Projectile client-side prediction
All moving projectiles in the game are normal entities tracked via the usual interpolated transform sync system. This is fine for AI characters shooting at you, but it's incredibly frustrating when you are shooting projectiles. You have to wait for a network round-trip before the projectile shows up.
I often test netcode on localhost, where there is no lag. Since this feature is heavily dependent on lag, I took some time during the stream this past Friday to implement a buffer that simulates network lag.
I cranked the lag up to 300ms total round-trip time and fired some projectiles. The first problem was that, since the server took 150ms to register my "fire projectile" command, my target might have moved by the time the projectile got to it.
The solution works like this on the server:
- Rewind the world 150ms to the point where the player fired
- Step forward in increments of 1/60th of a second until we reach the present, checking for obstacles along the way
- Spawn the projectile at the final position
- If a target was hit during this process, delete the projectile and apply any damage effects
To the player, there is still a 300ms delay before anything happens, but the projectile will pop into existence 20 feet out, where it would have been if there were no lag. This makes it easier to aim, but it's still annoying to have no immediate visual feedback when you fire.
I thought about spawning the projectile on the client. The problem is, projectiles are entities, and the entity system is controlled by the server. If I spawned projectiles on the client, IDs would get out of sync and things would explode.
So instead, I made a new system for fake projectiles, totally separate from the entities. Actually "system" is too strong a word, it's just an array of structs. These fake projectiles live for up to half a second, and the client removes them in order as soon as the server spawns a real projectile.
Here's the end result running with over 300ms of lag:
Shops
You can now buy stuff at these special locations known as "shops".
Locke has a number of greetings he can give, which will have accompanying animations. I'm really starting to enjoy animation work! Actually had a blast making this:
Also, this thing is now over 50,000 lines of code