cogl: Adds _cogl_util_point_in_polygon API

This adds a utility function that can determine if a given point
intersects an arbitrary polygon, by counting how many edges a
"semi-infinite" horizontal ray crosses from that point. The plan is to
use this for a software based read-pixel fast path that avoids using the
GPU to rasterize journaled primitives and can instead intersect a point
being read with quads in the journal to determine the correct color.

cogl/Makefile.am

@@ -269,6 +269,8 @@ cogl_sources_c = \
 	$(srcdir)/cogl-callback-list.h                  \
 	$(srcdir)/cogl-callback-list.c                  \
 	$(srcdir)/cogl-gtype-private.h                  \
+	$(srcdir)/cogl-point-in-poly-private.h       \
+	$(srcdir)/cogl-point-in-poly.c       	\
 	$(NULL)
 
 if SUPPORT_XLIB

cogl/cogl-point-in-poly-private.h

@@ -0,0 +1,40 @@
+/*
+ * Cogl
+ *
+ * An object oriented GL/GLES Abstraction/Utility Layer
+ *
+ * Copyright (C) 2011 Intel Corporation.
+ *
+ * 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, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __COGL_POINT_INT_POLYGON_PRIVATE_H
+#define __COGL_POINT_INT_POLYGON_PRIVATE_H
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+int
+_cogl_util_point_in_poly (float point_x,
+                          float point_y,
+                          void *vertices,
+                          size_t stride,
+                          int n_vertices);
+
+G_END_DECLS
+
+#endif /* __COGL_POINT_INT_POLYGON_PRIVATE_H */
+

cogl/cogl-point-in-poly.c

@@ -0,0 +1,69 @@
+/*
+ * Point Inclusion in Polygon Test
+ *
+ * Copyright (c) 1970-2003, Wm. Randolph Franklin
+ * Copyright (C) 2011 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimers.
+ *    2. Redistributions in binary form must reproduce the above
+ *    copyright notice in the documentation and/or other materials
+ *    provided with the distribution.
+ * 3. The name of W. Randolph Franklin may not be used to endorse or
+ *    promote products derived from this Software without specific
+ *    prior written permission.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * Note:
+ * The algorithm for this point_in_poly() function was learnt from:
+ * http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <glib.h>
+
+int
+_cogl_util_point_in_poly (float point_x,
+                          float point_y,
+                          void *vertices,
+                          size_t stride,
+                          int n_vertices)
+{
+  int i, j, c = 0;
+
+  for (i = 0, j = n_vertices - 1; i < n_vertices; j = i++)
+    {
+      float vert_xi = *(float *)((guint8 *)vertices + i * stride);
+      float vert_xj = *(float *)((guint8 *)vertices + j * stride);
+      float vert_yi = *(float *)((guint8 *)vertices + i * stride +
+                                 sizeof (float));
+      float vert_yj = *(float *)((guint8 *)vertices + j * stride +
+                                 sizeof (float));
+
+      if (((vert_yi > point_y) != (vert_yj > point_y)) &&
+           (point_x < (vert_xj - vert_xi) * (point_y - vert_yi) /
+            (vert_yj - vert_yi) + vert_xi) )
+         c = !c;
+    }
+
+  return c;
+}
+