text layout: Avoid redundant text attributes

Don't insert text attributes if the font, or scale
or fallback did not actually change. This helps
Pango avoid excessive item breaks, which in turn
helps shaping to work across things like color
changes.

Related: https://gitlab.gnome.org/GNOME/pango/issues/28

diff --git a/gtk/gtktextlayout.c b/gtk/gtktextlayout.c
index f5dc11722b52912f9ddc6f17699f86ffc479e889..3196db22f8857c1cecd6b73805fcdc92649cd907 100644 (file)
--- a/gtk/gtktextlayout.c
+++ b/gtk/gtktextlayout.c
@@ -1641,32 +1641,62 @@ add_text_attrs (GtkTextLayout      *layout,
                 gint                byte_count,
                 PangoAttrList      *attrs,
                 gint                start,
-                gboolean            size_only)
+                gboolean            size_only,
+                PangoAttribute    **last_font_attr,
+                PangoAttribute    **last_scale_attr,
+                PangoAttribute    **last_fallback_attr)
 {
   PangoAttribute *attr;
 
-  attr = pango_attr_font_desc_new (style->font);
-  attr->start_index = start;
-  attr->end_index = start + byte_count;
+  if (*last_font_attr &&
+      pango_font_description_equal (style->font, ((PangoAttrFontDesc*)*last_font_attr)->desc) &&
+      (*last_font_attr)->end_index >= start)
+    {
+      (*last_font_attr)->start_index = MIN ((*last_font_attr)->start_index, start);
+      (*last_font_attr)->end_index = MAX ((*last_font_attr)->end_index, start + byte_count);
+    }
+  else
+    {
+      attr = pango_attr_font_desc_new (style->font);
+      attr->start_index = start;
+      attr->end_index = start + byte_count;
 
-  pango_attr_list_insert (attrs, attr);
+      pango_attr_list_insert (attrs, attr);
+      *last_font_attr = attr;
+    }
 
-  if (style->font_scale != 1.0)
+  if (*last_scale_attr &&
+      style->font_scale == ((PangoAttrFloat*)*last_scale_attr)->value &&
+      (*last_scale_attr)->end_index >= start)
+    {
+      (*last_scale_attr)->start_index = MIN ((*last_scale_attr)->start_index, start);
+      (*last_scale_attr)->end_index = MAX ((*last_scale_attr)->end_index, start + byte_count);
+    }
+  else if (style->font_scale != 1.0)
     {
       attr = pango_attr_scale_new (style->font_scale);
       attr->start_index = start;
       attr->end_index = start + byte_count;
 
       pango_attr_list_insert (attrs, attr);
+      *last_scale_attr = attr;
     }
 
-  if (style->no_fallback)
+  if (*last_fallback_attr &&
+      (!style->no_fallback) == ((PangoAttrInt*)*last_fallback_attr)->value &&
+      (*last_fallback_attr)->end_index >= start)
+    {
+      (*last_fallback_attr)->start_index = MIN ((*last_fallback_attr)->start_index, start);
+      (*last_fallback_attr)->end_index = MAX ((*last_fallback_attr)->end_index, start + byte_count);
+    }
+  else if (style->no_fallback)
     {
       attr = pango_attr_fallback_new (!style->no_fallback);
       attr->start_index = start;
       attr->end_index = start + byte_count;
 
       pango_attr_list_insert (attrs, attr);
+      *last_fallback_attr = attr;
     }
 
   if (style->letter_spacing != 0)
@@ -2269,7 +2299,10 @@ gtk_text_layout_get_line_display (GtkTextLayout *layout,
   gboolean initial_toggle_segments;
   gint h_margin;
   gint h_padding;
-  
+  PangoAttribute *last_font_attr = NULL;
+  PangoAttribute *last_scale_attr = NULL;
+  PangoAttribute *last_fallback_attr = NULL;
+
   g_return_val_if_fail (line != NULL, NULL);
 
   if (layout->one_display_cache)
@@ -2316,7 +2349,7 @@ gtk_text_layout_get_line_display (GtkTextLayout *layout,
       base_dir = (layout->keyboard_direction == GTK_TEXT_DIR_LTR) ?
         PANGO_DIRECTION_LTR : PANGO_DIRECTION_RTL;
     }
-  
+
   /* Allocate space for flat text for buffer
    */
   text_allocated = _gtk_text_line_byte_count (line);
@@ -2413,7 +2446,10 @@ gtk_text_layout_get_line_display (GtkTextLayout *layout,
                                      attrs, layout_byte_offset - bytes,
                                      size_only, TRUE);
                   add_text_attrs (layout, style, bytes, attrs,
-                                  layout_byte_offset - bytes, size_only);
+                                  layout_byte_offset - bytes, size_only,
+                                  &last_font_attr,
+                                  &last_scale_attr,
+                                  &last_fallback_attr);
                 }
               else if (seg->type == &gtk_text_texture_type)
                 {