From 1d1dcc875a8dcf55cb550f06f611f610710fd354 Mon Sep 17 00:00:00 2001
From: David Williams <david@david-williams.info>
Date: Mon, 14 Jan 2013 23:13:17 +0100
Subject: [PATCH] Added 'intersects' function to Region.

---
 .../PolyVoxCore/include/PolyVoxCore/Region.h  |  2 ++
 library/PolyVoxCore/source/Region.cpp         | 25 ++++++++++++++-----
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/library/PolyVoxCore/include/PolyVoxCore/Region.h b/library/PolyVoxCore/include/PolyVoxCore/Region.h
index d65fb022..32aa7715 100644
--- a/library/PolyVoxCore/include/PolyVoxCore/Region.h
+++ b/library/PolyVoxCore/include/PolyVoxCore/Region.h
@@ -207,6 +207,8 @@ namespace PolyVox
 		int32_t m_iUpperZ;
 	};
 
+	bool intersects(const Region& a, const Region& b);
+
 	// Functions to be inlined to to be in the header rather than the .cpp.
 	// 'inline' keyword is used for the definition rather than the declaration.
 	// See also http://www.parashift.com/c++-faq-lite/inline-functions.html
diff --git a/library/PolyVoxCore/source/Region.cpp b/library/PolyVoxCore/source/Region.cpp
index dee56bb3..b3512b6f 100644
--- a/library/PolyVoxCore/source/Region.cpp
+++ b/library/PolyVoxCore/source/Region.cpp
@@ -148,12 +148,12 @@ namespace PolyVox
 			&&  (m_iUpperX == rhs.m_iUpperX) && (m_iUpperY == rhs.m_iUpperY) && (m_iUpperZ == rhs.m_iUpperZ));
     }
 
-	////////////////////////////////////////////////////////////////////////////////
-	/// Two regions are considered different if any of their extents differ.
-	/// \param rhs The Region to compare to.
-    /// \return true if the Regions are different.
-    /// \sa operator==
-	////////////////////////////////////////////////////////////////////////////////
+	/**
+	 *  Two regions are considered different if any of their extents differ.
+	 *  \param rhs The Region to compare to.
+     *  \return true if the Regions are different.
+     *  \sa operator==
+	 */
     bool Region::operator!=(const Region& rhs) const
     {
 		return !(*this == rhs);
@@ -468,4 +468,17 @@ namespace PolyVox
 	{
 		shrink(v3dAmount.getX(), v3dAmount.getY(), v3dAmount.getZ());
 	}
+	/**
+	 * This function only returns true if the regions are really intersecting and not simply touching.
+	 */
+	bool intersects(const Region& a, const Region& b)
+	{
+		// No intersection if seperated along an axis.
+		if(a.getUpperX() < b.getLowerX() || a.getLowerX() > b.getUpperX()) return false;
+		if(a.getUpperY() < b.getLowerY() || a.getLowerY() > b.getUpperY()) return false;
+		if(a.getUpperZ() < b.getLowerZ() || a.getLowerZ() > b.getUpperZ()) return false;
+
+		// Overlapping on all axes means Regions are intersecting.
+		return true;
+	}
 }