patch 9.0.0751: 'scrolloff' does not work well with 'smoothscroll'

Problem:    'scrolloff' does not work well with 'smoothscroll'.
Solution:   Make positioning the cursor a bit better.  Rename functions.

src/charset.c

@@ -743,13 +743,13 @@ win_chartabsize(win_T *wp, char_u *p, colnr_T col)
  * Does not handle text properties, since "s" is not a buffer line.
  */
     int
-linetabsize(char_u *s)
+linetabsize_str(char_u *s)
 {
     return linetabsize_col(0, s);
 }
 
 /*
- * Like linetabsize(), but "s" starts at column "startcol".
+ * Like linetabsize_str(), but "s" starts at column "startcol".
  */
     int
 linetabsize_col(int startcol, char_u *s)
@@ -772,7 +772,7 @@ linetabsize_col(int startcol, char_u *s)
 }
 
 /*
- * Like linetabsize(), but for a given window instead of the current one.
+ * Like linetabsize_str(), but for a given window instead of the current one.
  */
     int
 win_linetabsize(win_T *wp, linenr_T lnum, char_u *line, colnr_T len)
@@ -785,6 +785,17 @@ win_linetabsize(win_T *wp, linenr_T lnum, char_u *line, colnr_T len)
     return (int)cts.cts_vcol;
 }
 
+/*
+ * Return the number of cells line "lnum" of window "wp" will take on the
+ * screen, taking into account the size of a tab and text properties.
+ */
+  int
+linetabsize(win_T *wp, linenr_T lnum)
+{
+    return win_linetabsize(wp, lnum,
+		       ml_get_buf(wp->w_buffer, lnum, FALSE), (colnr_T)MAXCOL);
+}
+
     void
 win_linetabsize_cts(chartabsize_T *cts, colnr_T len)
 {

src/edit.c

@@ -237,7 +237,7 @@ edit(
 	if (startln)
 	    Insstart.col = 0;
     }
-    Insstart_textlen = (colnr_T)linetabsize(ml_get_curline());
+    Insstart_textlen = (colnr_T)linetabsize_str(ml_get_curline());
     Insstart_blank_vcol = MAXCOL;
     if (!did_ai)
 	ai_col = 0;
@@ -2372,7 +2372,7 @@ stop_arrow(void)
 	    // Don't update the original insert position when moved to the
 	    // right, except when nothing was inserted yet.
 	    update_Insstart_orig = FALSE;
-	Insstart_textlen = (colnr_T)linetabsize(ml_get_curline());
+	Insstart_textlen = (colnr_T)linetabsize_str(ml_get_curline());
 
 	if (u_save_cursor() == OK)
 	{

src/ex_cmds.c

@@ -256,7 +256,7 @@ linelen(int *has_tab)
 	;
     save = *last;
     *last = NUL;
-    len = linetabsize(line);		// get line length
+    len = linetabsize_str(line);	// get line length on screen
     if (has_tab != NULL)		// check for embedded TAB
 	*has_tab = (vim_strchr(first, TAB) != NULL);
     *last = save;

src/misc2.c

@@ -150,7 +150,7 @@ coladvance2(
 
 	    if ((addspaces || finetune) && !VIsual_active)
 	    {
-		curwin->w_curswant = linetabsize(line) + one_more;
+		curwin->w_curswant = linetabsize_str(line) + one_more;
 		if (curwin->w_curswant > 0)
 		    --curwin->w_curswant;
 	    }
@@ -166,7 +166,7 @@ coladvance2(
 		&& wcol >= (colnr_T)width
 		&& width > 0)
 	{
-	    csize = linetabsize(line);
+	    csize = linetabsize_str(line);
 	    if (csize > 0)
 		csize--;
 

src/move.c

@@ -1633,7 +1633,7 @@ scrolldown(
 
     if (curwin->w_cursor.lnum == curwin->w_topline && do_sms)
     {
-	long	so = curwin->w_p_so >= 0 ? curwin->w_p_so : p_so;
+	long	so = get_scrolloff_value();
 	int	scrolloff_cols = so == 0 ? 0 : width1 + (so - 1) * width2;
 
 	// make sure the cursor is in the visible text
@@ -1684,8 +1684,7 @@ scrollup(
 	linenr_T    prev_topline = curwin->w_topline;
 
 	if (do_sms)
-	    size = win_linetabsize(curwin, curwin->w_topline,
-				   ml_get(curwin->w_topline), (colnr_T)MAXCOL);
+	    size = linetabsize(curwin, curwin->w_topline);
 
 	// diff mode: first consume "topfill"
 	// 'smoothscroll': increase "w_skipcol" until it goes over the end of
@@ -1740,8 +1739,7 @@ scrollup(
 # endif
 		    curwin->w_skipcol = 0;
 		    if (todo > 1 && do_sms)
-			size = win_linetabsize(curwin, curwin->w_topline,
-				ml_get(curwin->w_topline), (colnr_T)MAXCOL);
+			size = linetabsize(curwin, curwin->w_topline);
 		}
 	    }
 	}
@@ -1784,11 +1782,15 @@ scrollup(
     {
 	int	width1 = curwin->w_width - curwin_col_off();
 	int	width2 = width1 + curwin_col_off2();
-	long	so = curwin->w_p_so >= 0 ? curwin->w_p_so : p_so;
+	long	so = get_scrolloff_value();
 	int	scrolloff_cols = so == 0 ? 0 : width1 + (so - 1) * width2;
+	int	space_cols = (curwin->w_height - 1) * width2;
 
 	// Make sure the cursor is in a visible part of the line, taking
 	// 'scrolloff' into account, but using screen lines.
+	// If there are not enough screen lines put the cursor in the middle.
+	if (scrolloff_cols > space_cols / 2)
+	    scrolloff_cols = space_cols / 2;
 	validate_virtcol();
 	if (curwin->w_virtcol < curwin->w_skipcol + 3 + scrolloff_cols)
 	{
@@ -1823,11 +1825,22 @@ adjust_skipcol(void)
 
     int	    width1 = curwin->w_width - curwin_col_off();
     int	    width2 = width1 + curwin_col_off2();
-    long    so = curwin->w_p_so >= 0 ? curwin->w_p_so : p_so;
+    long    so = get_scrolloff_value();
     int	    scrolloff_cols = so == 0 ? 0 : width1 + (so - 1) * width2;
     int	    scrolled = FALSE;
 
     validate_virtcol();
+    if (curwin->w_cline_height == curwin->w_height)
+    {
+	// the line just fits in the window, don't scroll
+	if (curwin->w_skipcol != 0)
+	{
+	    curwin->w_skipcol = 0;
+	    redraw_later(UPD_NOT_VALID);
+	}
+	return;
+    }
+
     while (curwin->w_skipcol > 0
 		 && curwin->w_virtcol < curwin->w_skipcol + 3 + scrolloff_cols)
     {
@@ -2691,6 +2704,19 @@ cursor_correct(void)
 	    )
 	return;
 
+    if (curwin->w_p_sms && !curwin->w_p_wrap)
+    {
+	// 'smoothscroll is active
+	if (curwin->w_cline_height == curwin->w_height)
+	{
+	    // The cursor line just fits in the window, don't scroll.
+	    curwin->w_skipcol = 0;
+	    return;
+	}
+	// TODO: 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:

src/normal.c

@@ -2266,7 +2266,7 @@ find_decl(
     static int
 nv_screengo(oparg_T *oap, int dir, long dist)
 {
-    int		linelen = linetabsize(ml_get_curline());
+    int		linelen = linetabsize_str(ml_get_curline());
     int		retval = OK;
     int		atend = FALSE;
     int		n;
@@ -2343,7 +2343,7 @@ nv_screengo(oparg_T *oap, int dir, long dist)
 		}
 		--curwin->w_cursor.lnum;
 
-		linelen = linetabsize(ml_get_curline());
+		linelen = linetabsize_str(ml_get_curline());
 		if (linelen > width1)
 		    curwin->w_curswant += (((linelen - width1 - 1) / width2)
 								+ 1) * width2;
@@ -2383,7 +2383,7 @@ nv_screengo(oparg_T *oap, int dir, long dist)
 		// clipped to column 0.
 		if (curwin->w_curswant >= width1)
 		    curwin->w_curswant -= width2;
-		linelen = linetabsize(ml_get_curline());
+		linelen = linetabsize_str(ml_get_curline());
 	    }
 	}
       }
@@ -6005,7 +6005,7 @@ nv_g_cmd(cmdarg_T *cap)
 	{
 	    oap->motion_type = MCHAR;
 	    oap->inclusive = FALSE;
-	    i = linetabsize(ml_get_curline());
+	    i = linetabsize_str(ml_get_curline());
 	    if (cap->count0 > 0 && cap->count0 <= 100)
 		coladvance((colnr_T)(i * cap->count0 / 100));
 	    else

src/ops.c

@@ -3261,7 +3261,7 @@ cursor_pos_info(dict_T *dict)
 		col_print(buf1, sizeof(buf1), (int)curwin->w_cursor.col + 1,
 			(int)curwin->w_virtcol + 1);
 		col_print(buf2, sizeof(buf2), (int)STRLEN(p),
-				    linetabsize(p));
+							   linetabsize_str(p));
 
 		if (char_count_cursor == byte_count_cursor
 			&& char_count == byte_count)

src/popupwin.c

@@ -1403,8 +1403,7 @@ popup_adjust_position(win_T *wp)
 	// "margin_width" is added to "len" where it matters.
 	if (wp->w_width < maxwidth)
 	    wp->w_width = maxwidth;
-	len = win_linetabsize(wp, lnum, ml_get_buf(wp->w_buffer, lnum, FALSE),
-							      (colnr_T)MAXCOL);
+	len = linetabsize(wp, lnum);
 	wp->w_width = w_width;
 
 	if (wp->w_p_wrap)

src/proto/charset.pro

@@ -15,9 +15,10 @@ int ptr2cells(char_u *p);
 int vim_strsize(char_u *s);
 int vim_strnsize(char_u *s, int len);
 int chartabsize(char_u *p, colnr_T col);
-int linetabsize(char_u *s);
+int linetabsize_str(char_u *s);
 int linetabsize_col(int startcol, char_u *s);
 int win_linetabsize(win_T *wp, linenr_T lnum, char_u *line, colnr_T len);
+int linetabsize(win_T *wp, linenr_T lnum);
 void win_linetabsize_cts(chartabsize_T *cts, colnr_T len);
 int vim_isIDc(int c);
 int vim_isNormalIDc(int c);

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    751,
 /**/
     750,
 /**/