aabb: add expand call

Makefile.am

@@ -244,6 +244,7 @@ AM_LDFLAGS  += $(BOOST_LDFLAGS) $(BOOST_FILESYSTEM_LIB) $(BOOST_SYSTEM_LIB)
 AM_CXXFLAGS += -I$(top_srcdir)
 
 TEST_BIN = 			\
+    test/aabb			\
     test/backtrace 		\
     test/bezier			\
     test/bitwise		\

aabb.cpp

@@ -74,13 +74,58 @@ AABB<S,T>::closest (point<S,T> q) const
 }
 
 
+///////////////////////////////////////////////////////////////////////////////
+template <size_t S, typename T>
+AABB<S,T>&
+AABB<S,T>::expand (util::vector<S,T> mag)
+{
+    p0 -= mag / T{2};
+    p1 += mag / T{2};
+
+    return *this;
+}
+
+
 //-----------------------------------------------------------------------------
 template <size_t S, typename T>
 AABB<S,T>&
+AABB<S,T>::expand (T t)
+{
+    return expand (vector<S,T> {t});
+}
+
+
+//-----------------------------------------------------------------------------
+template <size_t S, typename T>
+AABB<S,T>
+AABB<S,T>::expanded (vector<S,T> mag)
+{
+    auto ret = *this;
+    ret.expand (mag);
+    return ret;
+}
+
+
+//-----------------------------------------------------------------------------
+template <size_t S, typename T>
+AABB<S,T>
+AABB<S,T>::expanded (T t)
+{
+    return expanded (vector<S,T> {t});
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+template <size_t S, typename T>
+AABB<S,T>&
 AABB<S,T>::contract (util::vector<S,T> mag)
 {
-    p0 -= mag / T{2};
+    // Avoid contracting magnitudes larger than our extent
-    p1 += mag / T{2};
+    auto diff = p1 - p0;
+    auto delta = min (diff, mag);
+
+    p0 += delta / T{2};
+    p1 -= delta / T{2};
 
     return *this;
 }

aabb.hpp

@@ -39,6 +39,11 @@ namespace util {
 
         point<S,T> closest (point<S,T>) const;
 
+        AABB<S,T>& expand (util::vector<S,T>);
+        AABB<S,T>& expand (T);
+        AABB<S,T>  expanded (util::vector<S,T>);
+        AABB<S,T>  expanded (T);
+
         AABB<S,T>& contract (util::vector<S,T>);
         AABB<S,T>& contract (T);
         AABB<S,T>  contracted (util::vector<S,T>) const;

test/aabb.cpp

@@ -0,0 +1,51 @@
+#include "aabb.hpp"
+
+int
+main (int, char**)
+{
+    {
+        // Test contraction
+        util::AABB2f box {
+            { 2, 2 },
+            { 8, 8 }
+        };
+
+        box.contract (2.f);
+
+        CHECK_EQ (box.p0.x, 3);
+        CHECK_EQ (box.p0.y, 3);
+        CHECK_EQ (box.p1.x, 7);
+        CHECK_EQ (box.p1.y, 7);
+    }
+
+    {
+        // Test expansion
+        util::AABB2f box {
+            { 2, 2 },
+            { 8, 8 }
+        };
+
+        box.expand (2.f);
+        
+        CHECK_EQ (box.p0.x, 1);
+        CHECK_EQ (box.p0.y, 1);
+        CHECK_EQ (box.p1.x, 9);
+        CHECK_EQ (box.p1.y, 9);
+    }
+
+
+    {
+        // Ensure we don't wrap-around on unsigned position types when contracting
+        util::AABB2f small {
+            { 0, 0 },
+            { 1, 1 }
+        };
+
+        small.contract (10);
+
+        CHECK_EQ (small.p0.x, 0.5f);
+        CHECK_EQ (small.p0.y, 0.5f);
+        CHECK_EQ (small.p1.x, 0.5f);
+        CHECK_EQ (small.p1.y, 0.5f);
+    }
+}