Add a mode setting to control bar position and height.

autoload/scrollview.vim

@@ -163,7 +163,7 @@ function! s:VisibleLineCount(winid, start, end) abort
     let l:current_winid = win_getid(winnr())
     call win_gotoid(a:winid)
     let l:end = a:end
-    if l:end ==# '$'
+    if type(l:end) ==# v:t_string && l:end ==# '$'
       let l:end = line('$')
     endif
     let l:module = luaeval('require("scrollview")')
@@ -192,15 +192,35 @@ function! s:CalculatePosition(winnr) abort
   let [l:row, l:col] = win_screenpos(l:winnr)
   let l:winheight = winheight(l:winnr)
   let l:winwidth = winwidth(l:winnr)
-  " l:top is relative to the window, and 0-indexed.
+  let l:mode = s:GetVariable('scrollview_mode', l:winnr)
+  if l:mode ==# 'virtual'
+    " Update topline, botline, and line_count to correspond to virtual lines,
+    " which account for closed folds.
+    let l:virtual_counts = {
+          \   'before': s:VisibleLineCount(l:winid, 1, l:topline - 1),
+          \   'here': s:VisibleLineCount(l:winid, l:topline, l:botline),
+          \   'after': s:VisibleLineCount(l:winid, l:botline + 1, '$')
+          \ }
+    let l:topline = l:virtual_counts.before + 1
+    let l:botline = l:virtual_counts.before + l:virtual_counts.here
+    let l:line_count = l:virtual_counts.before
+          \ + l:virtual_counts.here
+          \ + l:virtual_counts.after
+  endif
+  " l:top is the position for the top of the scrollbar, relative to the
+  " window, and 0-indexed.
   let l:top = 0
   if l:line_count ># 1
     let l:top = (l:topline - 1.0) / (l:line_count - 1)
     let l:top = float2nr(round((l:winheight - 1) * l:top))
   endif
   let l:height = l:winheight
   if l:line_count ># l:height
-    let l:height = str2float(l:winheight) / l:line_count
+    let l:numerator = l:winheight
+    if l:mode ==# 'document'
+      let l:numerator = l:botline - l:topline + 1
+    endif
+    let l:height = str2float(l:numerator) / l:line_count
     let l:height = float2nr(ceil(l:height * l:winheight))
   endif
   " Make sure bar properly reflects bottom of document.
@@ -247,19 +267,22 @@ function! s:ShowScrollbar(winnr) abort
   if s:Contains(l:excluded_filetypes, l:buf_filetype)
     return
   endif
+  let l:wininfo = getwininfo(l:winid)[0]
   " Don't show in terminal mode, since the bar won't be properly updated for
   " insertions.
-  if getwininfo(l:winid)[0].terminal
+  if l:wininfo.terminal
     return
   endif
   if l:winheight ==# 0 || l:winwidth ==# 0
     return
   endif
-  let l:bar_position = s:CalculatePosition(l:winnr)
-  " Don't show the position bar when it would span the entire screen.
-  if l:winheight ==# l:bar_position.height
+  let l:line_count = nvim_buf_line_count(l:bufnr)
+  " Don't show the position bar when all lines are on screen.
+  " WARN: See the botline usage warning in CalculatePosition.
+  if l:wininfo.botline - l:wininfo.topline + 1 ==# l:line_count
     return
   endif
+  let l:bar_position = s:CalculatePosition(l:winnr)
   " Don't show scrollbar when its column is beyond what's valid.
   let l:min_valid_col = 1
   let l:max_valid_col = l:winwidth

doc/scrollview.txt

@@ -50,6 +50,9 @@ have the highest precedence, and global variables have the lowest).
 *scrollview_on_startup*                   `1`
   Specifies whether scrollbars are        Considered only at global scope
   enabled on startup
+*scrollview_mode*                         `'default'`
+  Specifies what the scrollbar            See |scrollview-modes| for details on
+  position and size correspond to         the available modes
 *scrollview_excluded_filetypes*           `[]`
   Optional file types for which
   scrollbars should not be displayed
@@ -78,6 +81,32 @@ example.
 	let g:scrollview_base = 'buffer'
 	let g:scrollview_column = 80
 
+Scrollview Modes ~
+                                           *scrollview-modes*
+The following modes are available for the |scrollview_mode| configuration
+setting (set as a |string|).
+
+Mode       Description
+----       -----------
+*default*    The scrollbar top position reflects the window's top line number
+           relative to the document's line count. The scrollbar height reflects
+           the size of the window relative to the document's line count.
+
+*document*   The scrollbar top position reflects the window's top line number
+           relative to the document's line count. The scrollbar bottom
+           position reflects the window's bottom line number relative to the
+           document's line count. Thus, the scrollbar height reflects the
+           number of lines in the window (counting lines in closed folds)
+           relative to the document's line count.
+
+*virtual*    The scrollbar position and height are calculated similarly to
+           the |default| mode, but line numbers and the document line count
+           are implicitly updated to virtual counterparts that account for
+           closed folds. The scrollbar top position reflects the window's top
+           virtual line number relative to the document's virtual line count.
+           The scrollbar height reflects the size of the window relative to
+           the document's virtual line count.
+
 Color Customization ~
                                            *scrollview-color-customization*
 The following highlight group can be configured to change |nvim-scrollview|'s

doc/tags

@@ -1,17 +1,22 @@
 :ScrollViewDisable	scrollview.txt	/*:ScrollViewDisable*
 :ScrollViewEnable	scrollview.txt	/*:ScrollViewEnable*
 :ScrollViewRefresh	scrollview.txt	/*:ScrollViewRefresh*
+default	scrollview.txt	/*default*
+document	scrollview.txt	/*document*
 nvim-scrollview	scrollview.txt	/*nvim-scrollview*
 scrollview-color-customization	scrollview.txt	/*scrollview-color-customization*
 scrollview-configuration	scrollview.txt	/*scrollview-configuration*
 scrollview-installation	scrollview.txt	/*scrollview-installation*
 scrollview-issues	scrollview.txt	/*scrollview-issues*
+scrollview-modes	scrollview.txt	/*scrollview-modes*
 scrollview-requirements	scrollview.txt	/*scrollview-requirements*
 scrollview-usage	scrollview.txt	/*scrollview-usage*
 scrollview.txt	scrollview.txt	/*scrollview.txt*
 scrollview_base	scrollview.txt	/*scrollview_base*
 scrollview_column	scrollview.txt	/*scrollview_column*
 scrollview_current_only	scrollview.txt	/*scrollview_current_only*
 scrollview_excluded_filetypes	scrollview.txt	/*scrollview_excluded_filetypes*
+scrollview_mode	scrollview.txt	/*scrollview_mode*
 scrollview_on_startup	scrollview.txt	/*scrollview_on_startup*
 scrollview_winblend	scrollview.txt	/*scrollview_winblend*
+virtual	scrollview.txt	/*virtual*

plugin/scrollview.vim

@@ -23,6 +23,7 @@ endif
 " *************************************************
 
 let g:scrollview_on_startup = get(g:, 'scrollview_on_startup', 1)
+let g:scrollview_mode = get(g:, 'scrollview_mode', 'default')
 let g:scrollview_excluded_filetypes = 
       \ get(g:, 'scrollview_excluded_filetypes', [])
 let g:scrollview_current_only = get(g:, 'scrollview_current_only', 0)