(line-move-partial): Use window-line-visiblity to

quickly check whether last line is partially visible, and only do
the hard (and slow) part in that case.

1 files changed, 43 insertions, 37 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index ba80ebcb9d1..5c7cca5b31e 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -3487,43 +3487,49 @@ Outline mode sets this."
           (set-window-vscroll nil (- vs (frame-char-height)) t)))
 
     ;; Move forward (down).
-    (let* ((evis (or (pos-visible-in-window-p (window-end nil t) nil t)
-                     (pos-visible-in-window-p (1- (window-end nil t)) nil t)))
-           (rbot (nth 3 evis))
-           (vpos (nth 5 evis))
-           ppos py vs)
-      (cond
-       ;; Last window line should be visible - fail if not.
-       ((null evis)
-        nil)
-       ;; If last line of window is fully visible, move forward.
-       ((null rbot)
-        nil)
-       ;; If cursor is not in the bottom scroll margin, move forward.
-       ((< (setq ppos (posn-at-point)
-                 py (cdr (or (posn-actual-col-row ppos)
-                             (posn-col-row ppos))))
-           (min (- (window-text-height) scroll-margin 1) (1- vpos)))
-        nil)
-       ;; When already vscrolled, we vscroll some more if we can,
-       ;; or clear vscroll and move forward at end of tall image.
-       ((> (setq vs (window-vscroll nil t)) 0)
-        (when (> rbot 0)
-          (set-window-vscroll nil (+ vs (min rbot (frame-char-height))) t)))
-       ;; If cursor just entered the bottom scroll margin, move forward,
-       ;; but also vscroll one line so redisplay wont recenter.
-       ((= py (min (- (window-text-height) scroll-margin 1)
-                   (1- vpos)))
-        (set-window-vscroll nil (frame-char-height) t)
-        (line-move-1 arg noerror to-end)
-        t)
-       ;; If there are lines above the last line, scroll-up one line.
-       ((> vpos 0)
-        (scroll-up 1)
-        t)
-       ;; Finally, start vscroll.
-       (t
-        (set-window-vscroll nil (frame-char-height) t))))))
+    (let ((wvis (window-line-visibility)))
+      (when (or (null wvis)
+                (and (consp wvis)
+                     (or (>= (car wvis) (frame-char-height))
+                         (>= (cdr wvis) (frame-char-height)))))
+        (let* ((wend (window-end nil t))
+               (evis (or (pos-visible-in-window-p wend nil t)
+                         (pos-visible-in-window-p (1- wend) nil t)))
+               (rbot (nth 3 evis))
+               (vpos (nth 5 evis))
+               ppos py vs)
+          (cond
+           ;; Last window line should be visible - fail if not.
+           ((null evis)
+            nil)
+           ;; If last line of window is fully visible, move forward.
+           ((null rbot)
+            nil)
+           ;; If cursor is not in the bottom scroll margin, move forward.
+           ((< (setq ppos (posn-at-point)
+                     py (cdr (or (posn-actual-col-row ppos)
+                                 (posn-col-row ppos))))
+               (min (- (window-text-height) scroll-margin 1) (1- vpos)))
+            nil)
+           ;; When already vscrolled, we vscroll some more if we can,
+           ;; or clear vscroll and move forward at end of tall image.
+           ((> (setq vs (window-vscroll nil t)) 0)
+            (when (> rbot 0)
+              (set-window-vscroll nil (+ vs (min rbot (frame-char-height))) t)))
+           ;; If cursor just entered the bottom scroll margin, move forward,
+           ;; but also vscroll one line so redisplay wont recenter.
+           ((= py (min (- (window-text-height) scroll-margin 1)
+                       (1- vpos)))
+            (set-window-vscroll nil (frame-char-height) t)
+            (line-move-1 arg noerror to-end)
+            t)
+           ;; If there are lines above the last line, scroll-up one line.
+           ((> vpos 0)
+            (scroll-up 1)
+            t)
+           ;; Finally, start vscroll.
+           (t
+            (set-window-vscroll nil (frame-char-height) t))))))))
 
 
 ;; This is like line-move-1 except that it also performs