Subject: Re: bug#14567: Scrolling of large images

From: Thomas Wiecki <[email-masked]>
Date: Sat, 8 Jun 2013 11:52:39 -0400

Thanks! Which branch is this based off of? I tried it on bzr trunk (bzr://
bzr.savannah.gnu.org/emacs/trunk) but got:
patching file lisp/simple.el
Hunk #1 FAILED at 4738.
Hunk #2 FAILED at 4761.
Hunk #3 FAILED at 4808.
3 out of 3 hunks FAILED -- saving rejects to file lisp/simple.el.rej
patching file src/xdisp.

On Sat, Jun 8, 2013 at 10:19 AM, Eli Zaretskii <[email-masked]> wrote:

> > Date: Thu, 06 Jun 2013 20:32:15 +0300
> > From: Eli Zaretskii <[email-masked]>
> > Cc: [email-masked]
> >
> > > From: Thomas Wiecki <[email-masked]>
> > > Date: Thu, 6 Jun 2013 13:16:43 -0400
> > > Cc: [email-masked]
> > >
> > > 1. Download a large image (e.g.
> > >
> http://cdn.urbanislandz.com/wp-content/uploads/2011/10/MMSposter-large.jpg
> )
> > > and save it as /tmp/test.jpg
> > > 2. In an emacs buffer type "(insert-image (create-image
> "/tmp/test.jpg"))"
> > > 3. Type some arbitrary lines of text below this line.
> > > 4. In first line (containing insert-image), type C-x C-e at end of
> line to
> > > load the image.
> > > 5. Image should appear in buffer.
> > > 6. Scroll down repeatedly until past the image.
> > >
> > > Expected behavior: Scrolls down smoothly even once scrolled past image.
> > > Observed behavior: Scrolls down smoothly until end of image is
> reached. At
> > > end of image, the next scroll causes a huge jump in the window so that
> and
> > > only the text is shown but not any of the residual image.
> > >
> > > 7. scroll back up
> > >
> > > Expected behavior: Scrolls upwards over image.
> > > Observed behavior: Jumps over complete image and shows beginning of
> buffer.
> >
> > Perfect, thanks.  I will take a look.
>
> Can you try the changes below and see if they give good results,
> including in the real-life use cases where you bumped into this?  Note
> that you will have to rebuild Emacs to try this.
>
> Thanks.
>
> === modified file 'lisp/simple.el'
> --- lisp/simple.el      2013-06-05 18:10:27 +0000
> +++ lisp/simple.el      2013-06-08 14:14:39 +0000
> @@ -4738,20 +4738,35 @@ 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))))
>         (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)
> +                  (<= this-height fch))
> +              (or (null rbot) (= rbot 0)))
>           nil)
> -        ;; If cursor is not in the bottom scroll margin, move forward.
> -        ((and (> vpos 0)
> +        ;; If cursor is not in the bottom scroll margin, and the
> +        ;; current line is is not too tall, move forward.
> +        ((and (<= this-height fch)
> +              (> vpos 0)
>                (< (setq py
>                         (or (nth 1 (window-line-height))
>                             (let ((ppos (posn-at-point)))
> @@ -4761,9 +4776,10 @@ lines."
>           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 (> rbot 0)
> +                   (> 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)
> @@ -4808,7 +4824,14 @@ 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.
>
> === modified file 'src/xdisp.c'
> --- src/xdisp.c 2013-06-06 16:35:31 +0000
> +++ src/xdisp.c 2013-06-08 14:02:28 +0000
> @@ -1217,6 +1217,24 @@ line_bottom_y (struct it *it)
>    return line_top_y + line_height;
>  }
>
> +DEFUN ("line-pixel-height", Fline_pixel_height,
> +       Sline_pixel_height, 0, 0, 0,
> +       doc: /* Return height in pixels of text line in the selected
> window.
> +
> +Value is the height in pixels of the line at point.  */)
> +  (void)
> +{
> +  struct it it;
> +  struct text_pos pt;
> +  struct window *w = XWINDOW (selected_window);
> +
> +  SET_TEXT_POS (pt, PT, PT_BYTE);
> +  start_display (&it, w, pt);
> +  it.vpos = it.current_y = 0;
> +  last_height = 0;
> +  return make_number (line_bottom_y (&it));
> +}
> +
>  /* Subroutine of pos_visible_p below.  Extracts a display string, if
>     any, from the display spec given as its argument.  */
>  static Lisp_Object
> @@ -28665,6 +28683,7 @@ syms_of_xdisp (void)
>    defsubr (&Stool_bar_lines_needed);
>    defsubr (&Slookup_image_map);
>  #endif
> +  defsubr (&Sline_pixel_height);
>    defsubr (&Sformat_mode_line);
>    defsubr (&Sinvisible_p);
>    defsubr (&Scurrent_bidi_paragraph_direction);
>
>