着色器加载

默认情况下，Unity 的运行时着色器加载行为如下：

1. 当 Unity 加载场景或使用在运行时加载资源功能加载内容时，它会将所有需要的 Shader 对象加载到 CPU 内存。
2. Unity 第一次需要使用着色器变体渲染几何体时，它将该变体的数据传递给图形驱动程序。图形驱动程序在 GPU 上创建该变体的表示，并执行平台所需的任何其他工作。

这种行为的好处是着色器变体没有前期的 GPU 内存使用或加载时间。缺点是第一次使用变体时可能会出现明显的停顿，因为图形驱动程序必须在 GPU 上创建着色器程序并执行任何额外的工作。

预热着色器变体

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.

还可以：

• 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 scene 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 settings, 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.

用于着色器加载的性能分析器标记

性能分析器标记 Shader.Parse 用于表示 Unity 将创建的着色器变量数据表示发送到 GPU。性能分析器标记 CreateGPUProgram 用于表示将着色器程序上传到 GPU 并等待 GPU 执行任何所需工作。

有关使用 Unity 性能分析器的信息，请参阅对应用程序进行性能分析。