Preliminary attempt to fix horizontal scroll bar dragging with bidi text.

* w32term.c (w32_horizontal_scroll_bar_handle_click): In y part
of emacs_event return length from si.nPage to si.nMax.
* xdisp.c (set_horizontal_scroll_bar): For right-to-left text
interchange start and end of thumb.
* scroll-bar.el (scroll-bar-horizontal-drag-1): Use cdr of
portion-whole for scrolling right-to-left text.

lisp/ChangeLog

+2014-08-16  Martin Rudalics  <rudalics@gmx.at>
+
+	* scroll-bar.el (scroll-bar-horizontal-drag-1): Use cdr of
+	portion-whole for scrolling right-to-left text.
+
 2014-08-15  Leo Liu  <sdl.web@gmail.com>
 	* speedbar.el (speedbar-generic-list-tag-p): Allow special

lisp/scroll-bar.el

@@ -327,8 +327,11 @@ If you click outside the slider, the window scrolls to bring the slider there."
 	 (window (nth 0 start-position))
 	 (portion-whole (nth 2 start-position))
 	 (unit (frame-char-width (window-frame window))))
-    (set-window-hscroll
-     window (/ (1- (+ (car portion-whole) unit)) unit))))
+    (if (eq (current-bidi-paragraph-direction) 'left-to-right)
+	(set-window-hscroll
+	 window (/ (1- (+ (car portion-whole) unit)) unit))
+      (set-window-hscroll
+	 window (/ (1- (+ (cdr portion-whole) unit)) unit)))))
 
 (defun scroll-bar-horizontal-drag (event)
   "Scroll the window horizontally by dragging the scroll bar slider.

src/ChangeLog

+2014-08-16  Martin Rudalics  <rudalics@gmx.at>
+
+	* w32term.c (w32_horizontal_scroll_bar_handle_click): In y part
+	of emacs_event return length from si.nPage to si.nMax.
+	* xdisp.c (set_horizontal_scroll_bar): For right-to-left text
+	interchange start and end of thumb.
+
 2014-08-15  Ken Brown  <kbrown@cornell.edu>
 	* gmalloc.c (_malloc_mutex, _aligned_blocks_mutex) [CYGWIN]: Use

src/w32term.c

@@ -4272,15 +4272,15 @@ w32_horizontal_scroll_bar_handle_click (struct scroll_bar *bar, W32Msg *msg,
 
   {
     int left_range = HORIZONTAL_SCROLL_BAR_LEFT_RANGE (f, bar->width);
-    int x;
+    int x, y;
     int dragging = bar->dragging;
     SCROLLINFO si;
 
     si.cbSize = sizeof (si);
-    si.fMask = SIF_POS;
-
+    si.fMask = SIF_POS | SIF_PAGE | SIF_RANGE;
     GetScrollInfo ((HWND) msg->msg.lParam, SB_CTL, &si);
     x = si.nPos;
+    y = si.nMax - si.nPos - si.nPage;
 
     bar->dragging = 0;
     FRAME_DISPLAY_INFO (f)->last_mouse_scroll_bar_pos = msg->msg.wParam;
@@ -4354,7 +4354,7 @@ w32_horizontal_scroll_bar_handle_click (struct scroll_bar *bar, W32Msg *msg,
       }
 
     XSETINT (emacs_event->x, x);
-    XSETINT (emacs_event->y, left_range);
+    XSETINT (emacs_event->y, y);
 
     return TRUE;
   }

src/xdisp.c

@@ -15779,7 +15779,7 @@ set_vertical_scroll_bar (struct window *w)
 void
 set_horizontal_scroll_bar (struct window *w)
 {
-  int start, end, whole, box_width;
+  int start, end, whole, portion;
   if (!MINI_WINDOW_P (w)
       || (w == XWINDOW (minibuf_window)
@@ -15806,14 +15806,25 @@ set_horizontal_scroll_bar (struct window *w)
 			  MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y); */
       start = w->hscroll * FRAME_COLUMN_WIDTH (WINDOW_XFRAME (w));
-      box_width = window_box_width (w, TEXT_AREA);
-      end = start + box_width;
-      /* The following is needed to ensure that if after maximizing a
-	 window we get hscroll > 0, we can still drag the thumb to the
-	 left.  */
-      whole = max (whole, w->hscroll + box_width);
-      whole = max (whole, end - start);
+      end = start + window_box_width (w, TEXT_AREA);
+      portion = end - start;
+      /* After enlarging a horizontally scrolled window such that it
+	 gets at least as wide as the text it contains, make sure that
+	 the thumb doesn't fill the entire scroll bar so we can still
+	 drag it back to see the entire text.  */
+      whole = max (whole, end);
+      if (it.bidi_p)
+	{
+	  Lisp_Object pdir;
+
+	  pdir = Fcurrent_bidi_paragraph_direction (Qnil);
+	  if (EQ (pdir, Qright_to_left))
+	    {
+	      start = whole - end;
+	      end = start + portion;
+	    }
+	}
       if (old_buffer)
 	set_buffer_internal (old_buffer);
@@ -15826,7 +15837,7 @@ set_horizontal_scroll_bar (struct window *w)
   /* Indicate what this scroll bar ought to be displaying now.  */
   if (FRAME_TERMINAL (XFRAME (w->frame))->set_horizontal_scroll_bar_hook)
     (*FRAME_TERMINAL (XFRAME (w->frame))->set_horizontal_scroll_bar_hook)
-      (w, end - start, whole, start);
+      (w, portion, whole, start);
 }