Support layer and interaction transparancy. Refs #1

src/fmri/LayerVisualisation.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <vector>
+#include "utils.hpp"
 
 namespace fmri
 {
@@ -19,10 +20,25 @@ namespace fmri
         virtual void render() = 0;
         virtual const std::vector<float>& nodePositions() const;
 
+    private:
+        static float getAlpha();
+
     protected:
         std::vector<float> nodePositions_;
 
         template<Ordering Order>
         void initNodePositions(size_t n, float spacing);
+
+        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;
+                }
+            }
+        }
     };
 }