);
 wp->w_valid |= VALID_TOPLINE;
}

// Correct the cursor position so that it is in a part of the screen at least
// 'so' lines from the top and bottom, if possible.
// If not possible, put it at the same position as scroll_cursor_halfway().
// When called topline must be valid!
void cursor_correct(win_T *wp)
{
 // How many lines we would like to have above/below the cursor depends on
 // whether the first/last line of the file is on screen.
 int above_wanted = get_scrolloff_value(wp);
 int below_wanted = get_scrolloff_value(wp);
 if (mouse_dragging > 0) {
   above_wanted = mouse_dragging - 1;
   below_wanted = mouse_dragging - 1;
 }
 if (wp->w_topline == 1) {
   above_wanted = 0;
   int max_off = wp->w_view_height / 2;
   below_wanted = MIN(below_wanted, max_off);
 }
 validate_botline_win(wp);
 if (wp->w_botline == wp->w_buffer->b_ml.ml_line_count + 1
     && mouse_dragging == 0) {
   below_wanted = 0;
   int max_off = (wp->w_view_height - 1) / 2;
   above_wanted = MIN(above_wanted, max_off);
 }

 // If there are sufficient file-lines above and below the cursor, we can
 // return now.
 linenr_T cln = wp->w_cursor.lnum;  // Cursor Line Number
 if (cln >= wp->w_topline + above_wanted
     && cln < wp->w_botline - below_wanted
     && !win_lines_concealed(wp)) {
   return;
 }

 if (wp->w_p_sms && !wp->w_p_wrap) {
   // 'smoothscroll' is active
   if (wp->w_cline_height == wp->w_view_height) {
     // The cursor line just fits in the window, don't scroll.
     reset_skipcol(wp);
     return;
   }
   // TODO(vim): If the cursor line doesn't fit in the window then only adjust w_skipcol.
 }

 // Narrow down the area where the cursor can be put by taking lines from
 // the top and the bottom until:
 // - the desired context lines are found
 // - the lines from the top is past the lines from the bottom
 linenr_T topline = wp->w_topline;
 linenr_T botline = wp->w_botline - 1;
 // count filler lines as context
 int above = wp->w_topfill;  // screen lines above topline
 int below = wp->w_filler_rows;  // screen lines below botline
 while ((above < above_wanted || below < below_wanted) && topline < botline) {
   if (below < below_wanted && (below <= above || above >= above_wanted)) {
     below += plines_win_full(wp, botline, NULL, NULL, true, true);
     hasFolding(wp, botline, &botline, NULL);
     botline--;
   }
   if (above < above_wanted && (above < below || below >= below_wanted)) {
     above += plines_win_nofill(wp, topline, true);
     hasFolding(wp, topline, NULL, &topline);

     // Count filler lines below this line as context.
     if (topline < botline) {
       above += win_get_fill(wp, topline + 1);
     }
     topline++;
   }
 }
 if (topline == botline || botline == 0) {
   wp->w_cursor.lnum = topline;
 } else if (topline > botline) {
   wp->w_cursor.lnum = botline;
 } else {
   if (cln < topline && wp->w_topline > 1) {
     wp->w_cursor.lnum = topline;
     wp->w_valid &=
       ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW);
   }
   if (cln > botline && wp->w_botline <= wp->w_buffer->b_ml.ml_line_count) {
     wp->w_cursor.lnum = botline;
     wp->w_valid &=
       ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW);
   }
 }
 check_cursor_moved(wp);
 wp->w_valid |= VALID_TOPLINE;
 wp->w_viewport_invalid = true;
}

/// Decide how much overlap to use for page-up or page-down scrolling.
/// This is symmetric, so that doing both keeps the same lines displayed.
/// Three lines are examined:
///
///  before CTRL-F          after CTRL-F / before CTRL-B
///     etc.                    l1
///  l1 last but one line       ------------
///  l2 last text line          l2 top text line
///  -------------              l3 second text line
///  l3                            etc.
static int get_scroll_overlap(Direction dir)
{
 lineoff_T loff;
 int min_height = curwin->w_view_height - 2;

 validate_botline_win(curwin);
 if ((dir == BACKWARD && curwin->w_topline == 1)
     || (dir == FORWARD && curwin->w_botline > curbuf->b_ml.ml_line_count)) {
   return min_height + 2;  // no overlap, still handle 'smoothscroll'
 }

 loff.lnum = dir == FORWARD ? curwin->w_botline : curwin->w_topline - 1;
 loff.fill = win_get_fill(curwin, loff.lnum + (dir == BACKWARD))
             - (dir == FORWARD ? curwin->w_filler_rows : curwin->w_topfill);
 loff.height = loff.fill > 0 ? 1 : plines_win_nofill(curwin, loff.lnum, true);

 int h1 = loff.height;
 if (h1 > min_height) {
   return min_height + 2;  // no overlap
 }
 if (dir == FORWARD) {
   topline_back(curwin, &loff);
 } else {
   botline_forw(curwin, &loff);
 }

 int h2 = loff.height;
 if (h2 == MAXCOL || h2 + h1 > min_height) {
   return min_height + 2;  // no overlap
 }
 if (dir == FORWARD) {
   topline_back(curwin, &loff);
 } else {
   botline_forw(curwin, &loff);
 }

 int h3 = loff.height;
 if (h3 == MAXCOL || h3 + h2 > min_height) {
   return min_height + 2;  // no overlap
 }
 if (dir == FORWARD) {
   topline_back(curwin, &loff);
 } else {
   botline_forw(curwin, &loff);
 }

 int h4 = loff.height;
 if (h4 == MAXCOL || h4 + h3 + h2 > min_height || h3 + h2 + h1 > min_height) {
   return min_height + 1;  // 1 line overlap
 } else {
   return min_height;      // 2 lines overlap
 }
}

/// Scroll "count" lines with 'smoothscroll' in direction "dir". Return true
/// when scrolling happened. Adjust "curscount" for scrolling different amount
/// of lines when 'smoothscroll' is disabled.
static bool scroll_with_sms(Direction dir, int count, int *curscount)
{
 int prev_sms = curwin->w_p_sms;
 colnr_T prev_skipcol = curwin->w_skipcol;
 linenr_T prev_topline = curwin->w_topline;
 int prev_topfill = curwin->w_topfill;

 curwin->w_p_sms = true;
 scroll_redraw(dir == FORWARD, count);

 // Not actually smoothscrolling but ended up with partially visible line.
 // Continue scrolling until skipcol is zero.
 if (!prev_sms && curwin->w_skipcol > 0) {
   int fixdir = dir;
   // Reverse the scroll direction when topline already changed. One line
   // extra for scrolling backward so that consuming skipcol is symmetric.
   if (labs(curwin->w_topline - prev_topline) > (dir == BACKWARD)) {
     fixdir = dir * -1;
   }

   int width1 = curwin->w_view_width - win_col_off(curwin);
   int width2 = width1 + win_col_off2(curwin);
   count = 1 + (curwin->w_skipcol - width1 - 1) / width2;
   if (fixdir == FORWARD) {
     count = 1 + (linetabsize_eol(curwin, curwin->w_topline)
                  - curwin->w_skipcol - width1 + width2 - 1) / width2;
   }
   scroll_redraw(fixdir == FORWARD, count);
   *curscount += count * (fixdir == dir ? 1 : -1);
 }
 curwin->w_p_sms = prev_sms;

 return curwin->w_topline != prev_topline
        || curwin->w_topfill != prev_topfill
        || curwin->w_skipcol != prev_skipcol;
}

/// Move screen "count" (half) pages up ("dir" is BACKWARD) or down ("dir" is
/// FORWARD) and update the screen. Handle moving the cursor and not scrolling
/// to reveal end of buffer lines for half-page scrolling with CTRL-D and CTRL-U.
///
/// @return  FAIL for failure, OK otherwise.
int pagescroll(Direction dir, int count, bool half)
{
 bool did_move = false;
 int buflen = curbuf->b_ml.ml_line_count;
 colnr_T prev_col = curwin->w_cursor.col;
 colnr_T prev_curswant = curwin->w_curswant;
 linenr_T prev_lnum = curwin->w_cursor.lnum;
 oparg_T oa = { 0 };
 cmdarg_T ca = { 0 };
 ca.oap = &oa;

 if (half) {
   // Scroll [count], 'scroll' or current window height lines.
   if (count) {
     curwin->w_p_scr = MIN(curwin->w_view_height, count);
   }
   count = MIN(curwin->w_view_height, (int)curwin->w_p_scr);

   int curscount = count;
   // Adjust count so as to not reveal end of buffer lines.
   if (dir == FORWARD
       && (curwin->w_topline + curwin->w_view_height + count > buflen
           || win_lines_concealed(curwin))) {
     int n = plines_correct_topline(curwin, curwin->w_topline, NULL, false, NULL);
     if (n - count < curwin->w_view_height && curwin->w_topline < buflen) {
       n += plines_m_win(curwin, curwin->w_topline + 1, buflen, curwin->w_view_height + count);
     }
     if (n < curwin->w_view_height + count) {
       count = n - curwin->w_view_height;
     }
   }

   // (Try to) scroll the window unless already at the end of the buffer.
   if (count > 0) {
     did_move = scroll_with_sms(dir, count, &curscount);
     curwin->w_cursor.lnum = prev_lnum;
     curwin->w_cursor.col = prev_col;
     curwin->w_curswant = prev_curswant;
   }

   // Move the cursor the same amount of screen lines, skipping over
   // concealed lines as those were not included in "curscount".
   if (curwin->w_p_wrap) {
     nv_screengo(&oa, dir, curscount, true);
   } else if (dir == FORWARD) {
     cursor_down_inner(curwin, curscount, true);
   } else {
     cursor_up_inner(curwin, curscount, true);
   }
 } else {
   // Scroll [count] times 'window' or current window height lines.
   count *= ((ONE_WINDOW && p_window > 0 && p_window < Rows - 1)
             ? MAX(1, (int)p_window - 2) : get_scroll_overlap(dir));
   did_move = scroll_with_sms(dir, count, &count);

   if (did_move) {
     // Place cursor at top or bottom of window.
     validate_botline_win(curwin);
     linenr_T lnum = (dir == FORWARD ? curwin->w_topline : curwin->w_botline - 1);
     // In silent Ex mode the value of w_botline - 1 may be 0,
     // but cursor lnum needs to be at least 1.
     curwin->w_cursor.lnum = MAX(lnum, 1);
   }
 }

 if (get_scrolloff_value(curwin) > 0) {
   cursor_correct(curwin);
 }
 // Move cursor to first line of closed fold.
 foldAdjustCursor(curwin);

 did_move = did_move
            || prev_col != curwin->w_cursor.col
            || prev_lnum != curwin->w_cursor.lnum;

 // Error if both the viewport and cursor did not change.
 if (!did_move) {
   beep_flush();
 } else if (!curwin->w_p_sms) {
   beginline(BL_SOL | BL_FIX);
 } else if (p_sol) {
   nv_g_home_m_cmd(&ca);
 }

 return did_move ? OK : FAIL;
}

void do_check_cursorbind(void)
{
 static win_T *prev_curwin = NULL;
 static pos_T prev_cursor = { 0, 0, 0 };

 if (curwin == prev_curwin && equalpos(curwin->w_cursor, prev_cursor)) {
   return;
 }
 prev_curwin = curwin;
 prev_cursor = curwin->w_cursor;

 linenr_T line = curwin->w_cursor.lnum;
 colnr_T col = curwin->w_cursor.col;
 colnr_T coladd = curwin->w_cursor.coladd;
 colnr_T curswant = curwin->w_curswant;
 bool set_curswant = curwin->w_set_curswant;
 win_T *old_curwin = curwin;
 buf_T *old_curbuf = curbuf;
 int old_VIsual_select = VIsual_select;
 int old_VIsual_active = VIsual_active;

 // loop through the cursorbound windows
 VIsual_select = VIsual_active = false;
 FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
   curwin = wp;
   curbuf = curwin->w_buffer;
   // skip original window and windows with 'nocursorbind'
   if (curwin != old_curwin && curwin->w_p_crb) {
     if (curwin->w_p_diff) {
       curwin->w_cursor.lnum =
         diff_get_corresponding_line(old_curbuf, line);
     } else {
       curwin->w_cursor.lnum = line;
     }
     curwin->w_cursor.col = col;
     curwin->w_cursor.coladd = coladd;
     curwin->w_curswant = curswant;
     curwin->w_set_curswant = set_curswant;

     // Make sure the cursor is in a valid position.  Temporarily set
     // "restart_edit" to allow the cursor to be beyond the EOL.
     {
       int restart_edit_save = restart_edit;
       restart_edit = true;
       check_cursor(curwin);

       // Avoid a scroll here for the cursor position, 'scrollbind' is
       // more important.
       if (!curwin->w_p_scb) {
         validate_cursor(curwin);
       }

       restart_edit = restart_edit_save;
     }
     // Correct cursor for multi-byte character.
     mb_adjust_cursor();
     redraw_later(curwin, UPD_VALID);

     // Only scroll when 'scrollbind' hasn't done this.
     if (!curwin->w_p_scb) {
       update_topline(curwin);
     }
     curwin->w_redr_status = true;
   }
 }

 // reset current-window
 VIsual_select = old_VIsual_select;
 VIsual_active = old_VIsual_active;
 curwin = old_curwin;
 curbuf = old_curbuf;
}