Version: 2020.3
Shader variant collections
Replacing shaders at runtime

Shader loading

By default, Unity’s runtime shaderA program that runs on the GPU. More info
See in Glossary
loading behavior is:

  1. When Unity loads a scene, or loads content using runtime resource loading, it loads all required Shader objects into CPU memory.
  2. The first time Unity needs to render geometry using a shader variant, it passes the data for that variant to the graphics driver. The graphics driver creates a representation of that variant on the GPU, and performs any additional work that the platform requires.

The benefit of this behavior is that there is no upfront GPU memory usage or load time for shader variants. The downside is that there can be visible stalls when a variant is used for the first time, because the graphics driver must create the shader program on the GPU and perform any additional work.

Prewarming shader variants

To avoid visible stalls at performance-intensive times, Unity can ask the graphics driver to create GPU representations of shader variants before they’re first needed. This is called prewarming.

You can prewarm in the following ways:

You can also add shader variant collections to the Preloaded shaders section of the Graphics Settings window. Unity uses the ShaderVariantCollection.WarmUp API to load and prewarm the shader variant collections when your built application starts.

Prewarm on DirectX 12, Metal or Vulkan

If you build for DirectX 12, Metal or Vulkan, the graphics driver can only create an accurate GPU representation of a shader variant if it knows the exact vertex data layout and render state. If a prewarmed GPU representation is inaccurate, Unity might still stall when it needs to create the accurate representation.

To create accurate variants and avoid stalling, you should prewarm by renderingThe process of drawing graphics to the screen (or to a render texture). By default, the main camera in Unity renders its view to the screen. More info
See in Glossary
Materials off-screen.

You can also:

  • Prewarm a Shader object or shader variant collection using Experimental.Rendering.ShaderWarmup, but only if you can provide the vertex data layout and set the render state accurately.
  • Use ShaderVariantCollection.Warmup or Shader.WarmupAllShaders, which may create inaccurate prewarmed GPU representations because you can’t provide a vertex data layout or render state.

Profiler markers for shader loading

The profilerA window that helps you to optimize your game. It shows how much time is spent in the various areas of your game. For example, it can report the percentage of time spent rendering, animating, or in your game logic. More info
See in Glossary
marker for Unity creating a representation of shader variant data to send to the GPU is Shader.Parse. The profiler markerPlaced in code to describe a CPU or GPU event that is then displayed in the Unity Profiler window. Added to Unity code by default, or you can use ProfilerMarker API to add your own custom markers. More info
See in Glossary
for uploading the shader program to the GPU, and waiting for the GPU to perform any required work, is CreateGPUProgram.

For information on using the Unity Profiler, see Profile your application.

Shader variant collections
Replacing shaders at runtime