[pango] Fix justify_clusters()

[Behdad Esfahbod <behdad src gnome org>]

commit 79c7874ad58d32c2b265c725d5e7e81504046595
Author: Behdad Esfahbod <behdad behdad org>
Date:   Fri Aug 21 14:36:20 2015 +0100

    Fix justify_clusters()
    
    Was totally b0rked.  Much better now.  Should be good enough...

 pango/pango-layout.c |   82 +++++++++++++++++++++++++++----------------------
 1 files changed, 45 insertions(+), 37 deletions(-)
---
diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index 3874b2e..3f3f98f 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -5195,10 +5195,11 @@ justify_clusters (PangoLayoutLine *line,
        {
          PangoLayoutRun *run = run_iter->data;
          PangoGlyphString *glyphs = run->glyphs;
-         gboolean is_first_gap = TRUE;
          PangoGlyphItemIter cluster_iter;
          gboolean have_cluster;
          int offset;
+         gboolean first_run = run_iter == line->runs;
+         gboolean last_run = run_iter->next == NULL;
 
          /* We need character offset of the start of the run.  We don't have this.
           * Compute by counting from the beginning of the line.  The naming is
@@ -5219,58 +5220,65 @@ justify_clusters (PangoLayoutLine *line,
            {
              int i;
              int dir;
+             int width = 0;
 
              /* don't expand in the middle of graphemes */
              if (!log_attrs[offset + cluster_iter.start_char].is_cursor_position)
                continue;
 
              dir = (cluster_iter.start_glyph < cluster_iter.end_glyph) ? 1 : -1;
-             for (i = cluster_iter.start_glyph; i != cluster_iter.end_glyph; i += dir)
-               {
-                 /* also don't expand zero-width spaces at the end of runs */
-                 if (glyphs->glyphs[i].geometry.width == 0)
-                   {
-                     if (i == glyphs->num_glyphs -1)
-                       continue;
-
-                     if (i == 0 && glyphs->num_glyphs > 1 && glyphs->glyphs[i+1].attr.is_cluster_start)
-                       continue;
-                   }
-
-                 if (is_first_gap)
-                   {
-                     is_first_gap = FALSE;
-                     continue;
-                   }
-
-                 gaps_so_far++;
 
-                 if (mode == ADJUST)
-                   {
-                     int adjustment, space_left, space_right;
+             for (i = cluster_iter.start_glyph; i != cluster_iter.end_glyph; i += dir)
+               width += glyphs->glyphs[i].geometry.width;
 
-                     adjustment = (gaps_so_far * total_remaining_width) / total_gaps - added_so_far;
-                     if (is_hinted)
-                       adjustment = PANGO_UNITS_ROUND (adjustment);
-                     /* distribute to before/after */
-                     distribute_letter_spacing (adjustment, &space_left, &space_right);
+             /* also don't expand zero-width clusters. */
+             if (width == 0)
+               continue;
 
-                     if (i)
-                     {
-                       glyphs->glyphs[i-1].geometry.width    += space_left ;
-                       glyphs->glyphs[i  ].geometry.width    += space_right;
-                       glyphs->glyphs[i  ].geometry.x_offset += space_right;
+             gaps_so_far++;
 
-                       added_so_far += adjustment;
-                     }
-                   }
+             if (mode == ADJUST)
+               {
+                 int leftmost, rightmost;
+                 int adjustment, space_left, space_right;
+
+                 adjustment = ((gaps_so_far * total_remaining_width) - total_gaps/2) / total_gaps - 
added_so_far;
+                 if (is_hinted)
+                   adjustment = PANGO_UNITS_ROUND (adjustment);
+                 /* distribute to before/after */
+                 distribute_letter_spacing (adjustment, &space_left, &space_right);
+
+                 if (cluster_iter.start_glyph < cluster_iter.end_glyph)
+                 {
+                   /* LTR */
+                   leftmost  = cluster_iter.start_glyph;
+                   rightmost = cluster_iter.end_glyph - 1;
+                 }
+                 else
+                 {
+                   /* RTL */
+                   leftmost  = cluster_iter.end_glyph + 1;
+                   rightmost = cluster_iter.start_glyph;
+                 }
+                 /* Don't add to left-side of left-most glyph of left-most run. */
+                 if (!first_run || leftmost)
+                 {
+                   added_so_far += adjustment;
+                   glyphs->glyphs[leftmost ].geometry.width    += space_left ;
+                   glyphs->glyphs[leftmost ].geometry.x_offset += space_left ;
+                 }
+                 /* Don't add to right-side of right-most glyph of right-most run. */
+                 if (!last_run || rightmost != glyphs->num_glyphs - 1)
+                 {
+                   glyphs->glyphs[rightmost].geometry.width  += space_right;
+                 }
                }
            }
        }
 
       if (mode == MEASURE)
        {
-         total_gaps = gaps_so_far;
+         total_gaps = gaps_so_far - 1;
 
          if (total_gaps == 0)
            {