Re: Changes in frame/window code

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 18 Aug 2014 19:22:46 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: emacs-devel@gnu.org
> 
> > Date: Mon, 18 Aug 2014 18:11:19 +0200
> > From: martin rudalics <rudalics@gmx.at>
> > CC: emacs-devel@gnu.org
> > 
> >  > but it's still unclear to me why this problem is not visible
> >  > in L2R buffers.
> > 
> > Because for L2R I count the part from the leftmost position to the start
> > of the scroll bar thumb which is unaffected by the size of the thumb?

No, that wasn't it, see below.

> >  >    . The erratic behavior seems to be due to our own code resetting the
> >  >      thumb position right after I drag the thumb to some new position.
> >  >      The code which causes this seems to be -- surprise, surprise --
> >  >      set_horizontal_scroll_bar that calls
> >  >      set_horizontal_scroll_bar_hook passing it the previous position.
> >  >      I didn't yet figure out why this affects only R2L lines.
> > 
> > You mean that w->hscroll has its previous value in
> > 
> >        start = w->hscroll * FRAME_COLUMN_WIDTH (WINDOW_XFRAME (w));
> > 
> > in xdisp.c although w->hscroll was in between changed by
> > `scroll-bar-horizontal-drag-1'?
> 
> I didn't analyze this further, but it should be easy to verify.

I found the reason for this: w32_horizontal_scroll_bar_handle_click
reported bogus (always -1) values in the Y part of '(X . Y)' member of
the click event, when I drag the thumb.  That value is not used in L2R
paragraphs, so L2R buffers were not affected.

This is now fixed in trunk r117715.

Btw, I don't understand why in w32_horizontal_scroll_bar_handle_click
you overwrite the value reported from GetScrollInfo by
HIWORD(msg->msg.wParam).  My reading of MSDN documentation is that
they recommend to do it the other way around, since GetScrollInfo is
not limited to 16-bit values.  If using the values reported by
GetScrollInfo doesn't work well, perhaps that's because for
SB_THUMBTRACK message you need to use SIF_TRACKPOS and si.nTrackPos
rather than SIF_POS and si.nPos.