making non-autocast spells autocast

I've seen this in burbenog TD.
in it, you can click an ability called autocast on and autocast off and it makes forked lightning autocast... how can I do something similar?

Unit enters within say 500 of caster, cast (insert spell here) on triggering unit...somthin like that...hope it helps, ill get code if u want.

Untitled Trigger 001
Events
Unit - A unit comes within 500.00 of <building> 0000 <gen>
Conditions
Actions
Unit - Order <building> 0000 <gen> to <spell here> (Triggering unit)

Nvm, Hiro got code for ya, THERE YA GO UR ALL SET!
THANK YOU COME AGAIN!
lol

no, that is not how its done.

Unit is attacked
attacking unit = to <your tower type here>
Order attacking unit to <Your spell here> at attacked unit.

....In burbenog they dont attack your towers silly....

hey dipshit, try reading what I wrote

it detects towers attacking units, not the other way around. Idiot

In burbenog the towers dont attack the unit then cast the spell, the spell towers dont even have a attack...silly...

omfg, you are truely an idiot

They have a spell attack that does 1-1 dmaage and has no projectile. Go look, I dare you.

I dont think thats what he wants. I thought he wanted it that a spell would atuocast itself whenever that unit can attack another unit. So making it so that an event is activated when that unit is attacking another unit to cast it on the unit that is being attacked wont work. THe "Comes within range" event will work better at least it does when i just tested it.

Hunter, ease up on the insults. This thread is for people who need help, not people who know everything; quit jumping down everyone's throat.

Ya what he said last thing we need is a flame war... *puts away flamethrowers*

Lol, hunters response was perfectly justifiable

On another note, is there a way to make this trigger enable/disable, like how you can right-click on spells that support autocasting inherently?

Wow that sounds an awfull lot like he wants it for a tower doesn't it?

Yes yes, you cannot tell me after looking at Vilkacis's posts that he was not trolling, witch if I might remind you is also agaist the rules.

EDIT: To make it turn-offable, make that trigger only work when they have a custom value of 0, now make a dummy skill that sets the custom value to 1(Off) and one that sets it to 0(On)