Version: 2020.1
public void BeginRenderPass (int width, int height, int samples, NativeArray<AttachmentDescriptor> attachments, int depthAttachmentIndex);

参数

width 渲染通道表面的宽度(以像素为单位)。
height 渲染通道表面的高度(以像素为单位)。
samples MSAA 样本数;设置为 1 以禁用抗锯齿。
attachments 渲染通道中使用的颜色附件数组。数组中的值会立即复制。
depthAttachmentIndex 用作此渲染通道的深度/模板缓冲区的附件索引,或为 -1 以禁用深度/模板。

描述

调度新渲染通道的开头。在任何时候只能有一个渲染通道处于活动状态。

渲染通道是一种在可编程渲染管线环境中切换渲染目标的全新方式。与 SetRenderTargets 函数不同,渲染通道指定了明确的渲染开头和结尾以及渲染表面上的显式加载/存储操作。

渲染通道还允许在同一渲染通道中运行多个子通道,其中,像素着色器能够读取渲染通道中的当前像素值。这样可以高效实现基于瓦片的 GPU 上的各种渲染方法,例如延迟渲染。

渲染通道在 Metal (iOS) 和 Vulkan 上原生实现,但 API 能够通过仿真在所有渲染后端上完全正常运行(使用旧版 SetRenderTargets 调用并通过纹素抓取读取当前像素值)。

渲染通道机制具有以下限制:
- 所有附件必须拥有相同的分辨率和 MSAA 样本数
- 先前子通道的渲染结果仅通过着色器中的 UNITY_READ_FRAMEBUFFER_INPUT(x) 宏
在相同的屏幕空间像素坐标中可用; 附件不能绑定为纹理或直到渲染通道结束才能访问
- iOS Metal 不允许从 Z 缓冲区读取,因此需要其他渲染目标来执行这项操作
- 每个渲染通道允许的最大附件数量目前是 8 + 深度,但请注意,不同的 GPU 可能 有更严格的限制。


另请参阅:BeginSubPassEndRenderPassBeginScopedRenderPassBeginScopedSubPass

一个有关如何在可编程渲染管线中使用渲染通道 API 实现延迟渲染的简单示例:

using UnityEngine;
using UnityEngine.Rendering;
using Unity.Collections;

public static class DeferredRenderer { public static void ExecuteRenderLoop(Camera camera, CullingResults cullResults, ScriptableRenderContext context) { // Create the attachment descriptors. If these attachments are not specifically bound to any RenderTexture using the ConfigureTarget calls, // these are treated as temporary surfaces that are discarded at the end of the renderpass var albedo = new AttachmentDescriptor(RenderTextureFormat.ARGB32); var specRough = new AttachmentDescriptor(RenderTextureFormat.ARGB32); var normal = new AttachmentDescriptor(RenderTextureFormat.ARGB2101010); var emission = new AttachmentDescriptor(RenderTextureFormat.ARGBHalf); var depth = new AttachmentDescriptor(RenderTextureFormat.Depth);

// At the beginning of the render pass, clear the emission buffer to all black, and the depth buffer to 1.0f emission.ConfigureClear(new Color(0.0f, 0.0f, 0.0f, 0.0f), 1.0f, 0); depth.ConfigureClear(new Color(), 1.0f, 0);

// Bind the albedo surface to the current camera target, so the final pass will render the Scene to the screen backbuffer // The second argument specifies whether the existing contents of the surface need to be loaded as the initial values; // in our case we do not need that because we'll be clearing the attachment anyway. This saves a lot of memory // bandwidth on tiled GPUs. // The third argument specifies whether the rendering results need to be written out to memory at the end of // the renderpass. We need this as we'll be generating the final image there. // We could do this in the constructor already, but the camera target may change on the fly, esp. in the editor albedo.ConfigureTarget(BuiltinRenderTextureType.CameraTarget, false, true);

// All other attachments are transient surfaces that are not stored anywhere. If the renderer allows, // those surfaces do not even have a memory allocated for the pixel values, saving RAM usage.

// Start the renderpass using the given scriptable rendercontext, resolution, samplecount, array of attachments that will be used within the renderpass and the depth surface var attachments = new NativeArray<AttachmentDescriptor>(5, Allocator.Temp); const int depthIndex = 0, albedoIndex = 1, specRoughIndex = 2, normalIndex = 3, emissionIndex = 4; attachments[depthIndex] = depth; attachments[albedoIndex] = albedo; attachments[specRoughIndex] = specRough; attachments[normalIndex] = normal; attachments[emissionIndex] = emission; context.BeginRenderPass(camera.pixelWidth, camera.pixelHeight, 1, attachments, depthIndex); attachments.Dispose();

// Start the first subpass, GBuffer creation: render to albedo, specRough, normal and emission, no need to read any input attachments var gbufferColors = new NativeArray<int>(4, Allocator.Temp); gbufferColors[0] = albedoIndex; gbufferColors[1] = specRoughIndex; gbufferColors[2] = normalIndex; gbufferColors[3] = emissionIndex; context.BeginSubPass(gbufferColors); gbufferColors.Dispose();

// Render the deferred G-Buffer // RenderGBuffer(cullResults, camera, context);

context.EndSubPass();

// Second subpass, lighting: Render to the emission buffer, read from albedo, specRough, normal and depth. // The last parameter indicates whether the depth buffer can be bound as read-only. // Note that some renderers (notably iOS Metal) won't allow reading from the depth buffer while it's bound as Z-buffer, // so those renderers should write the Z into an additional FP32 render target manually in the pixel shader and read from it instead var lightingColors = new NativeArray<int>(1, Allocator.Temp); lightingColors[0] = emissionIndex; var lightingInputs = new NativeArray<int>(4, Allocator.Temp); lightingInputs[0] = albedoIndex; lightingInputs[1] = specRoughIndex; lightingInputs[2] = normalIndex; lightingInputs[3] = depthIndex; context.BeginSubPass(lightingColors, lightingInputs, true); lightingColors.Dispose(); lightingInputs.Dispose();

// PushGlobalShadowParams(context); // RenderLighting(camera, cullResults, context);

context.EndSubPass();

// Third subpass, tonemapping: Render to albedo (which is bound to the camera target), read from emission. var tonemappingColors = new NativeArray<int>(1, Allocator.Temp); tonemappingColors[0] = albedoIndex; var tonemappingInputs = new NativeArray<int>(1, Allocator.Temp); tonemappingInputs[0] = emissionIndex; context.BeginSubPass(tonemappingColors, tonemappingInputs, true); tonemappingColors.Dispose(); tonemappingInputs.Dispose();

// present frame buffer. // FinalPass(context);

context.EndSubPass();

context.EndRenderPass(); } }