Fix bug #14567 with jumpy scrolling of tall images.

[bpt/emacs.git] / lisp / simple.el

diff --git a/lisp/simple.el b/lisp/simple.el
index 3fd94e9..34ebc8f 100644 (file)
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -4738,42 +4738,62 @@ lines."
           (vpos (nth 1 lh))
           (ypos (nth 2 lh))
           (rbot (nth 3 lh))
+          (this-lh (window-line-height))
+          (this-height (nth 0 this-lh))
+          (this-ypos (nth 2 this-lh))
+          (fch (frame-char-height))
           py vs)
       (when (or (null lh)
-               (>= rbot (frame-char-height))
-               (<= ypos (- (frame-char-height))))
+               (>= rbot fch)
+               (<= ypos (- fch))
+               (null this-lh)
+               (<= this-ypos (- fch)))
        (unless lh
          (let ((wend (pos-visible-in-window-p t nil t)))
            (setq rbot (nth 3 wend)
                  vpos (nth 5 wend))))
+       (unless this-lh
+         (let ((wstart (pos-visible-in-window-p nil nil t)))
+           (setq this-ypos (nth 2 wstart)
+                 this-height (nth 4 wstart))))
+       (setq py
+             (or (nth 1 this-lh)
+                 (let ((ppos (posn-at-point)))
+                   (cdr (or (posn-actual-col-row ppos)
+                            (posn-col-row ppos))))))
        (cond
-        ;; If last line of window is fully visible, move forward.
-        ((or (null rbot) (= rbot 0))
+        ;; If last line of window is fully visible, and vscrolling
+        ;; more would make this line invisible, move forward.
+        ((and (or (< (setq vs (window-vscroll nil t)) fch)
+                  (null this-height)
+                  (<= this-height fch))
+              (or (null rbot) (= rbot 0)))
          nil)
-        ;; If cursor is not in the bottom scroll margin, move forward.
-        ((and (> vpos 0)
-              (< (setq py
-                       (or (nth 1 (window-line-height))
-                           (let ((ppos (posn-at-point)))
-                             (cdr (or (posn-actual-col-row ppos)
-                                      (posn-col-row ppos))))))
+        ;; If cursor is not in the bottom scroll margin, and the
+        ;; current line is is not too tall, move forward.
+        ((and (or (null this-height) (<= this-height fch))
+              vpos
+              (> vpos 0)
+              (< py
                  (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)))
+        ((> vs 0)
+         (when (or (and rbot (> rbot 0))
+                   (and this-height (> this-height fch)))
+           (set-window-vscroll nil (+ vs fch) t)))
         ;; If cursor just entered the bottom scroll margin, move forward,
         ;; but also vscroll one line so redisplay won't recenter.
-        ((and (> vpos 0)
+        ((and vpos
+              (> vpos 0)
               (= 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)
+        ((and vpos (> vpos 0))
          (scroll-up 1)
          t)
         ;; Finally, start vscroll.
@@ -4808,7 +4828,14 @@ lines."
               ;; display-based motion doesn't make sense (because each
               ;; logical line occupies exactly one screen line).
               (not (> (window-hscroll) 0)))
-         (line-move-visual arg noerror)
+         (prog1 (line-move-visual arg noerror)
+           ;; If we moved into a tall line, set vscroll to make
+           ;; scrolling through tall images more smooth.
+           (let ((lh (line-pixel-height)))
+             (if (and (< arg 0)
+                      (< (point) (window-start))
+                      (> lh (frame-char-height)))
+                 (set-window-vscroll nil (- lh (frame-char-height)) t))))
        (line-move-1 arg noerror to-end)))))
 
 ;; Display-based alternative to line-move-1.