vim-patch:9.1.0211: page-wise scrolling does not support smooth-scrolling

Problem:  Page-wise scrolling with Ctrl-F/Ctrl-B implements
          it's own logic to change the topline and cursor.
          In doing so, skipcol is not handled properly for
          'smoothscroll', and virtual lines.
Solution: Re-use the logic from Ctrl-E/Ctrl-Y while staying
          backward compatible as much as possible.

https://github.com/vim/vim/commit/b9f5b95b7bec2414a5a96010514702d99afea18e

2 files changed, 29 insertions, 265 deletions

diff --git a/src/nvim/move.c b/src/nvim/move.c
index 3c4da7f8ac..ebb27337f7 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -36,6 +36,7 @@
 #include "nvim/message.h"
 #include "nvim/mouse.h"
 #include "nvim/move.h"
+#include "nvim/normal.h"
 #include "nvim/option.h"
 #include "nvim/option_vars.h"
 #include "nvim/plines.h"
@@ -1552,21 +1553,6 @@ void check_topfill(win_T *wp, bool down)
   win_check_anchored_floats(wp);
 }
 
-// Use as many filler lines as possible for w_topline.  Make sure w_topline
-// is still visible.
-static void max_topfill(void)
-{
-  int n = plines_win_nofill(curwin, curwin->w_topline, true);
-  if (n >= curwin->w_height_inner) {
-    curwin->w_topfill = 0;
-  } else {
-    curwin->w_topfill = win_get_fill(curwin, curwin->w_topline);
-    if (curwin->w_topfill + n > curwin->w_height_inner) {
-      curwin->w_topfill = curwin->w_height_inner - n;
-    }
-  }
-}
-
 // Scroll the screen one line down, but don't do it if it would move the
 // cursor off the screen.
 void scrolldown_clamp(void)
@@ -1697,28 +1683,6 @@ static void botline_forw(win_T *wp, lineoff_T *lp)
   }
 }
 
-// Switch from including filler lines below lp->lnum to including filler
-// lines above loff.lnum + 1.  This keeps pointing to the same line.
-// When there are no filler lines nothing changes.
-static void botline_topline(lineoff_T *lp)
-{
-  if (lp->fill > 0) {
-    lp->lnum++;
-    lp->fill = win_get_fill(curwin, lp->lnum) - lp->fill + 1;
-  }
-}
-
-// Switch from including filler lines above lp->lnum to including filler
-// lines below loff.lnum - 1.  This keeps pointing to the same line.
-// When there are no filler lines nothing changes.
-static void topline_botline(lineoff_T *lp)
-{
-  if (lp->fill > 0) {
-    lp->fill = win_get_fill(curwin, lp->lnum) - lp->fill + 1;
-    lp->lnum--;
-  }
-}
-
 // 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").
@@ -2320,241 +2284,41 @@ void cursor_correct(win_T *wp)
 /// @return  FAIL for failure, OK otherwise.
 int onepage(Direction dir, int count)
 {
-  int retval = OK;
-  lineoff_T loff;
-  linenr_T old_topline = curwin->w_topline;
-  int so = get_scrolloff_value(curwin);
-
-  if (curbuf->b_ml.ml_line_count == 1) {    // nothing to do
-    beep_flush();
-    return FAIL;
-  }
-
-  for (; count > 0; count--) {
-    validate_botline(curwin);
-    // It's an error to move a page up when the first line is already on
-    // the screen. It's an error to move a page down when the last line
-    // is on the screen and the topline is 'scrolloff' lines from the
-    // last line.
-    if (dir == FORWARD
-        ? ((curwin->w_topline >= curbuf->b_ml.ml_line_count - so)
-           && curwin->w_botline > curbuf->b_ml.ml_line_count)
-        : (curwin->w_topline == 1
-           && curwin->w_topfill == win_get_fill(curwin, curwin->w_topline))) {
-      beep_flush();
-      retval = FAIL;
-      break;
-    }
-
-    loff.fill = 0;
-    if (dir == FORWARD) {
-      if (ONE_WINDOW && p_window > 0 && p_window < Rows - 1) {
-        // Vi compatible scrolling
-        if (p_window <= 2) {
-          curwin->w_topline++;
-        } else {
-          curwin->w_topline += (linenr_T)p_window - 2;
-        }
-        if (curwin->w_topline > curbuf->b_ml.ml_line_count) {
-          curwin->w_topline = curbuf->b_ml.ml_line_count;
-        }
-        curwin->w_cursor.lnum = curwin->w_topline;
-      } else if (curwin->w_botline > curbuf->b_ml.ml_line_count) {
-        // at end of file
-        curwin->w_topline = curbuf->b_ml.ml_line_count;
-        curwin->w_topfill = 0;
-        curwin->w_valid &= ~(VALID_WROW|VALID_CROW);
-      } else {
-        // For the overlap, start with the line just below the window
-        // and go upwards.
-        loff.lnum = curwin->w_botline;
-        loff.fill = win_get_fill(curwin, loff.lnum)
-                    - curwin->w_filler_rows;
-        get_scroll_overlap(&loff, -1);
-        curwin->w_topline = loff.lnum;
-        curwin->w_topfill = loff.fill;
-        check_topfill(curwin, false);
-        curwin->w_cursor.lnum = curwin->w_topline;
-        curwin->w_valid &= ~(VALID_WCOL|VALID_CHEIGHT|VALID_WROW|
-                             VALID_CROW|VALID_BOTLINE|VALID_BOTLINE_AP);
-      }
-    } else {  // dir == BACKWARDS
-      if (curwin->w_topline == 1) {
-        // Include max number of filler lines
-        max_topfill();
-        continue;
-      }
-      if (ONE_WINDOW && p_window > 0 && p_window < Rows - 1) {
-        // Vi compatible scrolling (sort of)
-        if (p_window <= 2) {
-          curwin->w_topline--;
-        } else {
-          curwin->w_topline -= (linenr_T)p_window - 2;
-        }
-        if (curwin->w_topline < 1) {
-          curwin->w_topline = 1;
-        }
-        curwin->w_cursor.lnum = curwin->w_topline + (linenr_T)p_window - 1;
-        if (curwin->w_cursor.lnum > curbuf->b_ml.ml_line_count) {
-          curwin->w_cursor.lnum = curbuf->b_ml.ml_line_count;
-        }
-        continue;
-      }
+  int prev_topfill = curwin->w_topfill;
+  linenr_T prev_topline = curwin->w_topline;
+  colnr_T prev_skipcol = curwin->w_skipcol;
 
-      // Find the line at the top of the window that is going to be the
-      // line at the bottom of the window.  Make sure this results in
-      // the same line as before doing CTRL-F.
-      loff.lnum = curwin->w_topline - 1;
-      loff.fill = win_get_fill(curwin, loff.lnum + 1) - curwin->w_topfill;
-      get_scroll_overlap(&loff, 1);
+  // Scroll 'window' or current window height lines.
+  count *= ((ONE_WINDOW && p_window > 0 && p_window < Rows - 1)
+            ? (int)p_window - 2 : curwin->w_height - 1);
 
-      if (loff.lnum >= curbuf->b_ml.ml_line_count) {
-        loff.lnum = curbuf->b_ml.ml_line_count;
-        loff.fill = 0;
-      } else {
-        botline_topline(&loff);
-      }
-      curwin->w_cursor.lnum = loff.lnum;
+  if (curwin->w_p_sms) {
+    scroll_redraw(dir == FORWARD, count);
+  } else {
+    // Scroll at least one full line without 'smoothscroll'.
+    count -= plines_win_nofill(curwin, curwin->w_topline, false);
+    scroll_redraw(dir == FORWARD, 1);
 
-      // Find the line just above the new topline to get the right line
-      // at the bottom of the window.
-      int n = 0;
-      while (n <= curwin->w_height_inner && loff.lnum >= 1) {
-        topline_back(curwin, &loff);
-        if (loff.height == MAXCOL) {
-          n = MAXCOL;
-        } else {
-          n += loff.height;
-        }
-      }
-      if (loff.lnum < 1) {                      // at begin of file
-        curwin->w_topline = 1;
-        max_topfill();
-        curwin->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE);
-      } else {
-        // Go two lines forward again.
-        topline_botline(&loff);
-        botline_forw(curwin, &loff);
-        botline_forw(curwin, &loff);
-        botline_topline(&loff);
-        // We're at the wrong end of a fold now.
-        hasFolding(curwin, loff.lnum, &loff.lnum, NULL);
-
-        // Always scroll at least one line.  Avoid getting stuck on
-        // very long lines.
-        if (loff.lnum >= curwin->w_topline
-            && (loff.lnum > curwin->w_topline
-                || loff.fill >= curwin->w_topfill)) {
-          // First try using the maximum number of filler lines.  If
-          // that's not enough, backup one line.
-          loff.fill = curwin->w_topfill;
-          if (curwin->w_topfill < win_get_fill(curwin, curwin->w_topline)) {
-            max_topfill();
-          }
-          if (curwin->w_topfill == loff.fill) {
-            curwin->w_topline--;
-            curwin->w_topfill = 0;
-            curwin->w_valid &= ~(VALID_WROW|VALID_CROW);
-          }
-          comp_botline(curwin);
-          curwin->w_cursor.lnum = curwin->w_botline - 1;
-          curwin->w_valid &= ~(VALID_WCOL|VALID_CHEIGHT|VALID_WROW|VALID_CROW);
-        } else {
-          curwin->w_topline = loff.lnum;
-          curwin->w_topfill = loff.fill;
-          check_topfill(curwin, false);
-          curwin->w_valid &= ~(VALID_WROW|VALID_CROW|VALID_BOTLINE);
-        }
-      }
-    }
-  }
-  foldAdjustCursor(curwin);
-  cursor_correct(curwin);
-  check_cursor_col(curwin);
-  if (retval == OK) {
-    beginline(BL_SOL | BL_FIX);
-  }
-  curwin->w_valid &= ~(VALID_WCOL|VALID_WROW|VALID_VIRTCOL);
-
-  if (retval == OK && dir == FORWARD) {
-    // Avoid the screen jumping up and down when 'scrolloff' is non-zero.
-    // But make sure we scroll at least one line (happens with mix of long
-    // wrapping lines and non-wrapping line).
-    if (check_top_offset()) {
-      scroll_cursor_top(curwin, 1, false);
-      if (curwin->w_topline <= old_topline
-          && old_topline < curbuf->b_ml.ml_line_count) {
-        curwin->w_topline = old_topline + 1;
-        hasFolding(curwin, curwin->w_topline, &curwin->w_topline, NULL);
-      }
-    } else if (curwin->w_botline > curbuf->b_ml.ml_line_count) {
-      hasFolding(curwin, curwin->w_topline, &curwin->w_topline, NULL);
+    // Temporarily set 'smoothscroll' so that scrolling count lines
+    // does not skip over parts of the buffer with wrapped lines.
+    curwin->w_p_sms = true;
+    if (count > 0) {
+      scroll_redraw(dir == FORWARD, count);
     }
+    curwin->w_p_sms = false;
   }
 
-  redraw_later(curwin, UPD_VALID);
-  return retval;
-}
-
-// 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 void get_scroll_overlap(lineoff_T *lp, int dir)
-{
-  int min_height = curwin->w_height_inner - 2;
-
-  if (lp->fill > 0) {
-    lp->height = 1;
-  } else {
-    lp->height = plines_win_nofill(curwin, lp->lnum, true);
-  }
-  int h1 = lp->height;
-  if (h1 > min_height) {
-    return;             // no overlap
-  }
-  lineoff_T loff0 = *lp;
-  if (dir > 0) {
-    botline_forw(curwin, lp);
-  } else {
-    topline_back(curwin, lp);
-  }
-  int h2 = lp->height;
-  if (h2 == MAXCOL || h2 + h1 > min_height) {
-    *lp = loff0;        // no overlap
-    return;
-  }
+  int nochange = curwin->w_topline == prev_topline
+                 && curwin->w_topfill == prev_topfill
+                 && curwin->w_skipcol == prev_skipcol;
 
-  lineoff_T loff1 = *lp;
-  if (dir > 0) {
-    botline_forw(curwin, lp);
-  } else {
-    topline_back(curwin, lp);
-  }
-  int h3 = lp->height;
-  if (h3 == MAXCOL || h3 + h2 > min_height) {
-    *lp = loff0;        // no overlap
-    return;
+  if (nochange) {
+    beep_flush();
+  } else if (!curwin->w_p_sms || curwin->w_skipcol == prev_skipcol) {
+    beginline(BL_SOL | BL_FIX);
   }
 
-  lineoff_T loff2 = *lp;
-  if (dir > 0) {
-    botline_forw(curwin, lp);
-  } else {
-    topline_back(curwin, lp);
-  }
-  int h4 = lp->height;
-  if (h4 == MAXCOL || h4 + h3 + h2 > min_height || h3 + h2 + h1 > min_height) {
-    *lp = loff1;        // 1 line overlap
-  } else {
-    *lp = loff2;        // 2 lines overlap
-  }
+  return nochange;
 }
 
 // Scroll 'scroll' lines up or down.
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 6bfeee75e6..a7c5a97d02 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -7663,8 +7663,8 @@ return {
         highlighted with |hl-NonText|.
         You may also want to add "lastline" to the 'display' option to show as
         much of the last line as possible.
-        NOTE: only partly implemented, currently works with CTRL-E, CTRL-Y
-        and scrolling with the mouse.
+        NOTE: only partly implemented, currently works with CTRL-E, CTRL-Y,
+        CTRL-B, CTRL-F and scrolling with the mouse.
       ]=],
       full_name = 'smoothscroll',
       pv_name = 'p_sms',