Version: 2021.1
Asynchronous shader compilation
Shader variant collections

Shader loading

By default, Unity’s runtime shader 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 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 profiler marker for Unity creating a representation of shader variant data to send to the GPU is Shader.Parse. The profiler marker 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.

Asynchronous shader compilation
Shader variant collections