本页介绍如何使用渲染图系统编写渲染通道。
为了举例说明，页面使用示例渲染通道将摄像机的活动颜色纹理复制到目标纹理。为了简化代码，此示例不使用帧中其他位置的目标纹理。您可以使用帧调试器检查其内容。
将渲染通道声明为继承自 ScriptableRenderPass 类的类。
在渲染通道中，声明一个包含渲染通道使用的资源的类。
资源可以是常规 C# 变量和渲染图资源引用。渲染图系统可以在渲染代码执行期间访问此数据结构。确保仅声明渲染通道使用的变量。添加不必要的变量可能会降低性能。
class PassData
{
internal TextureHandle copySourceTexture;
}
RecordRenderGraph 方法填充数据，渲染图将其作为参数传递给渲染函数。
声明一个渲染函数，用于为渲染通道生成渲染命令。在此示例中，RecordRenderGraph 方法进一步指示渲染图使用一个使用 SetRenderFunc 方法的函数。
static void ExecutePass(PassData data, RasterGraphContext context)
{
// Records a rendering command to copy, or blit, the contents of the source texture
// to the color render target of the render pass.
// The RecordRenderGraph method sets the destination texture as the render target
// with the UseTextureFragment method.
Blitter.BlitTexture(context.cmd, data.copySourceTexture,
new Vector4(1, 1, 0, 0), 0, false);
}
使用 RecordRenderGraph 方法可在渲染图系统中添加和配置一个或多个渲染通道。
Unity 在渲染图配置步骤中调用此方法，并允许您注册用于渲染图执行的相关通道和资源。使用此方法可实现自定义渲染。
在 RecordRenderGraph 方法中，可以声明渲染通道输入和输出，但不向命令缓冲区添加命令。
以下部分介绍 RecordRenderGraph 方法的主要内容并提供示例实现。
builder 变量是 IRasterRenderGraphBuilder 接口的实例。此变量是用于配置与渲染通道相关信息的入口点。
UniversalResourceData 类包含 URP 使用的所有纹理资源，包括摄像机的活动颜色和深度纹理。
UniversalCameraData 类包含与当前活动摄像机相关的数据。
出于演示目的，此示例创建一个临时目标纹理。UniversalRenderer.CreateRenderGraphTexture 是调用 RenderGraph.CreateTexture 方法的 helper 方法。
TextureHandle destination =
UniversalRenderer.CreateRenderGraphTexture(renderGraph, desc, "CopyTexture", false);
builder.UseTexture 方法声明此渲染通道使用源纹理作为只读输入：
builder.UseTexture(passData.copySourceTexture);
在此示例中，builder.SetRenderAttachment 方法声明此渲染通道使用临时目标纹理作为其颜色渲染目标。此声明类似于可在兼容性模式下使用的 cmd.SetRenderTarget API（不含渲染图 API）。
SetRenderFunc 方法将 ExecutePass 方法设置为执行渲染通道时渲染图形调用的渲染函数。此示例使用 lambda 表达式来避免内存分配。
builder.SetRenderFunc((PassData data, RasterGraphContext context) => ExecutePass(data, context));
RecordRenderGraph 方法的完整示例如下：
// This method adds and configures one or more render passes in the render graph.
// This process includes declaring their inputs and outputs,
// but does not include adding commands to command buffers.
public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer frameData)
{
string passName = "Copy To Debug Texture";
// Add a raster render pass to the render graph. The PassData type parameter determines
// the type of the passData output variable.
using (var builder = renderGraph.AddRasterRenderPass<PassData>(passName,
out var passData))
{
// UniversalResourceData contains all the texture references used by URP,
// including the active color and depth textures of the camera.
UniversalResourceData resourceData = frameData.Get<UniversalResourceData>();
// Populate passData with the data needed by the rendering function
// of the render pass.
// Use the camera's active color texture
// as the source texture for the copy operation.
passData.copySourceTexture = resourceData.activeColorTexture;
// Create a destination texture for the copy operation based on the settings,
// such as dimensions, of the textures that the camera uses.
// Set msaaSamples to 1 to get a non-multisampled destination texture.
// Set depthBufferBits to 0 to ensure that the CreateRenderGraphTexture method
// creates a color texture and not a depth texture.
UniversalCameraData cameraData = frameData.Get<UniversalCameraData>();
RenderTextureDescriptor desc = cameraData.cameraTargetDescriptor;
desc.msaaSamples = 1;
desc.depthBufferBits = 0;
// For demonstrative purposes, this sample creates a temporary destination texture.
// UniversalRenderer.CreateRenderGraphTexture is a helper method
// that calls the RenderGraph.CreateTexture method.
// Using a RenderTextureDescriptor instance instead of a TextureDesc instance
// simplifies your code.
TextureHandle destination =
UniversalRenderer.CreateRenderGraphTexture(renderGraph, desc,
"CopyTexture", false);
// Declare that this render pass uses the source texture as a read-only input.
builder.UseTexture(passData.copySourceTexture);
// Declare that this render pass uses the temporary destination texture
// as its color render target.
// This is similar to cmd.SetRenderTarget prior to the RenderGraph API.
builder.SetRenderAttachment(destination, 0);
// RenderGraph automatically determines that it can remove this render pass
// because its results, which are stored in the temporary destination texture,
// are not used by other passes.
// For demonstrative purposes, this sample turns off this behavior to make sure
// that render graph executes the render pass.
builder.AllowPassCulling(false);
// Set the ExecutePass method as the rendering function that render graph calls
// for the render pass.
// This sample uses a lambda expression to avoid memory allocations.
builder.SetRenderFunc((PassData data, RasterGraphContext context)
=> ExecutePass(data, context));
}
}
要将可编程渲染通道实例注入渲染器，请使用渲染器功能实现中的 AddRenderPasses 方法。URP 每帧都会调用 AddRenderPasses 方法，每个摄像机调用一次。
public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
{
renderer.EnqueuePass(m_CopyRenderPass);
}