expose an indexing operator on box2d to allow for easy pythonic access to bounds parts

bindings/python/mapnik_envelope.cpp

@@ -231,6 +231,7 @@ void export_envelope()
         .def(self * float()) // __mult__
         .def(float() * self) 
         .def(self / float()) // __div__
+        .def("__getitem__",&box2d<double>::operator[])
         .def_pickle(envelope_pickle_suite())
         ;
 }

include/mapnik/box2d.hpp

@@ -85,6 +85,7 @@ public:
     box2d_type& operator-=(box2d_type const& other);
     box2d_type& operator*=(T);
     box2d_type& operator/=(T);
+    T operator[](int index) const;
 };
     
 template <class charT,class traits,class T>

src/box2d.cpp

@@ -23,6 +23,9 @@
 
 #include <mapnik/box2d.hpp>
 
+// stl
+#include <stdexcept>
+
 namespace mapnik
 {
 template <typename T>
@@ -340,6 +343,32 @@ box2d<T>& box2d<T>::operator/=(T t)
     return *this;
 }
 
+template <typename T>    
+T box2d<T>::operator[] (int index) const
+{
+    switch(index)
+    {
+    case 0:
+        return minx_;
+    case 1:
+        return miny_;
+    case 2:
+        return maxx_;
+    case 3:
+        return maxy_;
+    case -4:
+        return minx_;
+    case -3:
+        return miny_;
+    case -2:
+        return maxx_;
+    case -1:
+        return maxy_;
+    default:
+        throw std::out_of_range("index out of range, max value is 3, min value is -4 ");
+    }
+}
+    
 template class box2d<int>;
 template class box2d<double>;
 }

tests/python_tests/object_test.py

@@ -483,6 +483,15 @@ def test_envelope_init():
     eq_(e.maxx, 200)
     eq_(e.maxy, 200)
     
+    eq_(e[0],100)
+    eq_(e[1],100)
+    eq_(e[2],200)
+    eq_(e[3],200)
+    eq_(e[0],e[-4])
+    eq_(e[1],e[-3])
+    eq_(e[2],e[-2])
+    eq_(e[3],e[-1])
+    
     c = e.center()
 
     eq_(c.x, 150)