adding explosion stuff, adding trace file.

game/state/explosion.hpp

@@ -1,17 +1,28 @@
 #pragma once
 
-#if 0
+/**
+ * Explosion: just an effect which looks good.
+ */
 class Explosion {
 public:
     enum class Kind {
-        Normal,
-        MissileWithShip
+        MissileExplodesInSpace, // missile explode in free space
+        MissileAgainstPlanet,   // explosion of missile when it hits a planet
+        MissileAgainstShip      // bigger explosion: missile hits a ship which explodes with it
     };
 
-    glm::vec2 position;
+    Explosion(const glm::vec2 &pos, Kind kind, float maxAge=1.0)
+        : position(pos), kind(kind), age(0.0), maxAge(maxAge)
+    {
+    }
 
-    Explosion(Kind kind);
+    const Kind      kind;     // kind of the explosion
+    const glm::vec2 position; // position where it starts
+    float           age;      // age (in seconsd) of the explosion
 
-public:
+    // age (in seconds) when the explosion is not visible
+    // anymore and will disappear afterwards
+    const float     maxAge;
 };
+
 #endif