Detecting Collisions Once Per Object

[PushTheLimit]

Ok, so the game I'm working on is of the tower defense genre. I have turrets that are shooting mortars at the line of enemies. Once the mortars hit the map, an explosion animation plays and the enemies can take damage by passing over the animation. I'm checking against collision between the enemies and the mortar explosion animation to subtract damage from the health of the enemies. However, I don't want the damage to apply more than once to the same enemy when it passes over the explosion animation. I tried using "Only one action when event loops" limit condition to stop the health subtraction from happening every tick of game loop, however, when I have multiple explosion animation happening and two DIFFERENT enemies passing over the SEPARATE explosion animations, NO health is subtracted from EITHER enemy. Does anyone know of a solution to help tackle this problem? Do I need to keep track of whether a particular enemy already passed over a specific explosion and limit the action that way, or is there a simpler way? Also, the explosion animation plays for a long duration, such that multiple enemies can pass over the same explosion and each take damage, so it's not as simple as stopping/destroying the animation as soon as an enemy passes over it.

Thanks!

[BigHatLogan]

Are you testing for collision or overlap? Testing for collision should do it the way you want.

[PushTheLimit]

I tried it both ways to be sure, neither seemed to do the trick.

*Always
+Collision between Mortar and Enemy

will make it so it triggers the damage on every step of the game loop, and imperceptibly the enemy is destroyed immediately (even though it is really like 3 game ticks)

When I change to:

*Always
+Only one action when event loops
+Collision between Mortar and Enemy

It looks like it works at first, but when there are two different mortar animations occurring at the same time, and 2 different enemies simultaneously pass through their respective mortar explosions, they act like mutually exclusive locks and block either from registering damage.

[BigHatLogan]

Remove the "Always" from conditions. It's unnecessary.

[PushTheLimit]

Not to get off topic, does it add execution cycles to the runtime?

[RedRookLord]

Check if the explosion's animation frame is between 1 and 2. This will make first impact deal damage only.

[ProdigyX]

Any red event SHOULD be on top.

Collision Events are red.

Therefore any collision event should be on top.

[Danny]

Not to get off topic, does it add execution cycles to the runtime?

Depends, but in this instance, red events are immediate events so the runtime 'looks out' for these kind of red events (ie: collision detection/fastloops) and it will execute them as a priority over normal conditions... in your example there is no need for 'always' as the collision event will trigger the very split second it happens...

[gkinfinity]

Check if the explosion's animation frame is between 1 and 2. This will make first impact deal damage only.

This will only work if if it's overlapping the explosion during it's 1st or 2nd frame though. What if the explosion animation size starts off small and grows (as many explosion animations probably would)? An object that overlaps the explosion on frame 3 wouldn't detect the collision at all

[Spike]

Do
+ Explosion is overlapping Enemy (not colliding, overlapping)
+ Enemy Internal Flag 0 is off (or whatever flag you like)
- Set enemy Flag 0 on
- Take Damage

then a second event

+ NEGATE Explosion is overlapping enemy
- Set enemy flag 0 off

Should work I think