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Unity

Jan 06, 2025, 4 min read

Miscellaneous

  • Unity now supports object pooling out of the box using ObjectPool<T>. This allows for a stack based object pooling system.
  • Use ScriptableObject for objects that are not in the scene (i.e., they are not required to be game objects). Otherwise use Prefabs. See more here

Meshes

  • Mesh Filter - stores information about the mesh itself.
  • Mesh Renderer - responsible for rendering the mesh itself.
  • All triangles in Unity are drawn in a clockwise manner.

Compute Shaders

  • Compute Shaders work with either RenderTextures or StructuredBuffers.
  • Data is transferred from the CPU to the GPU via setting buffers, uniforms or textures.
  • The general flow for using Compute Shaders in Unity seems to be as follows:
    • Initialize any relevant data that is to be processed by the GPU.
      • Construct any textures as RenderTextures. We may blip from a Texture2D object to a RenderTexture object as needed.
      • Construct any structured buffers for other data that needs to be sent to the shader.
    • Pass all relevant data to the compute shader. (i.e., via Setter methods on the shader object itself)
    • Dispatch the compute shader to signal to the GPU that it should run.
    • Use any outputted textures from the GPU in the program.
  • Prefer the use of structures. It makes it easier to map to Structured Buffers.
  • Prefer the use of buffers when there is a need for precision.
  • Prefer outputting textures for grid-based data.
    • Keep in mind indexing operations require casting to int2.

DOTS

Use Cases

  • The game contains a lot of dynamic entities

  • The game requires complex algorithms such as Procedural Generation, pathfinding, dynamic AI, and heavy physics.

  • Competitive Multiplayer games that requires low latency and high accuracy

  • Large Scale Simulations

  • Running simulations in performance critical devices.

  • It is difficult to switch from MonoBehaviour to ECS. It is best to decide whether to use ECS early on in the project

Packages

  • Entity Component System - uses data oriented design to separate data from game logic which leads to modular, performant, and robust code.

    • Entities - corresponds to data components that represent one thing or part of a thing. Treated as part of a Database as it has a version number and index (for identifying which object it corresponds to).
    • Component - corresponds to the data associated with an entity stored in chunks which allows for fast access.
    • System - data transformations which modify values based on the gameplay. It runs on groups of entities with specified data components. It can be integrated with Jobs to allow for Multithreading

  • Entities Graphics - used for rendering entities in the game world.

  • Netcode for Entities - multiplayer networking compatible with ECS.

    • It allows for speed and accuracy when it comes to networked games
    • It is server authoritative so the simulation can run on the server.
    • Allows for client prediction to offset the latency caused by transferring data from client to server.
    • Simulated Rollbacks allow for undoing the simulation when there is a discrepancy between client side and server side.
    • Allows for high multiplayer counts.

  • DOTS Physics - free package for Physics

    • Stateless physics system.
    • No OnCollisionEnter or OnCollisionExit
    • Optimized for multiplayer (i.e., allows for simulated rollback)
    • Has built-in spatial querying to find entities in an area.

  • Havok Physics - paid package for Physics. Interchangeable with DOTS Physics. It is stateful but highly accurate.

  • Job System - allows for Multithreading in Unity

    • Automates scheduling and includes safety checks to avoid multithreading issues (i.e., deadlock and race conditions)
    • Allows for the benefits of multithreading and parallelization in Unity.
    • It is intended for work that needs to be completed within the same frame.
    • It can only be used on unmanaged data types.
    • It can be burst compiled.
    • Compatible with both ECS and MonoBehaviour.

  • Collections - a list of unmanaged Data Structures

    • Has some garbage collection capabilities but still requires memory management.
    • Has built-in safety checks (though there are unsafe variants that do not have these checks)

  • Burst Compiler - compiles code into native CPU code. It supports SIMD code.

  • Mathematics - includes burst compatible types.

Using DOTS

  • Components should only contain data not behaviors (see here).
  • You can add classes (refs) to the Component to be passed to the System. See here
  • Locking rotation requires a different setup in ECS. See here.

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