[Gameplay] Movement ability(flash) + skillshot bug

So I've come across this bug a few times and I wrote down my thoughts on the reddit thread but I thought that I should probably share them here as well. I'll mostly just copy + paste what I wrote there, but the gist of the bug is that due to the nature of how networks operate, when skillshots are cast within a specific timing window after an instantaneous movement ability, the cast direction is calculated based upon the cursors relative location to the champion's previous location rather than the chamion's new location

(begin copy+paste)

This is a bug with casting immediately after an instantaneous movement ability(flash, teleport, etc.) Due to the fact that there is a slight delay between client side resolution of commands and server side, sometimes when you cast a skillshot immediately after a movement command, the direction part of the skillshot command resolves before the server has resolved the end of the movement command and sent the new location back to the client.

(side note: requires testing but this may not necessarily be related to instantaneous movement but rather movement that can be cast at larger than max range and then calculates the max distance in that location. In other words, the end location is calculated server side rather than client side which results in the delay, in which case teleport may no longer be a problem because it always resolves to one side now.)

If you look at his mouse location at the exact moment he casts his ult, you can see from the still remaining flash particles that it's the same angle from his flash location as Vel'koz ults from his new location.

Basically what happens is this:

1. Vel'koz casts flash
2. client computer sends command to server telling server to execute the movement command from current location 3)Server begins resolving new location 4)Immediately after sending the movement command Client computer sends command for spellcast(including cast location) based on its current location (here's * where the bug starts because the client hasn't updated its location yet)
3. Server resolves new location and sends data back to client, Also begins resolving cast of skillshot based on the cast location it received and the new champion location it has calculated
4. Client side, spell is cast from updated location in direction from previous location Proof(kinda): http://imgur.com/ubSH465 In this screenshot, the cast angle of vel'koz's ult is the same angle that his cursor is from vel'koz's previous location.

Also, after doing some more thinking, it's possible that there is a ping(ping being the amount of time it takes for a command to reach a server and come back) sweetspot for stuff like this to occur. I've personally noticed this happening a lot more ever since Riot moved their servers to Chicago and I kinda just naturally adjusted to delay a few frames when doing flash ults. Essentially, the sweetspot is probably somewhere between 20-50 ping. Where if you had less ping, the server would refresh your location client side in time for your ult occur properly, and if you had higher ping, the spell cast command would not reach the server in time for this bug to occur as the server already has the new location and will calculate the angle based on the new location.

As a side note, I wonder if movement prediction would help with this problem

Edit: fixed some wording based on the timing of what's happening