added trace implemention

game/state/trace.cpp

@@ -0,0 +1,22 @@
+#include "trace.hpp"
+
+#include <glm/gtx/norm.hpp>
+
+#include "missile.hpp"
+
+namespace game {
+    Trace::TracePoint::TracePoint(const Missile *missile)
+        : position(missile->position), speed(glm::length(missile->velocity))
+    {
+    }
+
+    Trace::Trace(const Missile *missile)
+    {
+        points.push_back(TracePoint(missile));
+    }
+
+    void Trace::addPointFromMissile(const Missile *missile)
+    {
+        points.push_back(TracePoint(missile));
+    }
+}

game/state/trace.hpp

@@ -1,24 +1,34 @@
 #pragma once
 
 #include <glm/vec2.hpp>
+#include <vector>
 
 namespace game {
+    class Missile;
+
     /*
      * Trace of a missile through the space.
      * Useful for rendering sth. like a smoke trail to follow the rocket.
      */
     class Trace {
         public:
-            Trace(const glm::vec2 &startPoint)
-            {
-                points.push_back(startPoint);
-            }
+            Trace(const Missile *missile);
 
-            void addPoint(const glm::vec2 &p)
-            {
-                points.push_back(p);
-            }
+            // TODO: add velocity of the rocket or age at the points too becasue
+            // that enables nice rendering of speed etc. at different points
+            // TODO: give missile to this
+            void addPointFromMissile(const Missile *missile);
 
-            std::vector<glm::vec2> points;
+            /*
+             * Trace point data to be used when rendering.
+             */
+            struct TracePoint {
+                TracePoint(const Missile *missile);
+
+                const glm::vec2 position;
+                const float     speed;
+            };
+
+            std::vector<TracePoint> points;
     };
 }