The Tech Behind Swarm – Riot Video games Tech Weblog

Data-Driven Waves

We’re now capable of spawn a lot of minions that may goal and observe Champions everywhere in the map. The subsequent problem was the best way to give designers flexibility to creator all of the totally different waves whereas sustaining efficiency.

The League of Legends Engine has a C++ layer and a scripting layer. C++ is used to implement core gameplay and options that require a excessive diploma of effectivity (e.g., pathfinding), whereas script is used for extra high-level gameplay that requires quick iteration and suppleness (e.g., a selected spell).

Given the excessive turnover fee of minions in Swarm and all of the calculations and processing concerned in spawning and despawning each, we needed wave spawning to be as environment friendly as potential. To that finish, we created data-driven waves which might be dealt with in C++ and authored via information in editor, somewhat than script.

In information, designers management when waves spawn or despawn, which characters are in every wave, what number of minions are spawned, at what frequency, the place, and in what form… the checklist goes on! Most of those variables will be scaled by variety of gamers and problem degree.

Buff Batching

At this level, we have now waves of primordians which might be spawned based on wave information. Champions can assault these easy code-driven minions, however they can’t apply customized results on them, reminiscent of AoE stuns and harm over time.

All of those results are usually utilized via scripts known as “buffs.” These buffs are the first instruments designers use to implement gameplay mechanics. Unfortunately, buffs have been additionally the only most performance-draining side of the early prototype, presenting a notable scaling problem. So, what can we do when a repetitive activity begins to pressure efficiency? Enter batching!

The idea of buff batching is simple: somewhat than making use of a buff to every particular person minion, the buff is utilized to a bunch of minions concurrently. By batching the buff, we considerably cut back the overhead related to creating, sustaining, and destroying numerous buff cases for every affected minion. The relationship between minions and batches is many to many, the place every minion generally is a member of a number of batches, and every batch accommodates a number of minions. Each batch is represented by a set of reusable proxies, every carrying the buff related to the batch.

The main use case for batch buffs is making use of champion talents and weapon results onto a bunch of minions. For occasion, contemplate a capability like Leona’s ult, the place a single buff applies a timed AoE stun and harm over time to a number of targets.

Another use case is controlling the minions themselves. As I discussed earlier, most minions in Swarm can not carry buffs, besides bosses and mini-bosses. But what about these in-between instances, like elite minions, the place we have to spawn a lot of them, preserve the wave performant, however with a bit of additional aptitude? In these instances, a batch buff is added to the wave information as an elective habits, permitting designers extra management over these minions whereas nonetheless conserving buffs in examine.

I imagine that is the primary time in League historical past that we’ve had buffless minions that can not be immediately managed via script. Modifying the best way the sport has at all times been scripted was nerve-wracking, however I’ve to present it to the Swarm designers who rapidly adopted this fashion of scripting and nonetheless produced gameplay that feels genuine to League!

Client Optimization

Even after all of the optimizations we talked about, the sport nonetheless didn’t really feel performant. This was largely a shopper drawback, as a result of loopy quantity of issues on display screen abruptly. Despite our server capability metrics being inside goal, there have been nonetheless moments after we have been frightened that we must in the reduction of on the enjoyable to make the sport playable.