nebula.m

        if (nebula.armorRegen > 0 || nebula.shieldRegen > 0) {
          // positive nebula
          currentShields += nebula.shieldRegen;
          currentArmor   += nebula.armorRegen;
          
          if (currentArmor > maxArmor && currentArmor > 0.0) currentArmor = maxArmor;
          if (currentShields > maxShields) currentShields = maxShields;
        } else {
          // negative nebula
          [self damageShields:-nebula.shieldRegen armor:-nebula.armorRegen];
        }