Bug 918 - Group doesn't clip if it's children are clipped

* clutter/cogl/common/cogl-clip-stack.h: 
	* clutter/cogl/common/cogl-clip-stack.c: Added functions to
	maintain a stack of clipping rectangles.

	* clutter/cogl/gles/cogl.c: 
	* clutter/cogl/gl/cogl.c: The cogl_clip_set and unset functions
	have moved into cogl-clip-stack.c which calls back to cogl.c to
	set the actual rectangles. Multiple clip rectangles are combined
	by merging the stencil buffers.

	* clutter/cogl/gles/cogl-primitives.c (_cogl_path_fill_nodes): 
	* clutter/cogl/gl/cogl-primitives.c (_cogl_path_fill_nodes): Merge
	the stencil buffer with the contents of the clipping stack after
	drawing the path.

	* clutter/cogl/gles/cogl-context.h (CoglContext): 
	* clutter/cogl/gl/cogl-context.h (CoglContext): Store the number
	of available stencil bits.

	* clutter/cogl/common/Makefile.am
	(libclutter_cogl_common_la_SOURCES): Added cogl-clip-stack.c

common/cogl-clip-stack.c

@@ -0,0 +1,180 @@
+/*
+ * Clutter COGL
+ *
+ * A basic GL/GLES Abstraction/Utility Layer
+ *
+ * Authored By Matthew Allum  <mallum@openedhand.com>
+ *
+ * Copyright (C) 2008 OpenedHand
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "cogl.h"
+#include "cogl-clip-stack.h"
+
+/* These are defined in the particular backend (float in GL vs fixed
+   in GL ES) */
+void _cogl_set_clip_planes (ClutterFixed x,
+			    ClutterFixed y,
+			    ClutterFixed width,
+			    ClutterFixed height);
+void _cogl_init_stencil_buffer (void);
+void _cogl_add_stencil_clip (ClutterFixed x,
+			     ClutterFixed y,
+			     ClutterFixed width,
+			     ClutterFixed height,
+			     gboolean     first);
+void _cogl_disable_clip_planes (void);
+void _cogl_disable_stencil_buffer (void);
+void _cogl_set_matrix (const ClutterFixed *matrix);
+
+typedef struct _CoglClipStackEntry CoglClipStackEntry;
+
+struct _CoglClipStackEntry
+{
+  /* The rectangle for this clip */
+  ClutterFixed        x_offset;
+  ClutterFixed        y_offset;
+  ClutterFixed        width;
+  ClutterFixed        height;
+
+  /* The matrix that was current when the clip was set */
+  ClutterFixed        matrix[16];
+};
+
+static GList *cogl_clip_stack_top = NULL;
+static GList *cogl_clip_stack_bottom = NULL;
+static int    cogl_clip_stack_depth = 0;
+
+static void
+_cogl_clip_stack_add (const CoglClipStackEntry *entry, int depth)
+{
+  int has_clip_planes = cogl_features_available (COGL_FEATURE_FOUR_CLIP_PLANES);
+
+  /* If this is the first entry and we support clip planes then use
+     that instead */
+  if (depth == 1 && has_clip_planes)
+    _cogl_set_clip_planes (entry->x_offset,
+			   entry->y_offset,
+			   entry->width,
+			   entry->height);
+  else
+    _cogl_add_stencil_clip (entry->x_offset,
+			    entry->y_offset,
+			    entry->width,
+			    entry->height,
+			    depth == (has_clip_planes ? 2 : 1));
+}
+
+void
+cogl_clip_set (ClutterFixed x_offset,
+	       ClutterFixed y_offset,
+	       ClutterFixed width,
+	       ClutterFixed height)
+{
+  CoglClipStackEntry *entry = g_slice_new (CoglClipStackEntry);
+
+  /* Make a new entry */
+  entry->x_offset = x_offset;
+  entry->y_offset = y_offset;
+  entry->width = width;
+  entry->height = height;
+
+  cogl_get_modelview_matrix (entry->matrix);
+
+  /* Add the entry to the current clip */
+  _cogl_clip_stack_add (entry, ++cogl_clip_stack_depth);
+
+  /* Store it in the stack */
+  cogl_clip_stack_top = g_list_prepend (cogl_clip_stack_top, entry);
+  if (cogl_clip_stack_bottom == NULL)
+    cogl_clip_stack_bottom = cogl_clip_stack_top;
+}
+
+void
+cogl_clip_unset (void)
+{
+  g_return_if_fail (cogl_clip_stack_top != NULL);
+
+  /* Remove the top entry from the stack */
+  g_slice_free (CoglClipStackEntry, cogl_clip_stack_top->data);
+  cogl_clip_stack_top = g_list_delete_link (cogl_clip_stack_top,
+					    cogl_clip_stack_top);
+  if (cogl_clip_stack_top == NULL)
+    cogl_clip_stack_bottom = NULL;
+  cogl_clip_stack_depth--;
+
+  /* Rebuild the clip */
+  _cogl_clip_stack_rebuild (FALSE);
+}
+
+void
+_cogl_clip_stack_rebuild (gboolean just_stencil)
+{
+  int has_clip_planes = cogl_features_available (COGL_FEATURE_FOUR_CLIP_PLANES);
+  GList *node;
+  int depth = 1;
+
+  /* Disable clip planes if the stack is empty */
+  if (has_clip_planes && cogl_clip_stack_depth < 1)
+    _cogl_disable_clip_planes ();
+
+  /* Disable the stencil buffer if there isn't enough entries */
+  if (cogl_clip_stack_depth < (has_clip_planes ? 2 : 1))
+    _cogl_disable_stencil_buffer ();
+
+  /* Re-add every entry from the bottom of the stack up */
+  for (node = cogl_clip_stack_bottom; node; node = node->prev, depth++)
+    if (!just_stencil || !has_clip_planes || depth > 1)
+      {
+	const CoglClipStackEntry *entry = (CoglClipStackEntry *) node->data;
+	cogl_push_matrix ();
+	_cogl_set_matrix (entry->matrix);
+	_cogl_clip_stack_add (entry, depth);
+	cogl_pop_matrix ();
+      }
+}
+
+void
+_cogl_clip_stack_merge (void)
+{
+  GList *node = cogl_clip_stack_bottom;
+
+  /* Merge the current clip stack on top of whatever is in the stencil
+     buffer */
+  if (node)
+    {
+      /* Skip the first entry if we have clipping planes */
+      if (cogl_features_available (COGL_FEATURE_FOUR_CLIP_PLANES))
+	node = node->prev;
+
+      while (node)
+	{
+	  const CoglClipStackEntry *entry = (CoglClipStackEntry *) node->data;
+	  cogl_push_matrix ();
+	  _cogl_set_matrix (entry->matrix);
+	  _cogl_clip_stack_add (entry, 3);
+	  cogl_pop_matrix ();
+
+	  node = node->prev;
+	}
+    }
+}