(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.

diff --git a/lisp/simple.el b/lisp/simple.el
index ba80ebcb9d145fcf6e06d8d05c21dbb44b62f158..5c7cca5b31e0b3da3a2b2fadba27fbb8c2e4a394 100644 (file)
--- 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