ScriptableRenderContext.BeginScopedRenderPass

参数

描述

安排新渲染通道的开始。如果您在 using 语句中调用此方法，则 Unity 会在退出 using 块时自动调用 EndRenderPass。任何时候只能有一个渲染通道处于活动状态。

此方法与 BeginRenderPass 的作用相同，但它会返回一个 IDisposable，可以在 using 语句中使用，因此无需手动调用 EndRenderPass。

渲染通道提供了一种在可脚本化渲染管线上下文中切换渲染目标的新方法。与 SetRenderTargets 函数相反，渲染通道指定了渲染的明确开始和结束，以及对渲染表面的显式加载/存储操作。

渲染通道还允许在同一渲染通道内运行多个子通道，其中像素着色器可以读取渲染通道内当前像素值。这允许在基于平铺的 GPU（如延迟渲染）上有效地实现各种渲染方法。

渲染通道在 Metal（iOS）和 Vulkan 上以原生方式实现，但通过模拟（使用传统 SetRenderTargets 调用并通过纹素获取读取当前像素值），该 API 在所有渲染后端上都能完全发挥作用。

渲染通道机制具有以下限制：- 所有附件必须具有相同的分辨率和 MSAA 采样数 - 前一个子通道的渲染结果仅可通过着色器中的 UNITY_READ_FRAMEBUFFER_INPUT(x) 宏在同一屏幕空间像素坐标内获得；在渲染通道结束之前，无法将附件绑定为纹理或以其他方式访问 - iOS Metal 不允许从 Z 缓冲区读取，因此需要额外的渲染目标来解决此问题 - 每个渲染通道允许的最大附件数目前为 8 + 深度，但请注意，各种 GPU 可能有更严格的限制。

其他资源：BeginScopedSubPass。

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;
        using (context.BeginScopedRenderPass(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;
            using (context.BeginScopedSubPass(gbufferColors))
            {
                gbufferColors.Dispose();

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

            // 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;
            using (context.BeginScopedSubPass(lightingColors, lightingInputs, true))
            {
                lightingColors.Dispose();
                lightingInputs.Dispose();

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

            // 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;
            using (context.BeginScopedSubPass(tonemappingColors, tonemappingInputs, true))
            {
                tonemappingColors.Dispose();
                tonemappingInputs.Dispose();

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