Introduction to dynamic batching

Dynamic batching is a draw call batching method that batches moving GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary to reduce draw calls. It can improve performance, memory efficiency, and reduce CPU overhead, leading to a smoother frame rate and better player experience, especially in scenarios with many small objects or on lower-end devices.

Dynamic batching works differently between meshes and geometries that Unity generates dynamically at runtime, such as particle systemsA component that simulates fluid entities such as liquids, clouds and flames by generating and animating large numbers of small 2D images in the scene. More info
See in Glossary. For information about the internal differences between meshes and dynamic geometries, refer to Dynamic batching for meshes and Dynamic batching for dynamically generated geometries.

Note: Dynamic batchingAn automatic Unity process which attempts to render multiple meshes as if they were a single mesh for optimized graphics performance. The technique transforms all of the GameObject vertices on the CPU and groups many similar vertices together. More info
See in Glossary for meshes was designed to optimize performance on old low-end devices. On modern consumer hardware, the work dynamic batching does on the CPU can be greater than the overhead of a draw call. This negatively affects performance. For more information, refer to Dynamic batching for meshes.

How Unity batches moving GameObjects

Dynamic batching for meshes works by transforming all vertices into world space on the CPU, rather than on the GPU. This means dynamic batching is only an optimization if the transformation work is less resource-intensive than doing a draw call.

The resource requirements of a draw call depend on many factors, primarily the graphics API. For example, on consoles or modern APIs like Apple Metal, the draw call overhead is generally much lower, and often dynamic batching doesn’t produce a gain in performance. To determine whether it’s beneficial to use dynamic batching in your application, profile your application with and without dynamic batching.

Unity can use dynamic batching for shadow casters, even if their materials are different, as long as the material values Unity needs for the shadow pass are the same. For example, multiple crates can use materials with different textures. Although the material assets are different, the difference is irrelevant for the shadow caster pass, and Unity can batch shadows for the crate GameObjects in the shadow render step.

Requirements and compatibility

This section includes information about the render pipelineA series of operations that take the contents of a Scene, and displays them on a screen. Unity lets you choose from pre-built render pipelines, or write your own. More info
See in Glossary compatibility of dynamic batching.

Render pipeline compatibility

Resource requirements

The resource requirements of a draw call depend on the graphics API. To determine if dynamic batching is beneficial in your application, profile your application with and without dynamic batching enabled.

Dynamic batching for meshes

Dynamic batching for meshes transforms all vertices into world space on the CPU rather than on the GPU. This only optimizes performance if the transformation work is less resource-intensive than doing a draw call.

Shadow casters

Unity can use dynamic batching for shadow casters even if their materials differ, as long as the material values required for the shadow pass are the same. For example, multiple crates can use different textures, but Unity can batch shadows for the crate GameObjects in the shadow render step.

Limitations

In the following scenarios, Unity either can’t use dynamic batching at all or can only apply dynamic batching to a limited extent:

• Unity can’t apply dynamic batching to meshes that contain more than 900 vertex attributes and 300 vertices. This is because dynamic batching for meshes has an overhead per vertex. For example:

• If your shaderA program that runs on the GPU. More info
  See in Glossary uses vertex position, vertex normal, and a single UV, then Unity can batch up to 300 vertices.

• If your shader uses vertex position, vertex normal, UV0, UV1, and vertex tangent, then Unity can only batch 180 vertices.

• If GameObjects use different material instances, Unity can’t batch them together, even if they are essentially the same. The only exception to this is shadow caster rendering.

• GameObjects with lightmaps have additional renderer parameters. This means that, if you want to batch lightmapped GameObjects, they must point to the same lightmapA pre-rendered texture that contains the effects of light sources on static objects in the scene. Lightmaps are overlaid on top of scene geometry to create the effect of lighting. More info
  See in Glossary location.

• Unity can’t fully apply dynamic batching to GameObjects that use multi-pass shaders.
  • Almost all Unity shaders support several lights in forward renderingA rendering path that renders each object in one or more passes, depending on lights that affect the object. Lights themselves are also treated differently by Forward Rendering, depending on their settings and intensity. More info
    See in Glossary. To achieve this, they process an additional render pass for each light. Unity only batches the first render pass. It can’t batch the draw calls for the additional per-pixel lights.

Dynamic batching for dynamically generated geometries

Dynamic batching works differently for geometries that Unity generates dynamically, such as particles and lines. The following renderers generate geometries that can be optimized using dynamic batching:

• Built-in Particle Systems
• Line RenderersA component that takes an array of two or more points in 3D space and draws a straight line between each one. You can use a single Line Renderer component to draw anything from a simple straight line to a complex spiral. More info
  See in Glossary
• Trail RenderersA visual effect that lets you to make trails behind GameObjects in the Scene as they move. More info
  See in Glossary

Dynamic batching process for dynamically generated geometries

Dynamic batching for dynamically generated geometries works differently than it does for meshes:

1. Unity builds all dynamically batchable content into one large vertex buffer per renderer.
2. The renderer sets up the material state for the batch.
3. Unity binds the vertex buffer to the GPU.
4. For each renderer in the batch, Unity updates the offset in the vertex buffer and submits a new draw call.

This approach resembles how Unity submits draw calls for static batchingA technique Unity uses to draw GameObjects on the screen that combines static (non-moving) GameObjects into big Meshes, and renders them in a faster way. More info
See in Glossary.