[pango] Improve justify_cluster() some more

[Behdad Esfahbod <behdad src gnome org>]

commit aa12788659f2a65314bdcc005d50105a5f4a63cd
Author: Behdad Esfahbod <behdad behdad org>
Date:   Fri Aug 21 16:27:31 2015 +0100

    Improve justify_cluster() some more
    
    Much better now.
    
    Now I see issues in justify_words() again :(.

 pango/pango-layout.c |   55 ++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 40 insertions(+), 15 deletions(-)
---
diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index a9241c1..57e8e8f 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -5188,6 +5188,11 @@ justify_clusters (PangoLayoutLine *line,
 
   for (mode = MEASURE; mode <= ADJUST; mode++)
     {
+      gboolean leftedge = TRUE;
+      PangoGlyphString *rightmost_glyphs = NULL;
+      int rightmost_space;
+      int residual = 0;
+
       added_so_far = 0;
       gaps_so_far = 0;
 
@@ -5197,9 +5202,10 @@ justify_clusters (PangoLayoutLine *line,
          PangoGlyphString *glyphs = run->glyphs;
          PangoGlyphItemIter cluster_iter;
          gboolean have_cluster;
+         int dir;
          int offset;
-         gboolean first_run = run_iter == line->runs;
-         gboolean last_run = run_iter->next == NULL;
+
+         dir = run->item->analysis.level % 2 == 0 ? +1 : -1;
 
          /* 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
@@ -5214,20 +5220,21 @@ justify_clusters (PangoLayoutLine *line,
                 + pango_utf8_strlen (text + state->line_start_index,
                                      run->item->offset - state->line_start_index);
 
-         for (have_cluster = pango_glyph_item_iter_init_start (&cluster_iter, run, text);
+         for (have_cluster = dir > 0 ?
+                pango_glyph_item_iter_init_start (&cluster_iter, run, text) :
+                pango_glyph_item_iter_init_end   (&cluster_iter, run, text);
               have_cluster;
-              have_cluster = pango_glyph_item_iter_next_cluster (&cluster_iter))
+              have_cluster = dir > 0 ?
+                pango_glyph_item_iter_next_cluster (&cluster_iter) :
+                pango_glyph_item_iter_prev_cluster (&cluster_iter))
            {
              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)
                width += glyphs->glyphs[i].geometry.width;
 
@@ -5242,9 +5249,13 @@ justify_clusters (PangoLayoutLine *line,
                  int leftmost, rightmost;
                  int adjustment, space_left, space_right;
 
-                 adjustment = ((gaps_so_far * total_remaining_width) - total_remaining_width/2) / total_gaps 
- added_so_far;
+                 adjustment = total_remaining_width / total_gaps + residual;
                  if (is_hinted)
+                 {
+                   int old_adjustment = adjustment;
                    adjustment = PANGO_UNITS_ROUND (adjustment);
+                   residual = old_adjustment - adjustment;
+                 }
                  /* distribute to before/after */
                  distribute_letter_spacing (adjustment, &space_left, &space_right);
 
@@ -5260,17 +5271,23 @@ justify_clusters (PangoLayoutLine *line,
                    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)
+                 /* Don't add to left-side of left-most glyph of left-most non-zero run. */
+                 if (leftedge)
+                   leftedge = FALSE;
+                 else
                  {
-                   added_so_far += adjustment;
-                   glyphs->glyphs[leftmost ].geometry.width    += space_left ;
-                   glyphs->glyphs[leftmost ].geometry.x_offset += space_left ;
+                   glyphs->glyphs[leftmost].geometry.width    += space_left ;
+                   glyphs->glyphs[leftmost].geometry.x_offset += space_left ;
+                   added_so_far += space_left;
                  }
-                 /* Don't add to right-side of right-most glyph of right-most run. */
-                 if (!last_run || rightmost != glyphs->num_glyphs - 1)
+                 /* Don't add to right-side of right-most glyph of right-most non-zero run. */
                  {
+                   /* Save so we can undo later. */
+                   rightmost_glyphs = glyphs;
+                   rightmost_space = space_right;
+
                    glyphs->glyphs[rightmost].geometry.width  += space_right;
+                   added_so_far += space_right;
                  }
                }
            }
@@ -5286,6 +5303,14 @@ justify_clusters (PangoLayoutLine *line,
              return;
            }
        }
+      else /* mode == ADJUST */
+        {
+         if (rightmost_glyphs)
+          {
+            rightmost_glyphs->glyphs[rightmost_glyphs->num_glyphs - 1].geometry.width -= rightmost_space;
+            added_so_far -= rightmost_space;
+          }
+       }
     }
 
   state->remaining_width -= added_so_far;