master 2e4740f: Fix pixel scrolling upwards in Info buffers

[Po Lu]

branch: master
commit 2e4740f04239ee441685b2f43d156efcf6359383
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Fix pixel scrolling upwards in Info buffers
    
    * lisp/pixel-scroll.el (pixel-point-and-height-at-unseen-line):
    Don't blindly trust window start to be the beginning of a
    visual line.
---
 lisp/pixel-scroll.el | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lisp/pixel-scroll.el b/lisp/pixel-scroll.el
index 813fbb0..432a5dc 100644
--- a/lisp/pixel-scroll.el
+++ b/lisp/pixel-scroll.el
@@ -397,7 +397,10 @@ returns nil."
 The returned value is a cons of the position of the first
 character on the unseen line just above the scope of current
 window, and the pixel height of that line."
-  (let* ((pos0 (window-start))
+  (let* ((pos0 (save-excursion
+                 (goto-char (window-start))
+                 (beginning-of-visual-line)
+                 (point)))
          (vscroll0 (window-vscroll nil t))
          (line-height nil)
          (pos
@@ -407,8 +410,7 @@ window, and the pixel height of that line."
                 (point-min)
               (vertical-motion -1)
               (setq line-height
-                    (cdr (window-text-pixel-size nil (point)
-                                                 pos0)))
+                    (cdr (window-text-pixel-size nil (point) pos0)))
               (point)))))
     ;; restore initial position
     (set-window-start nil pos0 t)