Add horizontal displacement

Apply horizontal displacements for superscripts and subscripts
that are provided in font metrics. This noticably improves the
placement of superscripts in italics.

Currently, we only apply these displacements in post-processing,
and ignore the width changes during line-breaking. This could
be improved by moving the baseline handling into the line-breaking
proper.

1 files changed, 60 insertions, 34 deletions

diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index 6c1e2e5e..098e3a3e 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -6154,18 +6154,23 @@ justify_words (PangoLayoutLine *line,
 
 typedef struct {
   PangoAttribute *attr;
-  int shift;
+  int x_offset;
+  int y_offset;
 } BaselineItem;
 
 static void
-collect_shifts (ParaBreakState *state,
-                PangoItem      *item,
-                PangoItem      *prev,
-                int            *start_shift,
-                int            *end_shift)
-{
-  *start_shift = 0;
-  *end_shift = 0;
+collect_baseline_shift (ParaBreakState *state,
+                        PangoItem      *item,
+                        PangoItem      *prev,
+                        int            *start_x_offset,
+                        int            *start_y_offset,
+                        int            *end_x_offset,
+                        int            *end_y_offset)
+{
+  *start_x_offset = 0;
+  *start_y_offset = 0;
+  *end_x_offset = 0;
+  *end_y_offset = 0;
 
   for (GSList *l = item->analysis.extra_attrs; l; l = l->next)
     {
@@ -6175,8 +6180,8 @@ collect_shifts (ParaBreakState *state,
         {
           int value = ((PangoAttrInt *)attr)->value;
 
-          *start_shift += value;
-          *end_shift -= value;
+          *start_y_offset += value;
+          *end_y_offset -= value;
         }
       else if (attr->klass->type == PANGO_ATTR_BASELINE_SHIFT)
         {
@@ -6187,51 +6192,60 @@ collect_shifts (ParaBreakState *state,
 
               entry = g_new0 (BaselineItem, 1);
               entry->attr = attr;
+              state->baseline_shifts = g_list_prepend (state->baseline_shifts, entry);
 
               value = ((PangoAttrInt *)attr)->value;
 
               if (value > 1024 || value < -1024)
                 {
-                  entry->shift = value;
+                  entry->y_offset = value;
+                  /* FIXME: compute an x_offset from value to italic angle */
                 }
               else
                 {
-                  int superscript_shift = 0;
-                  int subscript_shift = 0;
-                  hb_font_t *hb_font;
+                  int superscript_x_offset = 0;
+                  int superscript_y_offset = 0;
+                  int subscript_x_offset = 0;
+                  int subscript_y_offset = 0;
 
 
                   if (prev)
                     {
-                      hb_font = pango_font_get_hb_font (prev->analysis.font);
-                      hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_SUPERSCRIPT_EM_Y_OFFSET, &superscript_shift);
-                      hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_SUBSCRIPT_EM_Y_OFFSET, &subscript_shift);
+                      hb_font_t *hb_font = pango_font_get_hb_font (prev->analysis.font);
+                      hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_SUPERSCRIPT_EM_Y_OFFSET, &superscript_y_offset);
+                      hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_SUPERSCRIPT_EM_X_OFFSET, &superscript_x_offset);
+                      hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_SUBSCRIPT_EM_Y_OFFSET, &subscript_y_offset);
+                      hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_SUBSCRIPT_EM_X_OFFSET, &subscript_x_offset);
                     }
 
-                  if (superscript_shift == 0)
-                    superscript_shift = 5000;
-                  if (subscript_shift == 0)
-                    subscript_shift = 5000;
+                  if (superscript_y_offset == 0)
+                    superscript_y_offset = 5000;
+                  if (subscript_y_offset == 0)
+                    subscript_y_offset = 5000;
 
                   switch (value)
                     {
                     case PANGO_BASELINE_SHIFT_NONE:
-                      entry->shift = 0;
+                      entry->x_offset = 0;
+                      entry->y_offset = 0;
                       break;
                     case PANGO_BASELINE_SHIFT_SUPERSCRIPT:
-                      entry->shift = superscript_shift;
+                      entry->x_offset = superscript_x_offset;
+                      entry->y_offset = superscript_y_offset;
                       break;
                     case PANGO_BASELINE_SHIFT_SUBSCRIPT:
-                      entry->shift = -subscript_shift;
+                      entry->x_offset = subscript_x_offset;
+                      entry->y_offset = -subscript_y_offset;
                       break;
                     default:
                       g_assert_not_reached ();
                     }
                 }
 
-               *start_shift += entry->shift;
-               state->baseline_shifts = g_list_prepend (state->baseline_shifts, entry);
+              *start_x_offset += entry->x_offset;
+              *start_y_offset += entry->y_offset;
             }
+
           if (attr->end_index == item->offset + item->length)
             {
               BaselineItem *entry = state->baseline_shifts->data;
@@ -6239,7 +6253,10 @@ collect_shifts (ParaBreakState *state,
               if (attr->start_index == entry->attr->start_index &&
                   attr->end_index == entry->attr->end_index &&
                   ((PangoAttrInt *)attr)->value == ((PangoAttrInt *)entry->attr)->value)
-                *end_shift -= entry->shift;
+                {
+                  *end_x_offset -= entry->x_offset;
+                  *end_y_offset -= entry->y_offset;
+                }
               else
                 g_warning ("Baseline attributes mismatch\n");
 
@@ -6251,7 +6268,7 @@ collect_shifts (ParaBreakState *state,
 }
 
 static void
-apply_baseline_shifts (PangoLayoutLine *line,
+apply_baseline_shift (PangoLayoutLine *line,
                        ParaBreakState  *state)
 {
   int y_offset = 0;
@@ -6261,13 +6278,16 @@ apply_baseline_shifts (PangoLayoutLine *line,
     {
       PangoLayoutRun *run = l->data;
       PangoItem *item = run->item;
+      int start_x_offset, end_x_offset;
       int start_y_offset, end_y_offset;
 
-      collect_shifts (state, item, prev, &start_y_offset, &end_y_offset);
+      collect_baseline_shift (state, item, prev, &start_x_offset, &start_y_offset, &end_x_offset, &end_y_offset);
 
       y_offset += start_y_offset;
 
       run->y_offset = y_offset;
+      run->start_x_offset = start_x_offset;
+      run->end_x_offset = end_x_offset;
 
       y_offset += end_y_offset;
 
@@ -6295,7 +6315,7 @@ pango_layout_line_postprocess (PangoLayoutLine *line,
    */
   line->runs = g_slist_reverse (line->runs);
 
-  apply_baseline_shifts (line, state);
+  apply_baseline_shift (line, state);
 
   /* Ellipsize the line if necessary
    */
@@ -6543,16 +6563,22 @@ update_run (PangoLayoutIter *iter,
   if (iter->run_list_link == iter->line->runs)
     iter->run_x = line_ext->logical_rect.x;
   else
-    iter->run_x += iter->run_width;
+    {
+      iter->run_x += iter->end_x_offset + iter->run_width;
+      if (iter->run)
+        iter->run_x += iter->run->start_x_offset;
+    }
 
   if (iter->run)
     {
       iter->run_width = pango_glyph_string_get_width (iter->run->glyphs);
+      iter->end_x_offset = iter->run->end_x_offset;
     }
   else
     {
       /* The empty run at the end of a line */
       iter->run_width = 0;
+      iter->end_x_offset = 0;
     }
 
   if (iter->run)
@@ -7256,7 +7282,7 @@ pango_layout_iter_get_cluster_extents (PangoLayoutIter *iter,
 
   if (ink_rect)
     {
-      ink_rect->x += iter->cluster_x;
+      ink_rect->x += iter->cluster_x + iter->run->start_x_offset;
       ink_rect->y -= iter->run->y_offset;
       offset_y (iter, &ink_rect->y);
     }
@@ -7264,7 +7290,7 @@ pango_layout_iter_get_cluster_extents (PangoLayoutIter *iter,
   if (logical_rect)
     {
       g_assert (logical_rect->width == iter->cluster_width);
-      logical_rect->x += iter->cluster_x;
+      logical_rect->x += iter->cluster_x + iter->run->start_x_offset;
       logical_rect->y -= iter->run->y_offset;
       offset_y (iter, &logical_rect->y);
     }