2 files changed, 18 insertions, 18 deletions

diff --git a/src/window.c b/src/window.c
index 20084a15c16..31e9782b4a8 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4970,25 +4970,21 @@ window_wants_header_line (struct window *w)
           : 0);
 }
 
-/* Return number of lines of text (not counting mode lines) in W.  */
+/* Return number of lines of text in window W, not counting the mode
+   line and header line, if any.  Do NOT use this for windows on GUI
+   frames; use window_body_height instead.  This function is only for
+   windows on TTY frames, where it is much more efficient.  */
 
 int
 window_internal_height (struct window *w)
 {
   int ht = w->total_lines;
 
-  if (!MINI_WINDOW_P (w))
-    {
-      if (!NILP (w->parent)
-          || WINDOWP (w->contents)
-          || !NILP (w->next)
-          || !NILP (w->prev)
-          || window_wants_mode_line (w))
-        --ht;
+  if (window_wants_mode_line (w))
+    --ht;
 
-      if (window_wants_header_line (w))
-        --ht;
-    }
+  if (window_wants_header_line (w))
+    --ht;
 
   return ht;
 }
@@ -5017,8 +5013,8 @@ window_scroll (Lisp_Object window, EMACS_INT n, bool whole, bool noerror)
   if (whole && Vfast_but_imprecise_scrolling)
     specbind (Qfontification_functions, Qnil);
 
-  /* If we must, use the pixel-based version which is much slower than
-     the line-based one but can handle varying line heights.  */
+  /* On GUI frames, use the pixel-based version which is much slower
+     than the line-based one but can handle varying line heights.  */
   if (FRAME_WINDOW_P (XFRAME (XWINDOW (window)->frame)))
     window_scroll_pixel_based (window, n, whole, noerror);
   else
diff --git a/src/window.h b/src/window.h
index cc0b6b6667d..b3673a0b454 100644
--- a/src/window.h
+++ b/src/window.h
@@ -93,12 +93,14 @@ struct window
     /* The frame this window is on.  */
     Lisp_Object frame;
 
-    /* Following (to right or down) and preceding (to left or up) child
-       at same level of tree.  */
+    /* Following (to right or down) and preceding (to left or up)
+       child at same level of tree.  Whether this is left/right or
+       up/down is determined by the 'horizontal' flag, see below.
+       A minibuffer window has the frame's root window pointed by 'prev'.  */
     Lisp_Object next;
     Lisp_Object prev;
 
-    /* The window this one is a child of.  */
+    /* The window this one is a child of.  For a minibuffer window: nil.  */
     Lisp_Object parent;
 
     /* The normal size of the window.  These are fractions, but we do
@@ -113,7 +115,9 @@ struct window
     Lisp_Object new_normal;
     Lisp_Object new_pixel;
 
-    /* May be buffer, window, or nil.  */
+    /* For a leaf window: a buffer; for an internal window: a window;
+       for a pseudo-window (such as menu bar or tool bar): nil.  It is
+       a buffer for a minibuffer window as well.  */
     Lisp_Object contents;
 
     /* A marker pointing to where in the text to start displaying.