Fix hscroll of R2L lines that begin with a TAB or another wide glyph.

 src/xdisp.c (append_stretch_glyph): In a R2L glyph row, decrease the
 pixel width of the first glyph that is hscrolled from display.
 (display_line): In R2L glyph rows, don't give a negative offset to
 row->x when the first glyph begins before first_visible_x.

2 files changed, 38 insertions, 3 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index a86b695e147..9d5e7687110 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2014-07-29  Eli Zaretskii  <eliz@gnu.org>
+
+        Fix hscroll of R2L lines that begin with a TAB or another wide glyph.
+        * xdisp.c (append_stretch_glyph): In a R2L glyph row, decrease the
+        pixel width of the first glyph that is hscrolled from display.
+        (display_line): In R2L glyph rows, don't give a negative offset to
+        row->x when the first glyph begins before first_visible_x.
+
 2014-07-29  Andreas Schwab  <schwab@suse.de>
 
         * macros.c (Fstart_kbd_macro): Initialize kbd_macro_ptr and
diff --git a/src/xdisp.c b/src/xdisp.c
index 5cd90136ee6..e9e8ad6594e 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -20188,7 +20188,12 @@ display_line (struct it *it)
                                   it->max_phys_ascent + it->max_phys_descent);
           row->extra_line_spacing = max (row->extra_line_spacing,
                                          it->max_extra_line_spacing);
-          if (it->current_x - it->pixel_width < it->first_visible_x)
+          if (it->current_x - it->pixel_width < it->first_visible_x
+              /* In R2L rows, we arrange in extend_face_to_end_of_line
+                 to add a right offset to the line, by a suitable
+                 change to the stretch glyph that is the leftmost
+                 glyph of the line.  */
+              && !row->reversed_p)
             row->x = x - it->first_visible_x;
           /* Record the maximum and minimum buffer positions seen so
              far in glyphs that will be displayed by this row.  */
@@ -20402,9 +20407,13 @@ display_line (struct it *it)
                   if (it->bidi_p)
                     RECORD_MAX_MIN_POS (it);
 
-                  if (x < it->first_visible_x)
+                  if (x < it->first_visible_x && !row->reversed_p)
                     /* Glyph is partially visible, i.e. row starts at
-                       negative X position.  */
+                       negative X position.  Don't do that in R2L
+                       rows, where we arrange to add a right offset to
+                       the line in extend_face_to_end_of_line, by a
+                       suitable change to the stretch glyph that is
+                       the leftmost glyph of the line.  */
                     row->x = x - it->first_visible_x;
                 }
               else
@@ -25295,6 +25304,24 @@ append_stretch_glyph (struct it *it, Lisp_Object object,
           for (g = glyph - 1; g >= it->glyph_row->glyphs[area]; g--)
             g[1] = *g;
           glyph = it->glyph_row->glyphs[area];
+
+          /* Decrease the width of the first glyph of the row that
+             begins before first_visible_x (e.g., due to hscroll).
+             This is so the overall width of the row becomes smaller
+             by the scroll amount, and the stretch glyph appended by
+             extend_face_to_end_of_line will be wider, to shift the
+             row glyphs to the right.  (In L2R rows, the corresponding
+             left-shift effect is accomplished by setting row->x to a
+             negative value, which won't work with R2L rows.)
+
+             This must leave us with a positive value of WIDTH, since
+             otherwise the call to move_it_in_display_line_to at the
+             beginning of display_line would have got past the entire
+             first glyph, and then it->current_x would have been
+             greater or equal to it->first_visible_x.  */
+          if (it->current_x < it->first_visible_x)
+            width -= it->first_visible_x - it->current_x;
+          eassert (width > 0);
         }
       glyph->charpos = CHARPOS (it->position);
       glyph->object = object;