Single-Pass Stereo Rendering for HoloLens——HoloLens的单程立体渲染

原文网站：https://docs.unity3d.com/Manual/SinglePassStereoRenderingHoloLens.html

Single-Pass Stereo Rendering for HoloLens

HoloLens的单程立体渲染

There are two stereo rendering methods for Windows Holographic devices (HoloLens); multi-pass and single-pass instanced.

当前有两种针对windows全息设备（HoloLens）的立体渲染方法；多程渲染和单程渲染。

Multi-pass

Multi-pass rendering runs 2 complete render passes (one for each eye). This generates almost double the CPU workload compared to the single-pass instanced rendering method. However this method is the most backwards compatible and doesn’t require any shader changes.

多程渲染会完成两次完整的渲染过程（每只眼睛一次）。相比于单程渲染方法，这会导致将近两倍的 CPU工作量。然而这是向后兼容性最好的方法，并且它并不需要变更着色器。

Single-pass Instanced

单程渲染

Instanced rendering performs a single render pass where each draw call is replaced with an instanced draw call. This heavily decreases CPU utilization. Additionally this decreases GPU utilization due to the cache coherency between the two draw calls. In turn your app’s power consumption will be much lower.

To enable this feature, open PlayerSettings (menu: Edit > Project Settings > Player). In PlayerSettings, navigate to Other Settings, check the Virtual Reality Supported checkbox, then select Single Pass Instanced (Fastest) from the Stereo Rendering Method dropdown.

实例化渲染时，每执行一次渲染，每一个绘制调用会被替换成一个实例化渲染调用。这极大的减少了CPU的使用量，另外，如果两次绘制调用的内存关联性较大，这也会少量地减少GPU使用量。这样，你的程序的电量消耗也会变得更加的低，如果想使这个特性生效，打开PlayerSettings（菜单：Edit > Project Settings > Player）。在 PlayerSettings界面，找到Other Settings，勾选Virtual Reality Supported复选框，然后在Stereo Rendering Method 下拉框里选择Single Pass Instanced (Fastest)。

Unity defaults to the slower Multi pass (Slow) setting as you may have custom shaders that do not have the required code in your scripts to support this feature.

Unity的默认设置是较慢的Multi pass (Slow) ，是因为你能有一些自定义的shader不支持这项特性(single pass)。

Shader script requirements

着色器代码要求

Any non built-in shaders will need to be updated to work with instancing. Please read this documentation to see how this is done: GPU Instancing. Furthermore, you’ll need to make two additional changes in the last shader stage used before the fragment shader (Vertex/Hull/Domain/Geometry). First, you will have to add UNITY_VERTEX_OUTPUT_STEREO to the output struct. Second, you will need to add UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO() in the main function for that stage after UNITY_SETUP_INSTANCE_ID() has been called.

任何非内建的着色器都需要被更新来进行实例化工作。请阅读这个文档来了解如何去做：GPU实例化。此外，你将需要在片段着色器(Vertex/Hull/Domain/Geometry)之前，添加两个额外的变化在着色器的最后部分。首先，你将必须把UNITY_VERTEX_OUTPUT_STEREO 加到output结构体中。其次，你将需要添加UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO（）到main函数里，这样，那个部分就会在UNITY_SETUP_INSTANCE_ID（）之后调用

Post-Processing Shaders

后处理着色器

You will need to add the UNITY_DECLARE_SCREENSPACE_TEXTURE(tex) macro around the input texture declarations, so that 2D texture arrays will be properly declared. Next, you must add a call to UNITY_SETUP_INSTANCE_ID() at the beginning of the fragment shader. Finally, you will need to use the UNITY_SAMPLE_SCREENSPACE_TEXTURE() macro when sampling those textures. See HLSLSupport.cginc for more information on other similar macros depth textures and screen space shadow maps.

你将需要添加UNITY_DECLARE_SCREENSPACE_TEXTURE(tex)宏到输入纹理声明的地方，这样2D纹理数组才能正确地被声明。然后，你必须在段着色器的开始添加一次UNITY_SETUP_INSTANCE_ID（）的调用。最后，你将需要在取样那些纹理时使用theUNITY_SAMPLE_SCREENSPACE_TEXTURE（）宏。你可以在 HLSLSupport.cginc里看到更多关于其他类似的宏深度纹理和屏幕空间阴影映射的相关信息。

Here’s a simple example that applies all of the previously mentioned changes to the template image effect:

这里是一个简单的案例，它应用了之前提过的改变，实现了一个样板图片特效。

struct appdata {    float4 vertex : POSITION;    float2 uv : TEXCOORD0;    UNITY_INSTANCE_ID }; struct v2f {    float2 uv : TEXCOORD0;    float4 vertex : SV_POSITION;    UNITY_INSTANCE_ID    UNITY_VERTEX_OUTPUT_STEREO }; v2f vert (appdata v) {    v2f o;    UNITY_SETUP_INSTANCE_ID(v);    UNITY_TRANSFER_INSTANCE_ID(v, o);    UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);    o.vertex = UnityObjectToClipPos(v.vertex);    o.uv = v.uv;    return o; } __UNITY_DECLARE_SCREENSPACE_TEXTURE(_MainTex);__ fixed4 frag (v2f i) : SV_Target {    UNITY_SETUP_INSTANCE_ID(i);    fixed4 col = __UNITY_SAMPLE_SCREENSPACE_TEXTURE(_MainTex, i.uv);    // just invert the colors    col = 1 - col;    return col; }

DrawProceduralIndirect

间接程序绘制

Graphics.DrawProceduralIndirect() and CommandBuffer.DrawProceduralIndirect() get all of their arguments from a compute buffer, so we can’t easily increase the instance count. Therefore you will have to manually double the instance count contained in your compute buffers.

Graphics.DrawProceduralIndirect()和CommandBuffer.DrawProceduralIndirect() 可以从一块计算缓存里获取所有的参数，所以我们不能简单的增加实例个数。因此你必须手动地加倍实例数量包括你的计算内存数量。

Vertex and fragment shader examplesSee the  page for more information on shader code.

可以通过“顶点着色器和片段着色器例子”页面获取更多关于着色器代码的知识。