Improve the derivative class for hermites. Compare http://synfig.org/images/a/a8...

[synfig.git] / ETL / trunk / ETL / _calculus.h

diff --git a/ETL/trunk/ETL/_calculus.h b/ETL/trunk/ETL/_calculus.h
index 279ed91..9fbea85 100644 (file)
--- a/ETL/trunk/ETL/_calculus.h
+++ b/ETL/trunk/ETL/_calculus.h
@@ -28,6 +28,8 @@
 
 #include <functional>
 
+#include "hermite"
+
 /* === M A C R O S ========================================================= */
 
 //#ifndef _EPSILON
@@ -56,6 +58,22 @@ public:
 };
 
 template <typename T>
+class derivative<hermite<T> > : public std::unary_function<typename hermite<T>::argument_type,typename hermite<T>::result_type>
+{
+       hermite<T> func;
+public:
+       explicit derivative(const hermite<T> &x):func(x) { }
+
+       typename hermite<T>::result_type
+       operator()(const typename hermite<T>::argument_type &x)const
+       {
+               T a = func[0], b = func[1], c = func[2], d = func[3];
+               typename hermite<T>::argument_type y(1-x);
+               return ((b-a)*y*y + (c-b)*x*y*2 + (d-c)*x*x) * 3;
+       }
+};
+
+template <typename T>
 class integral : public std::binary_function<typename T::argument_type,typename T::argument_type,typename T::result_type>
 {
        T func;