Track changes in layout and dependencies via serials

We track changes in the PangoContext and automatically call
pango_layout_context_changed() when needed, plus we track
changes in the layout and let apps know via pango_layout_get_serial
when the layout changed and needs to be redrawn.

https://bugzilla.gnome.org/show_bug.cgi?id=340066

7 files changed, 91 insertions, 19 deletions

diff --git a/docs/pango-sections.txt b/docs/pango-sections.txt
index ec004bdc..f22eadf1 100644
--- a/docs/pango-sections.txt
+++ b/docs/pango-sections.txt
@@ -443,6 +443,7 @@ pango_layout_copy
 
 pango_layout_get_context
 pango_layout_context_changed
+pango_layout_get_serial
 
 pango_layout_set_text
 pango_layout_get_text
diff --git a/docs/tmpl/layout.sgml b/docs/tmpl/layout.sgml
index 997507df..e0a6ebf4 100644
--- a/docs/tmpl/layout.sgml
+++ b/docs/tmpl/layout.sgml
@@ -100,6 +100,15 @@ has no user-visible fields.
 @layout: 
 
 
+<!-- ##### FUNCTION pango_layout_get_serial ##### -->
+<para>
+
+</para>
+
+@layout: 
+@Returns: 
+
+
 <!-- ##### FUNCTION pango_layout_set_text ##### -->
 <para>
 
diff --git a/pango/pango-context.c b/pango/pango-context.c
index 0477a957..b15f44d1 100644
--- a/pango/pango-context.c
+++ b/pango/pango-context.c
@@ -108,7 +108,6 @@ pango_context_finalize (GObject *object)
   G_OBJECT_CLASS (pango_context_parent_class)->finalize (object);
 }
 
-
 /**
  * pango_context_new:
  *
diff --git a/pango/pango-layout-private.h b/pango/pango-layout-private.h
index dc4f3d4c..d0bf93eb 100644
--- a/pango/pango-layout-private.h
+++ b/pango/pango-layout-private.h
@@ -46,6 +46,9 @@ struct _PangoLayout
   /* Value fields.  These will be memcpy'd in _copy() */
   int copy_begin;
 
+  guint serial;
+  guint context_serial;
+
   int length;			/* length of text in bytes */
   int n_chars;		        /* number of characters in layout */
   int width;			/* wrap/ellipsize width, in device units, or -1 if not set */
diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index 48168d82..b1f63461 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -155,6 +155,9 @@ check_invalid (PangoLayoutIter *iter,
 }
 #endif
 
+static void check_context_changed  (PangoLayout *layout);
+static void layout_changed  (PangoLayout *layout);
+
 static void pango_layout_clear_lines (PangoLayout *layout);
 static void pango_layout_check_lines (PangoLayout *layout);
 
@@ -188,6 +191,7 @@ G_DEFINE_TYPE (PangoLayout, pango_layout, G_TYPE_OBJECT)
 static void
 pango_layout_init (PangoLayout *layout)
 {
+  layout->serial = 1;
   layout->attrs = NULL;
   layout->font_desc = NULL;
   layout->text = NULL;
@@ -269,6 +273,7 @@ pango_layout_new (PangoContext *context)
   layout = g_object_new (PANGO_TYPE_LAYOUT, NULL);
 
   layout->context = context;
+  layout->context_serial = pango_context_get_serial (context);
   g_object_ref (context);
 
   return layout;
@@ -346,10 +351,13 @@ pango_layout_set_width (PangoLayout *layout,
 {
   g_return_if_fail (layout != NULL);
 
+  if (width < 0)
+    width = -1;
+
   if (width != layout->width)
     {
       layout->width = width;
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -418,7 +426,7 @@ pango_layout_set_height (PangoLayout *layout,
       if (layout->ellipsize != PANGO_ELLIPSIZE_NONE &&
 	  !(layout->lines && layout->is_ellipsized == FALSE &&
 	    height < 0 && layout->line_count <= (guint) -height))
-	pango_layout_clear_lines (layout);
+	layout_changed (layout);
     }
 }
 
@@ -461,7 +469,7 @@ pango_layout_set_wrap (PangoLayout  *layout,
       layout->wrap = wrap;
 
       if (layout->width != -1)
-	pango_layout_clear_lines (layout);
+	layout_changed (layout);
     }
 }
 
@@ -532,7 +540,7 @@ pango_layout_set_indent (PangoLayout *layout,
   if (indent != layout->indent)
     {
       layout->indent = indent;
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -569,7 +577,7 @@ pango_layout_set_spacing (PangoLayout *layout,
   if (spacing != layout->spacing)
     {
       layout->spacing = spacing;
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -612,7 +620,8 @@ pango_layout_set_attributes (PangoLayout   *layout,
   layout->attrs = attrs;
   if (layout->attrs)
     pango_attr_list_ref (layout->attrs);
-  pango_layout_clear_lines (layout);
+
+  layout_changed (layout);
 
   if (old_attrs)
     pango_attr_list_unref (old_attrs);
@@ -659,7 +668,7 @@ pango_layout_set_font_description (PangoLayout                 *layout,
 
       layout->font_desc = desc ? pango_font_description_copy (desc) : NULL;
 
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
       layout->tab_width = -1;
     }
 }
@@ -710,7 +719,7 @@ pango_layout_set_justify (PangoLayout *layout,
       layout->justify = justify;
 
       if (layout->is_ellipsized || layout->is_wrapped)
-	pango_layout_clear_lines (layout);
+	layout_changed (layout);
     }
 }
 
@@ -766,7 +775,7 @@ pango_layout_set_auto_dir (PangoLayout *layout,
   if (auto_dir != layout->auto_dir)
     {
       layout->auto_dir = auto_dir;
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -808,7 +817,7 @@ pango_layout_set_alignment (PangoLayout   *layout,
   if (alignment != layout->alignment)
     {
       layout->alignment = alignment;
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -853,7 +862,7 @@ pango_layout_set_tabs (PangoLayout   *layout,
 
       layout->tabs = tabs ? pango_tab_array_copy (tabs) : NULL;
 
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -900,8 +909,7 @@ pango_layout_set_single_paragraph_mode (PangoLayout *layout,
   if (layout->single_paragraph != setting)
     {
       layout->single_paragraph = setting;
-
-      pango_layout_clear_lines (layout);
+      layout_changed (layout);
     }
 }
 
@@ -952,7 +960,7 @@ pango_layout_set_ellipsize (PangoLayout        *layout,
       layout->ellipsize = ellipsize;
 
       if (layout->is_ellipsized || layout->is_wrapped)
-	pango_layout_clear_lines (layout);
+	layout_changed (layout);
     }
 }
 
@@ -1073,7 +1081,7 @@ pango_layout_set_text (PangoLayout *layout,
 
   layout->n_chars = pango_utf8_strlen (layout->text, -1);
 
-  pango_layout_clear_lines (layout);
+  layout_changed (layout);
 
   g_free (old_text);
 }
@@ -1247,6 +1255,26 @@ pango_layout_get_unknown_glyphs_count (PangoLayout *layout)
     return count;
 }
 
+static void
+check_context_changed (PangoLayout *layout)
+{
+  int old_serial = layout->context_serial;
+
+  layout->context_serial = pango_context_get_serial (layout->context);
+
+  if (old_serial != layout->context_serial)
+    pango_layout_context_changed (layout);
+}
+
+static void
+layout_changed (PangoLayout *layout)
+{
+  layout->serial++;
+  if (layout->serial == 0)
+    layout->serial++;
+  pango_layout_clear_lines (layout);
+}
+
 /**
  * pango_layout_context_changed:
  * @layout: a #PangoLayout
@@ -1259,11 +1287,39 @@ pango_layout_get_unknown_glyphs_count (PangoLayout *layout)
 void
 pango_layout_context_changed (PangoLayout *layout)
 {
-  pango_layout_clear_lines (layout);
+  g_return_if_fail (PANGO_IS_LAYOUT (layout));
+
+  layout_changed (layout);
   layout->tab_width = -1;
 }
 
 /**
+ * pango_layout_get_serial:
+ * @layout: a #PangoLayout
+ *
+ * Returns the current serial number of @layout.  The serial number is
+ * initialized to an small number  larger than zero when a new layout
+ * is created and is increased whenever the layout is changed using any
+ * of the setter functions, or the #PangoContext it uses has changed.
+ * The serial may wrap, but will never have the value 0. Since it
+ * can wrap, never compare it with "less than", always use "not equals".
+ *
+ * This can be used to automatically detect changes to a #PangoLayout, and
+ * is useful for example to decide whether a layout needs redrawing.
+ * To force the serial to be increased, use pango_layout_context_changed().
+ *
+ * Return value: The current serial number of @layout.
+ *
+ * Since: 1.32.4
+ **/
+guint
+pango_layout_get_serial (PangoLayout *layout)
+{
+  check_context_changed (layout);
+  return layout->serial;
+}
+
+/**
  * pango_layout_get_log_attrs:
  * @layout: a #PangoLayout
  * @attrs: (out)(array length=n_attrs)(transfer container):
@@ -2475,6 +2531,8 @@ pango_layout_get_extents_internal (PangoLayout    *layout,
 
   g_return_if_fail (layout != NULL);
 
+  pango_layout_check_lines (layout);
+
   if (ink_rect && layout->ink_rect_cached)
     {
       *ink_rect = layout->ink_rect;
@@ -2488,8 +2546,6 @@ pango_layout_get_extents_internal (PangoLayout    *layout,
   if (!ink_rect && !logical_rect && !line_extents)
     return;
 
-  pango_layout_check_lines (layout);
-
   /* When we are not wrapping, we need the overall width of the layout to
    * figure out the x_offsets of each line. However, we only need the
    * x_offsets if we are computing the ink_rect or individual line extents.
@@ -3799,6 +3855,8 @@ pango_layout_check_lines (PangoLayout *layout)
   PangoDirection prev_base_dir = PANGO_DIRECTION_NEUTRAL, base_dir = PANGO_DIRECTION_NEUTRAL;
   ParaBreakState state;
 
+  check_context_changed (layout);
+
   if (G_LIKELY (layout->lines))
     return;
 
diff --git a/pango/pango-layout.h b/pango/pango-layout.h
index 6bc50a6a..8177612c 100644
--- a/pango/pango-layout.h
+++ b/pango/pango-layout.h
@@ -163,6 +163,7 @@ gboolean           pango_layout_is_ellipsized (PangoLayout        *layout);
 int      pango_layout_get_unknown_glyphs_count (PangoLayout    *layout);
 
 void     pango_layout_context_changed (PangoLayout    *layout);
+guint    pango_layout_get_serial      (PangoLayout    *layout);
 
 void     pango_layout_get_log_attrs (PangoLayout    *layout,
 				     PangoLogAttr  **attrs,
diff --git a/pango/pango.def b/pango/pango.def
index 3b4252f3..77098e75 100644
--- a/pango/pango.def
+++ b/pango/pango.def
@@ -255,6 +255,7 @@ EXPORTS
 	pango_layout_get_log_attrs_readonly
 	pango_layout_get_pixel_extents
 	pango_layout_get_pixel_size
+	pango_layout_get_serial
 	pango_layout_get_single_paragraph_mode
 	pango_layout_get_size
 	pango_layout_get_spacing