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Unity ECS On Quest 2

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At Red Team Interactive, we've been considering using Unity 6's Entity Component System (ECS) for mobile VR. It boasts incredible performance on both the CPU and the GPU with many entities, even in a multiplayer game. As all of the games we make are multiplayer, we love the idea of being able to create larger, more immersive worlds for more and more individuals.

We did a foray into the system to see how much of a performance gain it would give us. In our test, there are 3 situations, each with an ECS implementation and an Game Object System (GOS) implementation. The 3 questions that we wanted answered by the situations were:

• How many animated skinned mesh entities could each system handle? (low simulation, high rendering)
• How many boids (in a classical 3D boid simulation) could each system handle? (high simulation, low rendering)
• How many simple-logic dynamic objects could each system handle? (low simulation, low rendering)

⚠️ Disclaimer ⚠️

I made this project as I was learning about ECS, Unity Jobs, and shaders. There are improvements that can be made to each of the tests. Regardless, I believe that these tests indicate the great potential that ECS has for mobile VR.

Test Setup

Each test is done on-device with a Quest 2 and a Quest 3. Each GOS implementation uses jobs to manage all of the objects. During each test, the number of entities or objects were increased until the average FPS dropped below 72 on either the Quest 2 or Quest 3. ECS greatly outperformed GOS by 2-30x. All images/gifs of these tests are ECS implementations.

Test 1 - Animated Skinned Mesh Entities

This test was born from our idea about a 3D shoot 'em up, bullet hell, extraction zombie shooter in VR: Z-Route. The idea is that players would go out into a post-apocalyptic environment where zombies run wild. The players would drive a weaponized school bus to their mission objective, complete the objective, and then return to base. Our hope is that there would be masses of zombies that the players could mow down, explode, or destroy in whichever way they fancy.

The test involves spawning as many animated zombies as possible within an area. Both the ECS and the GOS have a similar setup: spawn zombies that move forward in circles. The ECS version utilizes an free GPU-based ECS animator asset from the Unity Asset Store. The GOS implementation uses the built-in animator as well as jobs to move the zombies.

Test Results

The ECS implementation outperformed the GOS implementation by about 2x on the Quest 2 and about 3x on the Quest 3.

• Quest 2 ECS: 1k entities
• Quest 3 ECS: 1.7k objects
• Quest 2 GOS: 650 entities (CPU bound)
• Quest 3 GOS: 650 objects (CPU bound)

It's interesting to me that the GOS implementation struggled at the CPU mark. It makes me think that there is still room to improve for the GOS implementation. I'm not 100% confident about my abilities to use Unity Jobs.

Test 2 - Boid Simulation

ECS really outshone GOS in this test. This is a conventional boids algorithm implementation confined within a 3D cube. The cube is broken up into a spatial hash-map. Each boid must know its neighbors' states (direction and position) and modify its own in accordance. I'd like to point out that I'm not 100% confident in my Unity Jobs implementation. Regardless, I think that this particular test highlights ECS's ability to multithread logic very efficiently. This allows it to handle massive amounts of entities.

Test Results

ECS outperformed GOS by 15-30x 🔥

• Quest 2 ECS: 15k entities
• Quest 3 ECS: 30k objects
• Quest 2 GOS: 950 entities
• Quest 3 GOS: 1k objects

Test 3 - Simple-Logic Objects

This test showed how each system could handle rendering thousands of "simple" objects. Each object bobbed up & down in a simple sine wave. The entities/objects were arrayed in such a way that all of them could be seen within the camera's view frustrum.

Test Results

ECS outperformed GOS by 5-6x.

• Quest 2 ECS: 20k entities
• Quest 3 ECS: 30k objects
• Quest 2 GOS: 3k entities
• Quest 3 GOS: 6.5k objects

This test illustrates how efficient the ECS Entities Graphics package is.