Game Mechanics: Casting spells and attack speed

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Lets say your delay is 20, and you cast a spell that takes 3 seconds, as soon as you cast you will immediately swing because you missed your last attack.

This feature was not implemented til around velious, until that point your attack delay was set and only happened on the times of swings. if you casted and missed a swing you waited for the next swing, it did not immediately give you a swing after the cast.