Oldest Path of Exile Screenshot

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zeto wrote:

I'm curious if you have any additional resources that I might not have seen yet. I program entirely as a hobby, as I'm a lab rat during the week, so it's sorta difficult to find good write-ups and examples of such things when you aren't in the field.

The most complicated issues in architecture seem to be threading optimizations, inter-component or system communication special cases, and queue optimizations (most examples I've seen just iterate every entity/component without regard for need)

I don't have any specific resources to recommend at hand, but I have seen a ton of articles over the years. A bit of googling should find a lot of articles on the topic.

For iterating over components, we have two lists for each component type. One for "sleeping" components and one for "awake", but currently this is only performed on a per entity level.

As the players move around the level we increment / decrement a counter on each tile that represents the number of nearby player characters. When the counter goes to zero, the entity is slept and all the components move to the sleeping lists. This keeps the total number of things we need to iterate over reasonably low.

I'm planning at some point on allowing the components to sleep / wake up independently, but due to the relatively small number of entities that are in all of the players views at any one time (hundreds, not thousands), it hasn't really been an issue so far. Still, each bit of performance we can eek out of our servers means more players per server, which drives our server costs per user down.

In terms of threading, we don't have any general system for it at the component level. The reason for this is different depending on if you are looking at our clients, or servers.

On the server, we don't do any threading at all. This is because each instance server is it's own process. We can run hundreds of instances on each server so threading buys us absolutely nothing because the parallelism is already taken care of.

On the client, we could use threads at this level but I don't know how much of a win it would be. There are already several specific systems that can run in independent threads and take a fair amount of time in the frame (animation, particles, path-finding).

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zeto wrote:

Instancing and the ability to split and combine instances is probably one of the most powerful things to come out of "recent" gaming development, so I'm very interested to see how it goes here. I know that some sticking points with other projects have been smooth communication across their 'cluster controllers' to allow inter-instance communication; however that may not even be a consideration for POE as the game style is much different.

Communication between servers in the backend is certainly a big topic for PoE. It's funny because you end up implementing something that looks a lot like the internet. Our internal network has "routers" and hosts with addresses that have a network/host split.

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zeto wrote:

Anyway thank you for the conversation :) I really enjoy the technical aspects of design and execution as well as algorithms. The mere fact that the lead programmer and higher-ups actually use a forum at all to talk to the community is astonishing to me. Usually you get some sort of robotic pion PR guy who reads standard responses out of a book. :P

Thats fine. I enjoy discussing our techniques and I'm always interested in learning new things from other developers, so feel free to ask any questions you have about the technology we use and I'll answer them so long as it is not specifically about a feature we haven't announced yet.