Mark Arabic text as 'needs offscreen'

Arabic is a cursive script, and regularly has
overlapping contours between glyphs, which will
cause ugly artifacts when rendererd with translucency,
unless we use an offscreen.

gsk/gskrendernodeimpl.c

@@ -5607,6 +5607,13 @@ gsk_text_node_new (PangoFont              *font,
       if (glyphs->glyphs[i].attr.is_color)
         self->has_color_glyphs = TRUE;
 
+      if (i == 0 &&
+          (*(guint*)(&glyphs->glyphs[i].attr)) & (1 << 3))
+        {
+          g_print ("text node in Arabic\n");
+          node->offscreen_for_opacity = TRUE;
+        }
+
       n++;
     }
 

gsk/gskrendernodeparser.c

@@ -1020,6 +1020,11 @@ parse_glyphs (GtkCssParser *parser,
                 gi.attr.is_color = 1;
               else
                 gi.attr.is_color = 0;
+
+              if (gtk_css_parser_try_ident (parser, "need-offscreen"))
+                *((guint *)&gi.attr) |= (1 << 3);
+              else
+                *((guint *)&gi.attr) &= ~(1 << 3);
             }
 
           pango_glyph_string_set_size (glyph_string, glyph_string->num_glyphs + 1);
@@ -3288,6 +3293,8 @@ gsk_text_node_serialize_glyphs (GskRenderNode *node,
             g_string_append (p, " same-cluster");
           if (glyphs[i].attr.is_color)
             g_string_append (p, " color");
+          if ((*(guint*)&glyphs[i].attr) & (1 << 3))
+            g_string_append (p, " needs-offscreen");
         }
 
       if (i + 1 < n_glyphs)

gtk/gskpango.c

@@ -97,6 +97,14 @@ gsk_pango_renderer_draw_glyph_item (PangoRenderer  *renderer,
   GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
   GdkRGBA color;
 
+  if (glyph_item->item->analysis.script == PANGO_SCRIPT_ARABIC)
+    {
+      g_print ("glyph item in arabic!\n");
+      *(guint*)&(glyph_item->glyphs->glyphs[0].attr) |= (1 << 3);
+    }
+  else
+    *(guint*)&(glyph_item->glyphs->glyphs[0].attr) &= ~(1 << 3);
+
   get_color (crenderer, PANGO_RENDER_PART_FOREGROUND, &color);
 
   gtk_snapshot_append_text (crenderer->snapshot,