Funny little game 
Thank you ! I'm glad you tried and enjoyed it, thank you for your feedback, here are my answers :
Sometimes the enemies spawn almost inside or directly behind the player, where you have no chance to evade. Don't you want to let them enter from the border of the screen?
Well i don't know, i see what you mean but i like the effect of surprise and this behavior adds some "luck" parameter to your final score, which is good in any game (skills+a touch of luck = success)
EDIT : spawning enemies outside the window add a little extra immersion i like it !
There's a bug when you stand still: an enemy tank drives over you and is too close to hit you.
Yes i think i have to stop the enemy before he reaches the player.
At the moment, you can keep firing all the time. There should be a motivation to limit the fire, for example ammo supply that needs time to reload (so you can fire 5 projectiles, but then have to wait some time), or health that regenerates while you're not firing.
Interesting, i've been thinking about dropping bonuses and ammo crates at a random pace, however it complicates the game's balance.
I agree that 8 directions limit the gameplay, as you cannot really aim.
I guess i will have to implement mouse+keyboard control and analogic joypad too.
The smoke could be focused in front of the tank.
I'll make some tests as it shouldn't take long.
It would be nice to restart directly after game over.
Yeah, i have to add a menu in any case, with a start button and replay button, it should be a nice addition to my little engine as i need to implement a sort of scenes stack (
lifo) before i do the gui, there's some work to do in that area and i don't know if i'll be able to do it.
By the way, you should rather use unique_ptr instead of shared_ptr, unless you have a good reason for the latter 
You are right, i was not aware of unique_ptr existence. After a short analysis, it needs to be used with temporary entities as i call them in my engine because the main rendering class is the only one to own those entities (from instantiation to destruction).
I must say that i am a bit disappointed about the documentation i found about smart pointers (and c++ in general) on the internet, i do not mean reference websites as i mostly don't care about methods listing and short examples, i'm talking about good, complete, clear and fresh litterature on those cutting edges subjects.
(My highscore was 32)
Congratulations, most of my friends do an average of 30 points.
