Support layer and interaction transparancy. Refs #1

src/fmri/Animation.hpp

@@ -1,6 +1,8 @@
 #pragma once
 
 
+#include "utils.hpp"
+
 namespace fmri
 {
     class Animation
@@ -10,5 +12,21 @@ namespace fmri
 
         virtual void draw(float step) = 0;
 
+    private:
+        static float getAlpha();
+
+    protected:
+        template<typename It>
+        void patchTransparancy(It begin, It end)
+        {
+            if constexpr (std::tuple_size<Color>::value >= 4) {
+                const auto alpha = getAlpha();
+                for (; begin != end; ++begin) {
+                    Color &color = *begin;
+                    color[3] = alpha;
+                }
+            }
+        }
+
     };
 }