1 files changed, 63 insertions, 0 deletions
diff --git a/libdimension/pattern/checker.c b/libdimension/pattern/checker.c
new file mode 100644
index 0000000..cce9623
--- /dev/null
+++ b/libdimension/pattern/checker.c
@@ -0,0 +1,63 @@
+/*************************************************************************
+ * Copyright (C) 2010-2014 Tavian Barnes <tavianator@tavianator.com>     *
+ *                                                                       *
+ * This file is part of The Dimension Library.                           *
+ *                                                                       *
+ * The Dimension 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 3 of the *
+ * License, or (at your option) any later version.                       *
+ *                                                                       *
+ * The Dimension 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 program.  If not, see                         *
+ * <http://www.gnu.org/licenses/>.                                       *
+ *************************************************************************/
+
+/**
+ * @file
+ * Checker pattern.
+ */
+
+#include "dimension/pattern.h"
+
+/// Checker pattern callback.
+static double
+dmnsn_checker_pattern_fn(const dmnsn_pattern *checker, dmnsn_vector v)
+{
+  double xmod = fmod(v.x, 2.0);
+  double ymod = fmod(v.y, 2.0);
+  double zmod = fmod(v.z, 2.0);
+
+  if (xmod < -dmnsn_epsilon)
+    xmod += 2.0;
+  if (ymod < -dmnsn_epsilon)
+    ymod += 2.0;
+  if (zmod < -dmnsn_epsilon)
+    zmod += 2.0;
+
+  // Return 0 when an even number of coordinates are in [0, 1), 1 otherwise
+  unsigned int n = 0;
+  if (xmod >= 1.0)
+    ++n;
+  if (ymod >= 1.0)
+    ++n;
+  if (zmod >= 1.0)
+    ++n;
+  return (n%2 == 0) ? 0.0 : 1.0;
+}
+
+/// The singleton instance.
+static dmnsn_pattern dmnsn_checker_instance = {
+  .pattern_fn = dmnsn_checker_pattern_fn,
+};
+
+dmnsn_pattern *
+dmnsn_new_checker_pattern(dmnsn_pool *pool)
+{
+  return &dmnsn_checker_instance;
+}