147 lines
7.0 KiB
Markdown
147 lines
7.0 KiB
Markdown
---
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uid: urp-render-graph-get-previous-frames
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---
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# Get data from previous frames
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To fetch the previous frames that the camera rendered in the Universal Render Pipeline (URP), use the [`UniversalCameraData.historyManager`](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@17.0/api/UnityEngine.Rendering.Universal.UniversalCameraData.html) API. These textures are sometimes called history textures or history buffers.
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The frames are the output of the GPU rendering pipeline, so they don't include any processing that occurs after GPU rendering, such as post-processing effects.
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To fetch previous frames from outside a scriptable render pass, refer to [Get data from previous frames in a script](#get-data-from-previous-frames-in-a-script).
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Follow these steps:
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1. In the `RecordRenderGraph` method, get the `UniversalCameraData` object from the `ContextContainer` object. For example:
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```csharp
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public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer frameContext)
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{
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UniversalCameraData cameraData = frameContext.Get<UniversalCameraData>();
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}
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```
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2. To request access to either the color textures or the depth textures in the rendering history, use the `RequestAccess` API. For example:
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```csharp
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// Request access to the color textures
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cameraData.historyManager.RequestAccess<RawColorHistory>();
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```
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Use `RawDepthHistory` instead to request access to the depth textures.
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3. Get one of the previous textures. For example:
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```csharp
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// Get the previous textures
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RawColorHistory history = cameraData.historyManager.GetHistoryForRead<RawColorHistory>();
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// Get the first texture, which the camera rendered in the previous frame
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RTHandle historyTexture = history?.GetPreviousTexture(0);
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```
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4. Convert the texture into a handle the render graph system can use. For example:
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```csharp
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passData.historyTexture = renderGraph.ImportTexture(historyTexture);
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```
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You can then read the texture in the render pass.
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For more information about using the `historyManager` API, refer to [`UniversalCameraData.historyManager`](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@17.0/api/UnityEngine.Rendering.Universal.UniversalCameraData.html).
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## Example
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The following is a Scriptable Renderer Feature that creates a material and uses the previous frame as the material's texture.
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To use the example, follow these steps:
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1. Create a URP shader that samples a texture called `_BaseMap`. For an example, refer to [Drawing a texture](writing-shaders-urp-unlit-texture.html).
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2. Create a material from the shader.
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3. Create a new C# script called `RenderLastFrameInMaterial.cs`, paste the following code into it, and save the file.
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4. In the active URP renderer, [add the Scriptable Renderer Feature](urp-renderer-feature-how-to-add.md).
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5. In the **Inspector** window of the active URP renderer, in the **Render Last Frame In Material** section of the Scriptable Renderer Feature you added in step 4, assign the material you created in step 2 to the **Object Material** field.
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```csharp
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using UnityEngine;
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using UnityEngine.Rendering;
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using UnityEngine.Rendering.Universal;
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using UnityEngine.Rendering.RenderGraphModule;
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public class RenderLastFrameInMaterial : ScriptableRendererFeature
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{
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public Material objectMaterial;
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CustomRenderPass renderLastFrame;
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public override void Create()
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{
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renderLastFrame = new CustomRenderPass();
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renderLastFrame.renderPassEvent = RenderPassEvent.BeforeRenderingOpaques;
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}
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public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
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{
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renderLastFrame.passMaterial = objectMaterial;
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renderer.EnqueuePass(renderLastFrame);
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}
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class CustomRenderPass : ScriptableRenderPass
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{
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public Material passMaterial;
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public class PassData
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{
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internal Material material;
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internal TextureHandle historyTexture;
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}
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public override void RecordRenderGraph(RenderGraph renderGraph, ContextContainer contextData)
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{
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UniversalCameraData cameraData = contextData.Get<UniversalCameraData>();
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// Return if the history manager isn't available
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// For example, there are no history textures during the first frame
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if (cameraData.historyManager == null) { return; }
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// Request access to the color and depth textures
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cameraData.historyManager.RequestAccess<RawColorHistory>();
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using (var builder = renderGraph.AddRasterRenderPass<PassData>("Get last frame", out var passData))
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{
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UniversalResourceData resourceData = contextData.Get<UniversalResourceData>();
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// Set the render graph to render to the active color texture
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builder.SetRenderAttachment(resourceData.activeColorTexture, 0, AccessFlags.Write);
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// Add the material to the pass data
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passData.material = passMaterial;
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// Get the color texture the camera rendered to in the previous frame
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RawColorHistory history = cameraData.historyManager.GetHistoryForRead<RawColorHistory>();
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RTHandle historyTexture = history?.GetPreviousTexture(0);
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passData.historyTexture = renderGraph.ImportTexture(historyTexture);
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builder.SetRenderFunc(static (PassData data, RasterGraphContext context) =>
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{
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// Set the material to use the texture
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data.material.SetTexture("_BaseMap", data.historyTexture);
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});
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}
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}
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}
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}
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```
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## Get data from previous frames in a script
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To get data from previous frames in a script, for example a `MonoBehaviour`, do the following:
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1. Use the Scriptable Render Pipeline (SRP) Core [`RequestAccess`](https://docs.unity3d.com/Packages/com.unity.render-pipelines.core@17.0/api/UnityEngine.Rendering.IPerFrameHistoryAccessTracker.html#UnityEngine_Rendering_IPerFrameHistoryAccessTracker_RequestAccess__1) API to request the texture.
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2. Use the [`UniversalAdditionalCameraData.history`](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@17.0/api/UnityEngine.Rendering.Universal.UniversalAdditionalCameraData.html#UnityEngine_Rendering_Universal_UniversalAdditionalCameraData_history) API to get the data.
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To make sure Unity finishes rendering the frame first, use the `UniversalAdditionalCameraData.history` API in the [`LateUpdate`](https://docs.unity3d.com/ScriptReference/MonoBehaviour.LateUpdate.html) method.
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For more information, refer to the following in the Scriptable Render Pipeline (SRP) Core package:
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- [`ICameraHistoryReadAccess`](https://docs.unity3d.com/Packages/com.unity.render-pipelines.core@17.0/api/UnityEngine.Rendering.ICameraHistoryReadAccess.html)
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- [`IPerFrameHistoryTracker`](https://docs.unity3d.com/Packages/com.unity.render-pipelines.core@17.0/api/UnityEngine.Rendering.IPerFrameHistoryAccessTracker.html)
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