Implement baseline shifts

Add a new baseline-shift attribute, which is similar to
rise, but accumulates. In addition, it supports font-
relative values such as superscript and subscript.

We implement support for this by computing baseline
shifts for run during line post-processing, and storing
them in the runs. The renderer now takes these shifts
into account when rendering layout lines.

8 files changed, 231 insertions, 45 deletions

diff --git a/pango/pango-attributes.c b/pango/pango-attributes.c
index 326234d2..8507c963 100644
--- a/pango/pango-attributes.c
+++ b/pango/pango-attributes.c
@@ -924,6 +924,30 @@ pango_attr_rise_new (int rise)
 }
 
 /**
+ * pango_attr_baseline_shift_new:
+ * @shift: either a `PangoBaselineShift` enumeration value or an absolute value (> 1024)
+ *   in Pango units, relative to the baseline of the previous run.
+ *   Positive values displace the text upwards.
+ *
+ * Create a new baseline displacement attribute.
+ *
+ * Return value: (transfer full): the newly allocated
+ *   `PangoAttribute`, which should be freed with
+ *   [method@Pango.Attribute.destroy]
+ */
+PangoAttribute *
+pango_attr_baseline_shift_new (int rise)
+{
+  static const PangoAttrClass klass = {
+    PANGO_ATTR_BASELINE_SHIFT,
+    pango_attr_int_copy,
+    pango_attr_int_destroy,
+    pango_attr_int_equal
+  };
+
+  return pango_attr_int_new (&klass, (int)rise);
+}
+/**
  * pango_attr_scale_new:
  * @scale_factor: factor to scale the font
  *
@@ -1533,6 +1557,7 @@ pango_attribute_as_int (PangoAttribute *attr)
     case PANGO_ATTR_TEXT_TRANSFORM:
     case PANGO_ATTR_WORD:
     case PANGO_ATTR_SENTENCE:
+    case PANGO_ATTR_BASELINE_SHIFT:
       return (PangoAttrInt *)attr;
 
     default:
diff --git a/pango/pango-attributes.h b/pango/pango-attributes.h
index 613aa021..1c9df2c5 100644
--- a/pango/pango-attributes.h
+++ b/pango/pango-attributes.h
@@ -79,6 +79,7 @@ typedef struct _PangoAttrFontFeatures PangoAttrFontFeatures;
  * @PANGO_ATTR_ABSOLUTE_LINE_HEIGHT: line height ([struct@Pango.AttrInt]). Since: 1.50
  * @PANGO_ATTR_WORD: override segmentation to classify the range of the attribute as a single word ([struct@Pango.AttrInt]). Since 1.50
  * @PANGO_ATTR_SENTENCE: override segmentation to classify the range of the attribute as a single sentence ([struct@Pango.AttrInt]). Since 1.50
+ * @PANGO_ATTR_BASELINE_SHIFT: baseline displacement ([struct@Pango.AttrSize]). Since 1.50
  *
  * The `PangoAttrType` distinguishes between different types of attributes.
  *
@@ -125,6 +126,7 @@ typedef enum
   PANGO_ATTR_TEXT_TRANSFORM,    /* PangoAttrInt */
   PANGO_ATTR_WORD,              /* PangoAttrInt */
   PANGO_ATTR_SENTENCE,          /* PangoAttrInt */
+  PANGO_ATTR_BASELINE_SHIFT,    /* PangoAttrSize */
 } PangoAttrType;
 
 /**
@@ -227,6 +229,23 @@ typedef enum {
 } PangoTextTransform;
 
 /**
+ * PangoBaselineShift:
+ * @PANGO_BASELINE_SHIFT_SUPERSCRIPT: Shift the baseline to the superscript position,
+ *   relative to the previous run
+ * @PANGO_BASELINE_SHIFT_SUBSCRIPT: Shift the baseline to the subscript position,
+ *   relative to the previous run
+ *
+ * An enumeration that affects baseline shifts between runs.
+ *
+ * Since: 1.50
+ */
+typedef enum {
+  PANGO_BASELINE_SHIFT_NONE,
+  PANGO_BASELINE_SHIFT_SUPERSCRIPT,
+  PANGO_BASELINE_SHIFT_SUBSCRIPT,
+} PangoBaselineShift;
+
+/**
  * PANGO_ATTR_INDEX_FROM_TEXT_BEGINNING:
  *
  * Value for @start_index in `PangoAttribute` that indicates
@@ -515,6 +534,8 @@ PangoAttribute *        pango_attr_strikethrough_color_new      (guint16
                                                                  guint16                     blue);
 PANGO_AVAILABLE_IN_ALL
 PangoAttribute *        pango_attr_rise_new                     (int                         rise);
+PANGO_AVAILABLE_IN_1_50
+PangoAttribute *        pango_attr_baseline_shift_new           (int                         shift);
 PANGO_AVAILABLE_IN_ALL
 PangoAttribute *        pango_attr_scale_new                    (double                      scale_factor);
 PANGO_AVAILABLE_IN_1_4
diff --git a/pango/pango-glyph-item.c b/pango/pango-glyph-item.c
index 5e6ca7b6..c64bfa13 100644
--- a/pango/pango-glyph-item.c
+++ b/pango/pango-glyph-item.c
@@ -129,6 +129,8 @@ pango_glyph_item_split (PangoGlyphItem *orig,
 
   pango_glyph_string_set_size (orig->glyphs, orig->glyphs->num_glyphs - num_glyphs);
 
+  new->y_offset = orig->y_offset;
+
   return new;
 }
 
@@ -154,6 +156,7 @@ pango_glyph_item_copy  (PangoGlyphItem *orig)
 
   result->item = pango_item_copy (orig->item);
   result->glyphs = pango_glyph_string_copy (orig->glyphs);
+  result->y_offset = orig->y_offset;
 
   return result;
 }
@@ -196,7 +199,7 @@ G_DEFINE_BOXED_TYPE (PangoGlyphItem, pango_glyph_item,
  * Since: 1.22
  */
 PangoGlyphItemIter *
-pango_glyph_item_iter_copy  (PangoGlyphItemIter *orig)
+pango_glyph_item_iter_copy (PangoGlyphItemIter *orig)
 {
   PangoGlyphItemIter *result;
 
diff --git a/pango/pango-glyph-item.h b/pango/pango-glyph-item.h
index 6c2f9249..baea69fc 100644
--- a/pango/pango-glyph-item.h
+++ b/pango/pango-glyph-item.h
@@ -33,6 +33,8 @@ G_BEGIN_DECLS
  * PangoGlyphItem:
  * @item: corresponding `PangoItem`
  * @glyphs: corresponding `PangoGlyphString`
+ * @baseline: shift of the baseline, relative to the
+ *   containing lines baseline. Positive values shift upwards
  *
  * A `PangoGlyphItem` is a pair of a `PangoItem` and the glyphs
  * resulting from shaping the items text.
@@ -45,8 +47,9 @@ typedef struct _PangoGlyphItem PangoGlyphItem;
 
 struct _PangoGlyphItem
 {
-  PangoItem        *item;
+  PangoItem *item;
   PangoGlyphString *glyphs;
+  int y_offset;
 };
 
 #define PANGO_TYPE_GLYPH_ITEM (pango_glyph_item_get_type ())
diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index d3d93e60..58e3a91c 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -92,7 +92,7 @@
 typedef struct _ItemProperties ItemProperties;
 typedef struct _ParaBreakState ParaBreakState;
 
-/* Note that rise, letter_spacing, shape are constant across items,
+/* Note that letter_spacing and shape are constant across items,
  * since we pass them into itemization.
  *
  * uline and strikethrough can vary across an item, so we collect
@@ -108,7 +108,6 @@ struct _ItemProperties
   guint uline_error    : 1;
   guint strikethrough  : 1;
   guint oline_single   : 1;
-  gint            rise;
   gint            letter_spacing;
   gboolean        shape_set;
   PangoRectangle *shape_ink_rect;
@@ -3621,6 +3620,8 @@ struct _ParaBreakState
   int remaining_width;          /* Amount of space remaining on line; < 0 is infinite */
 
   int hyphen_width;             /* How much space a hyphen will take */
+
+  GList *baseline_shifts;
 };
 
 static gboolean
@@ -4324,6 +4325,7 @@ affects_itemization (PangoAttribute *attr,
     case PANGO_ATTR_LETTER_SPACING:
     case PANGO_ATTR_SHAPE:
     case PANGO_ATTR_RISE:
+    case PANGO_ATTR_BASELINE_SHIFT:
     case PANGO_ATTR_LINE_HEIGHT:
     case PANGO_ATTR_ABSOLUTE_LINE_HEIGHT:
     case PANGO_ATTR_TEXT_TRANSFORM:
@@ -4485,6 +4487,7 @@ pango_layout_check_lines (PangoLayout *layout)
 
   state.log_widths = NULL;
   state.num_log_widths = 0;
+  state.baseline_shifts = NULL;
 
   do
     {
@@ -4593,6 +4596,7 @@ pango_layout_check_lines (PangoLayout *layout)
   while (!done);
 
   g_free (state.log_widths);
+  g_list_free_full (state.baseline_shifts, g_free);
 
   apply_attributes_to_runs (layout, attrs);
   layout->lines = g_slist_reverse (layout->lines);
@@ -5220,6 +5224,7 @@ pango_layout_run_get_extents_and_height (PangoLayoutRun *run,
   PangoFontMetrics *metrics = NULL;
   gboolean has_underline;
   gboolean has_overline;
+  int y_offset;
 
   if (G_UNLIKELY (!run_ink && !run_logical && !line_logical && !height))
     return;
@@ -5313,6 +5318,8 @@ pango_layout_run_get_extents_and_height (PangoLayoutRun *run,
       *height = pango_font_metrics_get_height (metrics);
     }
 
+  y_offset = run->y_offset;
+
   if (run->item->analysis.flags & PANGO_ANALYSIS_FLAG_CENTERED_BASELINE)
     {
       gboolean is_hinted = (run_logical->y & run_logical->height & (PANGO_SCALE - 1)) == 0;
@@ -5321,17 +5328,14 @@ pango_layout_run_get_extents_and_height (PangoLayoutRun *run,
       if (is_hinted)
         adjustment = PANGO_UNITS_ROUND (adjustment);
 
-      properties.rise += adjustment;
+      y_offset += adjustment;
     }
 
-  if (properties.rise != 0)
-    {
-      if (run_ink)
-        run_ink->y -= properties.rise;
+  if (run_ink)
+    run_ink->y -= y_offset;
 
-      if (run_logical)
-        run_logical->y -= properties.rise;
-    }
+  if (run_logical)
+    run_logical->y -= y_offset;
 
   if (line_logical)
     {
@@ -6147,6 +6151,129 @@ justify_words (PangoLayoutLine *line,
   state->remaining_width -= added_so_far;
 }
 
+typedef struct {
+  PangoAttribute *attr;
+  int shift;
+} BaselineItem;
+
+static void
+collect_shifts (ParaBreakState *state,
+                PangoItem      *item,
+                PangoItem      *prev,
+                int            *start_shift,
+                int            *end_shift)
+{
+  *start_shift = 0;
+  *end_shift = 0;
+
+  for (GSList *l = item->analysis.extra_attrs; l; l = l->next)
+    {
+      PangoAttribute *attr = l->data;
+
+      if (attr->klass->type == PANGO_ATTR_RISE)
+        {
+          int value = ((PangoAttrInt *)attr)->value;
+
+          *start_shift += value;
+          *end_shift -= value;
+        }
+      else if (attr->klass->type == PANGO_ATTR_BASELINE_SHIFT)
+        {
+          if (attr->start_index == item->offset)
+            {
+              BaselineItem *entry;
+              int value;
+
+              entry = g_new0 (BaselineItem, 1);
+              entry->attr = attr;
+
+              value = ((PangoAttrInt *)attr)->value;
+
+              if (value > 1024 || value < -1024)
+                {
+                  entry->shift = value;
+                }
+              else
+                {
+                  int superscript_shift = 0;
+                  int subscript_shift = 0;
+                  hb_font_t *hb_font;
+
+
+                  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);
+                    }
+
+                  if (superscript_shift == 0)
+                    superscript_shift = 5000;
+                  if (subscript_shift == 0)
+                    subscript_shift = 5000;
+
+                  switch (value)
+                    {
+                    case PANGO_BASELINE_SHIFT_NONE:
+                      entry->shift = 0;
+                      break;
+                    case PANGO_BASELINE_SHIFT_SUPERSCRIPT:
+                      entry->shift = superscript_shift;
+                      break;
+                    case PANGO_BASELINE_SHIFT_SUBSCRIPT:
+                      entry->shift = -subscript_shift;
+                      break;
+                    default:
+                      g_assert_not_reached ();
+                    }
+                }
+
+               *start_shift += entry->shift;
+               state->baseline_shifts = g_list_prepend (state->baseline_shifts, entry);
+            }
+          if (attr->end_index == item->offset + item->length)
+            {
+              BaselineItem *entry = state->baseline_shifts->data;
+
+              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;
+              else
+                g_warning ("Baseline attributes mismatch\n");
+
+              state->baseline_shifts = g_list_remove (state->baseline_shifts, entry);
+              g_free (entry);
+            }
+        }
+    }
+}
+
+static void
+apply_baseline_shifts (PangoLayoutLine *line,
+                       ParaBreakState  *state)
+{
+  int y_offset = 0;
+  PangoItem *prev = NULL;
+
+  for (GSList *l = line->runs; l; l = l->next)
+    {
+      PangoLayoutRun *run = l->data;
+      PangoItem *item = run->item;
+      int start_y_offset, end_y_offset;
+
+      collect_shifts (state, item, prev, &start_y_offset, &end_y_offset);
+
+      y_offset += start_y_offset;
+
+      run->y_offset = y_offset;
+
+      y_offset += end_y_offset;
+
+      prev = item;
+    }
+}
+
 static void
 pango_layout_line_postprocess (PangoLayoutLine *line,
                                ParaBreakState  *state,
@@ -6167,6 +6294,8 @@ pango_layout_line_postprocess (PangoLayoutLine *line,
    */
   line->runs = g_slist_reverse (line->runs);
 
+  apply_baseline_shifts (line, state);
+
   /* Ellipsize the line if necessary
    */
   if (G_UNLIKELY (state->line_width >= 0 &&
@@ -6224,7 +6353,6 @@ pango_layout_get_item_properties (PangoItem      *item,
   properties->oline_single = FALSE;
   properties->strikethrough = FALSE;
   properties->letter_spacing = 0;
-  properties->rise = 0;
   properties->shape_set = FALSE;
   properties->shape_ink_rect = NULL;
   properties->shape_logical_rect = NULL;
@@ -6279,10 +6407,6 @@ pango_layout_get_item_properties (PangoItem      *item,
           properties->strikethrough = ((PangoAttrInt *)attr)->value;
           break;
 
-        case PANGO_ATTR_RISE:
-          properties->rise = ((PangoAttrInt *)attr)->value;
-          break;
-
         case PANGO_ATTR_LETTER_SPACING:
           properties->letter_spacing = ((PangoAttrInt *)attr)->value;
           break;
@@ -7110,8 +7234,6 @@ pango_layout_iter_get_cluster_extents (PangoLayoutIter *iter,
                                        PangoRectangle  *ink_rect,
                                        PangoRectangle  *logical_rect)
 {
-  ItemProperties properties;
-
   if (ITER_IS_INVALID (iter))
     return;
 
@@ -7124,8 +7246,6 @@ pango_layout_iter_get_cluster_extents (PangoLayoutIter *iter,
       return;
     }
 
-  pango_layout_get_item_properties (iter->run->item, &properties);
-
   pango_glyph_string_extents_range (iter->run->glyphs,
                                     iter->cluster_start,
                                     iter->next_cluster_glyph,
@@ -7136,7 +7256,7 @@ pango_layout_iter_get_cluster_extents (PangoLayoutIter *iter,
   if (ink_rect)
     {
       ink_rect->x += iter->cluster_x;
-      ink_rect->y -= properties.rise;
+      ink_rect->y -= iter->run->y_offset;
       offset_y (iter, &ink_rect->y);
     }
 
@@ -7144,7 +7264,7 @@ pango_layout_iter_get_cluster_extents (PangoLayoutIter *iter,
     {
       g_assert (logical_rect->width == iter->cluster_width);
       logical_rect->x += iter->cluster_x;
-      logical_rect->y -= properties.rise;
+      logical_rect->y -= iter->run->y_offset;
       offset_y (iter, &logical_rect->y);
     }
 }
@@ -7325,17 +7445,13 @@ pango_layout_iter_get_baseline (PangoLayoutIter *iter)
 int
 pango_layout_iter_get_run_baseline (PangoLayoutIter *iter)
 {
-  ItemProperties properties;
-
   if (ITER_IS_INVALID (iter))
     return 0;
 
   if (!iter->run)
     return iter->line_extents[iter->line_index].baseline;
 
-  pango_layout_get_item_properties (iter->run->item, &properties);
-
-  return iter->line_extents[iter->line_index].baseline - properties.rise;
+  return iter->line_extents[iter->line_index].baseline - iter->run->y_offset;
 }
 
 /**
diff --git a/pango/pango-markup.c b/pango/pango-markup.c
index a9df8ed0..65396547 100644
--- a/pango/pango-markup.c
+++ b/pango/pango-markup.c
@@ -1217,6 +1217,7 @@ span_parse_func     (MarkupData            *md G_GNUC_UNUSED,
   const char *strikethrough = NULL;
   const char *strikethrough_color = NULL;
   const char *rise = NULL;
+  const char *baseline_shift = NULL;
   const char *letter_spacing = NULL;
   const char *lang = NULL;
   const char *fallback = NULL;
@@ -1268,6 +1269,7 @@ span_parse_func     (MarkupData            *md G_GNUC_UNUSED,
 	CHECK_ATTRIBUTE2(background, "bgcolor");
         CHECK_ATTRIBUTE (background_alpha);
         CHECK_ATTRIBUTE2(background_alpha, "bgalpha");
+        CHECK_ATTRIBUTE(baseline_shift);
         break;
       case 'c':
 	CHECK_ATTRIBUTE2(foreground, "color");
@@ -1675,6 +1677,28 @@ span_parse_func     (MarkupData            *md G_GNUC_UNUSED,
       add_attribute (tag, pango_attr_rise_new (n));
     }
 
+  if (G_UNLIKELY (baseline_shift))
+    {
+      gint shift = 0;
+
+      if (span_parse_enum ("baseline_shift", baseline_shift, PANGO_TYPE_BASELINE_SHIFT, (int*)(void*)&shift, line_number, NULL))
+        add_attribute (tag, pango_attr_baseline_shift_new (shift));
+      else if (parse_length (baseline_shift, &shift) && (shift > 1024 || shift < -1024))
+        add_attribute (tag, pango_attr_baseline_shift_new (shift));
+      else
+        {
+          g_set_error (error,
+                       G_MARKUP_ERROR,
+                       G_MARKUP_ERROR_INVALID_CONTENT,
+                       _("Value of 'baseline_shift' attribute on <span> tag on line %d "
+                         "could not be parsed; should be 'superscript' or 'subscript' or "
+                         "an integer, or a string such as '5.5pt', not '%s'"),
+                       line_number, baseline_shift);
+          goto error;
+        }
+
+    }
+
   if (G_UNLIKELY (letter_spacing))
     {
       gint n = 0;
diff --git a/pango/pango-renderer.c b/pango/pango-renderer.c
index 055cdd97..231ebe7d 100644
--- a/pango/pango-renderer.c
+++ b/pango/pango-renderer.c
@@ -502,14 +502,10 @@ add_strikethrough (PangoRenderer    *renderer,
 
 static void
 get_item_properties (PangoItem       *item,
-                     gint            *rise,
                      PangoAttrShape **shape_attr)
 {
   GSList *l;
 
-  if (rise)
-    *rise = 0;
-
   if (shape_attr)
     *shape_attr = NULL;
 
@@ -524,11 +520,6 @@ get_item_properties (PangoItem       *item,
             *shape_attr = (PangoAttrShape *)attr;
           break;
 
-        case PANGO_ATTR_RISE:
-          if (rise)
-            *rise = ((PangoAttrInt *)attr)->value;
-          break;
-
         default:
           break;
         }
@@ -589,6 +580,7 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
   gboolean got_overall = FALSE;
   PangoRectangle overall_rect;
   const char *text;
+  int y_off;
 
   g_return_if_fail (PANGO_IS_RENDERER_FAST (renderer));
 
@@ -616,7 +608,6 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
   for (l = line->runs; l; l = l->next)
     {
       PangoFontMetrics *metrics;
-      gint rise;
       PangoLayoutRun *run = l->data;
       PangoAttrShape *shape_attr;
       PangoRectangle ink_rect, *ink = NULL;
@@ -627,7 +618,7 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
 
       pango_renderer_prepare_run (renderer, run);
 
-      get_item_properties (run->item, &rise, &shape_attr);
+      get_item_properties (run->item, &shape_attr);
 
       if (shape_attr)
         {
@@ -660,6 +651,8 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
 
       state.logical_rect_end = x + x_off + glyph_string_width;
 
+      y_off = run->y_offset;
+
       if (run->item->analysis.flags & PANGO_ANALYSIS_FLAG_CENTERED_BASELINE)
         {
           gboolean is_hinted = ((logical_rect.y | logical_rect.height) & (PANGO_SCALE - 1)) == 0;
@@ -668,7 +661,7 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
           if (is_hinted)
             adjustment = PANGO_UNITS_ROUND (adjustment);
 
-          rise += adjustment;
+          y_off += adjustment;
         }
 
 
@@ -690,14 +683,14 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
 
       if (shape_attr)
         {
-          draw_shaped_glyphs (renderer, run->glyphs, shape_attr, x + x_off, y - rise);
+          draw_shaped_glyphs (renderer, run->glyphs, shape_attr, x + x_off, y - y_off);
         }
       else
         {
           pango_renderer_draw_glyph_item (renderer,
                                           text,
                                           run,
-                                          x + x_off, y - rise);
+                                          x + x_off, y - y_off);
         }
 
       if (renderer->underline != PANGO_UNDERLINE_NONE ||
@@ -709,17 +702,17 @@ pango_renderer_draw_layout_line (PangoRenderer   *renderer,
 
           if (renderer->underline != PANGO_UNDERLINE_NONE)
             add_underline (renderer, &state,metrics,
-                           x + x_off, y - rise,
+                           x + x_off, y - y_off,
                            ink, logical);
 
           if (renderer->priv->overline != PANGO_OVERLINE_NONE)
             add_overline (renderer, &state,metrics,
-                           x + x_off, y - rise,
+                           x + x_off, y - y_off,
                            ink, logical);
 
           if (renderer->strikethrough)
             add_strikethrough (renderer, &state, metrics,
-                               x + x_off, y - rise,
+                               x + x_off, y - y_off,
                                ink, logical, run->glyphs->num_glyphs);
 
           pango_font_metrics_unref (metrics);
diff --git a/tests/test-itemize.c b/tests/test-itemize.c
index db6a715f..29f59210 100644
--- a/tests/test-itemize.c
+++ b/tests/test-itemize.c
@@ -77,6 +77,7 @@ affects_itemization (PangoAttribute *attr,
     case PANGO_ATTR_LETTER_SPACING:
     case PANGO_ATTR_SHAPE:
     case PANGO_ATTR_RISE:
+    case PANGO_ATTR_BASELINE_SHIFT:
     case PANGO_ATTR_LINE_HEIGHT:
     case PANGO_ATTR_ABSOLUTE_LINE_HEIGHT:
     case PANGO_ATTR_TEXT_TRANSFORM: