I want to make two sprites to gradually appear after that a group of sprites are destroyed.

To Tomycase:

Yes, the sprites are destroyed, when their instance variable is equal or inferior to zero they are destroyed (you can't see that in the piece of code displayed in my post but it is programmed somewhere else in my event sheet). What I want to do is this: When their instance variable is equal or inferior to zero and the sprites are all destroyed, the sub-event is supposed to be executed.

Well that's the problem, if the instances are destroyed, the program can't check their variables anymore as they're destroyed with the sprites, you would need to turn them invisible instead, but that can become a bit fastidious;

There are better methods that relay only on triggers instead of loops, give me some time and I'll prepare an example for you ~

EDIT : before I prepare the example, do you know about loopidex and how to use it?

To Tomycase:

No, I never heard or saw anything named "loopidex" before. What is this? What does it do? what is the purpose of that thing?

Thank you in advance for the example!

Perfect! Here is the example then :

This is the result I get : i.ibb.co/h7MFhfn/Example.gif

3 enemies, I destroy them and the face appears gradually with the forcefield;

This is how I achieved it :

What I did, is to put all the enemies in a common family, and give a variable named "Activation" to the computer face sprite;

When a sprite from the enemy family is destroyed, it adds 1 to "Activation"; When this variable reachs the number of enemy you want, it triggers that event once :

"Wait 1 second > Repeat 4 times : Wait loopindex*(time you want) > opacity+25

Loopindex represents the index of the current loop, in this event when it repeats 4 times, the first loop index = 0, second loop = 1, third loop = 2; etc (index always starts from 0 unless you use a "For" loop)

The 4 loops trigger at the same time, but the wait action delay is equal to the loop index multiplied by the number of your choice, which means in the example that the first opacity adjustement triggers at 0*0.5 = 0s, second at 1*0.5 = 0.5s, third at 2*0.5 = 1s, etc;

That way you have events that rely only on triggers instead of a loops with the result you wanted ^^

Be careful however if you use that loopindex method to not use it into a looping condition, otherwise it will repeat constantly, it needs to be triggered a single time (with a trigger event or "trigger once while true);

Btw unrelated but I guess your turrets and cannons works the same right? Because I see that you create two differents objects for each, meaning that you had to duplicate the code for each, when you could diplucate them on layout then mirror the sprites and use a single code, it would simplify things a lot; if you don't know how to do I can help on that too ~

To Tomycase:

Yes, you were right! I am having problems. The game seems to have a bug because I have too much code. Explain to me how to duplicate the sprites on the layout then mirror the sprites and use a single code, to save memory. I thought that it was not very important but now it's causing issues.

Thank you!

To Tomycase:

Maybe by showing how I have organized the code for the Turrets and the laser cannon, you will be able to tell me what I should delete and conserve to save memory:

(Note that the Sine Behaviour was applied for the Horizontal Cannon that the reason why there is no code concerning their movement):