Quote Originally Posted by Fursphere
I'm more confused now than I was before.
Let me try and clarify - Casting a shadowbolt normally takes 3 seconds (untalented). Currently, becuase the checking of whether you can cast spells or not is only done at the client side, you can effectively shave about 1/2 a second off your spell casting time using the /stopcasting command in a macro.
When the cast bar gets about 5/6 the way to the end, you can hit your macro button to cast another shadowbolt. The client side recognises the /stopcasting command, so stops casting, sends the request to the server, and starts casting the 2nd shadowbolt. But by the time the server receives the /stopcasting command, the spell is already completed, so it's ignored. But by this time the client side is already into the 2nd shadowbolt. The only catch with this is if you do it to early, you actually do stop casting your spell, so it's all in the timing...

With the new method, the checking on spell casting moves to the server side, so you don't need to use the /stopcasting command anymore. The problem is now however, clicking the macro button again for the 2nd shadowbolt triggers the GCD first, then checks with the server if it's ok to cast the spell. If its ok, all good and the spell casts, GCD continues at it's supposed to. If you hit the button too early though, the GCD still triggers, it checks with the server, the server denies the spell, and sends back the denial along with a request to cancel the GCD. Now, once the GCD is triggered, all other spells that use a GCD are locked out until either the GCD finsishes, or the client receives confirmation from the server that the GCD was not justified. For players in the US, the low latency (200 ms?) means that this doesn't affect them too much (although they are still worse off), since the request to cancel the GCD will come back from the server much faster (< 0.5 sec). But for customers not in the US (400 ms) it will probably be around just under a second before the the client recevies the request to cancel the GCD.

So in a nutshell, we have gone from situation where at worst a spell cast was cancelled if you hit a button too early, to a situation where all your spells could be locked out for close to one second depending on what your latency is. This has the biggest effect in raids (where you are trying to maximise your dps by getting off as many spells as possible over a certain time frame) and pvp (where triggering a GCD without casting a spell can be a death sentence).

Hope this helps...

Cheers,
Stealthy