Version: 2021.1
Shader variant collections
Replacing shaders at runtime

Shader loading

By default, Unity’s runtime shaderA program that runs on the GPU. More info
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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
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    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 are first needed. This is called prewarming.

Warning: Check the notes on graphics API support before choosing how to perform prewarming. On modern graphics APIs such as DX12, Vulkan, and Metal, only the experimental ShaderWarmup API is fully supported, because it lets you specify a vertex format. Using the other methods can result in wasted work and GPU memory, without fixing the stalls.

You can perform prewarming in the following ways:


  1. Fully supported on all graphics APIs.
  2. Fully supported on DX11 and OpenGL. Partially supported on DX12, Vulkan, and Metal; the graphics driver might still need to perform work if the vertex layout and/or the render target setup is different from the data used to prewarm it.

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
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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
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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