move.c: dont invalidate viewport when no scroll happened

2 files changed, 18 insertions, 6 deletions

diff --git a/src/nvim/move.c b/src/nvim/move.c
index e2a304efa5..8084461d3a 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -1020,7 +1020,7 @@ void textpos2screenpos(win_T *wp, pos_T *pos, int *rowp, int *scolp,
 /*
  * Scroll the current window down by "line_count" logical lines.  "CTRL-Y"
  */
-void 
+bool 
 scrolldown (
     long line_count,
     int byfold              /* true: count a closed fold as one line */
@@ -1095,17 +1095,21 @@ scrolldown (
     foldAdjustCursor();
     coladvance(curwin->w_curswant);
   }
+  return moved;
 }
 
 /*
  * Scroll the current window up by "line_count" logical lines.  "CTRL-E"
  */
-void 
+bool 
 scrollup (
     long line_count,
     int byfold              /* true: count a closed fold as one line */
 )
 {
+  linenr_T topline = curwin->w_topline;
+  linenr_T botline = curwin->w_botline;
+
   if ((byfold && hasAnyFolding(curwin))
       || curwin->w_p_diff) {
     // count each sequence of folded lines as one logical line
@@ -1148,6 +1152,12 @@ scrollup (
       ~(VALID_WROW|VALID_WCOL|VALID_CHEIGHT|VALID_CROW|VALID_VIRTCOL);
     coladvance(curwin->w_curswant);
   }
+
+  bool moved = 
+    topline != curwin->w_topline ||
+    botline != curwin->w_botline;
+
+  return moved;
 }
 
 /*
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 2e49108028..f6add44f6a 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -4117,10 +4117,10 @@ void scroll_redraw(int up, long count)
   int prev_topfill = curwin->w_topfill;
   linenr_T prev_lnum = curwin->w_cursor.lnum;
 
-  if (up)
-    scrollup(count, true);
-  else
+  bool moved = up ?
+    scrollup(count, true) :
     scrolldown(count, true);
+
   if (get_scrolloff_value()) {
     // Adjust the cursor position for 'scrolloff'.  Mark w_topline as
     // valid, otherwise the screen jumps back at the end of the file.
@@ -4152,7 +4152,9 @@ void scroll_redraw(int up, long count)
   }
   if (curwin->w_cursor.lnum != prev_lnum)
     coladvance(curwin->w_curswant);
-  curwin->w_viewport_invalid = true;
+  // XXX: can `moved` be used to prevent other work here?
+  if (moved)
+    curwin->w_viewport_invalid = true;
   redraw_later(VALID);
 }