Hackish proof of concept patch to fix the flashing on dnd.

The flashing is due to the fact that we get the expose event between the
two modifications caused by the dnd: that causes update_highlighting_cb
to be called, which in turn calls ensure_hilight.

My idea is to synchrounously process all the pending modifications in the
queue which affect the exposed area. The sync process should not be that
bad since the exposed area is small and at least we avoid redrawing for
each modification. If the sync process turns out to be a problem we should
probably do it for a timeslice and if it doesn't suffice for all the
modifications in the area, live with a bit of flickering.

The implementation is hackish because:
a) I hate async_modify and even more I hate running it in a while(). My hate
   will increase even more if we introduce yet another timeslice timer.
b) Instead of 'peeking' at the head of the queue I simply pop and process one
   extra modification.


Seems to work though.


diff -r 41940e78acc6 gtksourceview/gtksourcecontextengine.c
--- a/gtksourceview/gtksourcecontextengine.c	Tue May 30 13:34:31 2006
+++ b/gtksourceview/gtksourcecontextengine.c	Wed May 31 11:42:14 2006
@@ -436,7 +436,8 @@
 static void	 text_modified			(GtkSourceContextEngine		*ce,
 						 gint				 offset,
 						 gint				 delta);
-static gboolean	 async_modify			(GtkSourceContextEngine		*ce);
+static gboolean	 async_modify			(GtkSourceContextEngine		*ce,
+						 gint				 until);
 static void	 update_syntax			(GtkSourceContextEngine		*ce,
 						 const GtkTextIter		*needed_end,
 						 Modify				*modify);
@@ -589,6 +590,8 @@
 		     const GtkTextIter      *end,
 		     gboolean                synchronous)
 {
+	gint end_offset;
+
 	g_return_if_fail (GTK_IS_SOURCE_CONTEXT_ENGINE (ce));
 	g_return_if_fail (start != NULL);
        	g_return_if_fail (end != NULL);
@@ -596,9 +599,13 @@
 	if (!ce->priv->highlight)
 		return;
 
+	end_offset = gtk_text_iter_get_offset (end);
 	if (ce->priv->worker_last_offset < 0 ||
-	    ce->priv->worker_last_offset >= gtk_text_iter_get_offset (end))
-	{
+	    ce->priv->worker_last_offset >= end_offset)
+	{
+		/* try to process synchronously all the pending
+		   modifications in this area to avoid fliker */
+		while (async_modify (ce, end_offset)) ;
 		ensure_highlighted (ce, start, end);
 	}
 	else
@@ -606,7 +613,7 @@
 		if (synchronous)
 		{
 			/* Do pending asynchronous modifications. */
-			while (async_modify (ce)) ;
+			while (async_modify (ce, -1)) ;
 			update_syntax (ce, end, NULL);
 			ensure_highlighted (ce, start, end);
 		}
@@ -1725,7 +1732,7 @@
 	{
 		GTimer *timer = g_timer_new ();
 
-		while (async_modify (ce))
+		while (async_modify (ce, -1))
 		{
 			if (g_timer_elapsed (timer, NULL) * 1000. > WORKER_TIME_SLICE)
 				break;
@@ -2314,14 +2321,19 @@
  * queue is empty.
  */
 static gboolean
-async_modify (GtkSourceContextEngine *ce)
+async_modify (GtkSourceContextEngine *ce, gint until)
 {
 	Modify *modify;
+	gboolean ret = TRUE;
 
 	modify = modify_queue_pop (ce->priv->modifications);
 
 	if (modify == NULL)
 		return FALSE;
+
+	/* (hack) for now process this mod anyway since we popped it */
+	if (until != -1 && modify->offset > until)
+		ret = FALSE;
 
 	update_syntax (ce, NULL, modify);
 
@@ -2331,7 +2343,7 @@
 		modify_queue_clear_by_offset (ce->priv->modifications,
 					      ce->priv->worker_last_offset);
 
-	return TRUE;
+	return ret;
 }
 
 /**