there are about a million ways to do this
this is just one, and it does not use collisions/regions or anything fancy.
this particular version will ONLY trigger the "in vision" event for each actor once, ie: the FIRST time that particular actor comes on screen.
ie: once only for every actor as it first appears. actors/objects already on screen, will not trigger until they leave vision and then return
it can be easily changed to retrigger everytime any actors come and go off screen
in this example every "block" will explode as it comes on screen - try cloning more blocks for lotsa fun.. LOL
should be well commented... but, if does not make sense let me know
PS: BTW yeah I agree . it probably would still be a good idea to include the "into vision", as an event -
it would be easier..