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 objectsAn instance of the Shader class, a Shader object is container for shader programs and GPU instructions, and information that tells Unity how to use them. Use them with materials to determine the appearance of your scene. More info
   See in Glossary 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:

• Prewarm a Shader object or shader variant collection using the Experimental.Rendering.ShaderWarmup API.
• Prewarm a shader variant collection by using the ShaderVariantCollection.WarmUp API.
• Prewarm all variants of all Shader objects currently in memory using the Shader.WarmupAllShaders API.

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 rendering 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.

Control how much memory shaders use

In your built application, Unity stores several ‘chunks’ of compressed shader variant data. Each chunk contains multiple shader variants. When Unity loads a sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary at runtime, it loads all the scene’s chunks into CPU memory and decompresses them.

To reduce memory usage on platforms that have limited memory, you can limit the size of chunks and how many decompressed chunks Unity keeps in memory.

To do this, in Player settingsSettings that let you set various player-specific options for the final game built by Unity. More info
See in Glossary, select Other Settings > Shader Variant Loading and adjust the following settings:

• Use Default chunk size (MB) to set the maximum size of compressed chunks Unity stores in your built application.
• Use Default chunk count to limit how many decompressed chunks Unity keeps in memory. The default is 0, which means there’s no limit.

See PlayerSettings.SetDefaultShaderChunkCount for more information.

You can use Override to override the values for each platform individually. See PlayerSettings.SetShaderChunkCountForPlatform for more information.

You can also use Shader.maximumChunksOverride to override Default chunk count at runtime.

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.